Secrets of the Andes

---

“LOOK! The bridge is out! Stop the car—quick!” Bob Holton’s voice was unsteady as he gazed ahead at the place of danger.

Acting on the instant, Joe Lewis pushed the brake pedal to the floor and waited breathlessly, his mind filled with thoughts of tragedy.

The wheels of the small automobile locked, but the momentum carried the car on at a sickening pace. Despite the fact that the tires were new, they slipped over the road easily.

An instant later the youths saw that the distance between themselves and the washout was not great enough. In but a few seconds they would be plunging down the embankment into the swollen river.

There was not a moment to lose. Opening the doors as rapidly as possible, the chums jumped from the car and rolled over on the ground, their faces wet with perspiration.

And they were none too soon. The car sped on, reached the edge of the river bank, and then plunged out of sight.

There was a loud splash as it struck the water, and then all was quiet. The sun continued on its downward path, the faint wind played through the trees. Nothing but two lone boys were left to tell of the misfortune.

“Well,” sighed Joe, at last breaking the silence, “we sure had a tough break, didn’t we?”

“Lucky to get off with our lives, though,” Bob reminded him. “That was about the closest shave I’ve ever had. Wonder why the highway commission didn’t put out a sign?”

“Probably didn’t know the bridge was out. Not many cars go over this road, and it would not be exceptional for this to go unnoticed for quite a while.”

“We’ll sure make a report of it,” said Bob, getting to his feet and brushing off his mud-stained trousers.

Joe laughed unwillingly.

“That’ll be like locking the barn after the horse has been stolen,” he grunted. “Come on,” he went on, “let’s go over to the river bank and see if we can catch a glimpse of the coupé.”

The youths walked over and stared into the swiftly moving water. It had rained in torrents two days before, and the river was now almost a rapids.

“Car’s nowhere in sight,” said Joe Lewis gloomily. “But”—his face lighting suddenly—“it’s insured. So I guess there’s no use worrying.”

“Maybe not about the automobile. But how are we going to get back to Washington?”

“We’ll have to hike to the main highway, I guess,” Joe answered. “It’s about five miles away, too.”

The youths were returning to their homes in Washington, D. C., after having spent a delightful week-end in Virginia. Their accident came upon them in a rather out-of-the-way spot, a great number of miles from the city of their destination.

“If it hadn’t been for that hill,” remarked Joe, as he and his friend walked back up the road, “we would have seen this place in time to stop the car.”

“The hill is here, though,” returned Bob with a grim smile. “So that’s that.”

The boys paused a moment at the spot where they had jumped from the doomed automobile. With one last look at the washout, they turned and began climbing the grade.

“Five miles is a good distance to walk,” grunted Joe, “especially when we want to get home before long.”

“That last you said made the first all right,” laughed Bob Holton, “because on the Sahara and in Brazil we often hiked, not five miles, but several times that far without stopping.”

The friends were refreshed after the idle weekend trip and worked their legs like pistons. Despite their serious predicament, they observed the wonders of autumn with the eye of a nature lover.

Leaves of yellow and brown were lying about the ground in profusion, while others on the trees were almost ready to fall. There was a cool afternoon breeze that gave evidence of winter being not far off.

“Think there’s a chance of getting a ride with somebody?” asked Joe, as the youths followed the curving road.

Bob shook his head.

“Fellows in this part of the country are pretty careful about picking up strangers,” he returned. “Too many stick-ups and robberies. Still we might see some soft-hearted person who would not be afraid to take a chance with us.”

“The question is, though,” began Joe, “will we get in with somebody before night? It’s three o’clock now, and we may have to do a great deal of thumbing before anybody will stop and let us in.”

The road wound through a rather isolated section, with only an occasional farmhouse looming up from behind the trees. It was indeed a poor place to be stranded.

The sun was well down to the horizon when the youths finally reached the through highway. Although they had done their best, they had found it difficult to avoid the many large mud puddles that often reached nearly across the road.

“Now to get down to business,” said Bob, gazing far down the highway. “We’ll surely find a car before long that will pick us up.”

“Here comes one now,” observed Joe. “It’ll be here before long. Come on, let’s get out farther.”

The boys waited for the automobile to come nearer. Then they signaled the driver. But the latter appeared to pay no attention to the young men. A moment later the car whizzed on up the road.

Bob and Joe looked at each other. Their faces clearly showed that they expected the worst.

“Could hardly blame him, though,” remarked Bob. “So many innocent-faced crooks walk the highways that it’s unsafe to pick up anyone.”

“But you know the old proverb,” grinned the other youth. “‘If at first you don’t succeed, try, try again.’ According to that, we—— Look! Here comes another car. Maybe we’ll have better luck this time.”

Again the chums signaled, and were delighted to see that the car was coming to a stop. At a motion from the driver, who was the only occupant, they climbed inside.

“How far ye goin’?” the stranger asked. He was a short, fat man who looked capable of great mirth.

“To Washington,” replied Bob. “We had an accident with our car not far from here.”

“Accident, hey? Not hurt, I hope?”

“No. We were able to jump out in time. You see, we came unexpectedly on a spot where the bridge was washed away. Caused by the recent rain, no doubt.”

“Oh. Tough luck, wasn’t it? And the machine—was it insured?”

“Luckily it was,” replied Joe with a chuckle. “Though we may have trouble in proving it.”

“Fight it to the finish!” said the man, shifting his cud of tobacco to the other side of his mouth. “If you have to, take it to court.”

“I hardly think that will be necessary,” Joe said with a smile. “The insurance company bears a good name.”

“Wonder if this guy’s Scotch?” mused Bob to himself. Only recently the youth had read a good joke about a man of that nationality.

For the next half-hour the three carried on a varied conversation. It was at last broken as they neared a small town.

They had almost entered the city limits when a slowly moving freight train halted them. Reluctantly they settled back and waited.

“This will mean a big loss of time,” remarked Joe, as he gazed far down the track at the seemingly endless string of cars. “I’m anxious to——”

“Listen!” commanded Bob, leaning forward wonderingly. “Did you hear anything? There it is again.”

“It’s a muffled cry for help, coming from one of those freight cars.” Joe had opened the door of the sedan.

With a parting word for the driver, the youths left the automobile and ran down the track, straining their ears for a repetition of the cry.

“There it is again!” declared Joe. “Sounds like a young boy. In that third freight car up there.”

Summoning all their strength, the youths ran on until they were opposite the box car. It was easy to keep abreast with the train, moving as slowly as it was.

The door was pushed back about three feet, leaving barely enough room for the youths to clamber up into the car. Their efforts were not in vain, however, and soon they found themselves inside.

“Where are you?” called Joe, glancing about at the scores of boxes and barrels.

“Here!” a faint reply came from a far corner.

At once the youths turned in that direction, searching for a passageway between the many objects that filled the car. At last they were within a few feet of the corner. But it was not possible to penetrate farther, for a large pile of heavy crates barred the way.

“Let’s get these to one side,” said Bob, and for the next few minutes the young men worked furiously.

Finally they made an opening sufficient for them to pass through.

“Now we’ll see who’s here,” muttered Joe Lewis.

The youths worked their way through the passage, their eyes trying to pierce the darkness.

Suddenly they drew back with a cry of surprise.

---

EMERGING from behind a pile of boxes was a small boy, his face black with dirt that looked the product of weeks. The clothes he wore were soiled and torn, and his shoes barely clung to his feet.

“Thanks!” was all he said, as he glanced up shyly at Bob and Joe.

For several seconds the young men stared wonderingly at this forlorn being, as if trying to account for his presence. Finally Bob broke the silence.

“What’s it all about?” he asked. “What are you doing here?”

The boy hesitated a moment, looked up at Bob and Joe, and then, satisfied that he could confide in them, spoke.

“I—I was caught behind that stuff,” he stammered. “I hid under a pile of bags when they loaded the car so they wouldn’t find me.”

“But why were you in the car?” demanded Joe. “Where are you going?”

The boy waited a moment before replying.

“I don’t know,” he confessed, dropping his head.

There was something about this youngster’s frankness that moved the youths to pity.

“Come,” urged Bob, laying his hand on the boy’s shoulder, “tell us about it. Why did you run away from home?”

“I didn’t want to go to school, that’s why. Ain’t that reason enough?”

“H’m. Don’t like school, huh? Where do you live?”

“Chicago.”

There were exclamations of surprise from Bob and Joe.

While they gaze at the young lad in wonder, it might be well, for the benefit of those who have not read the first two books of The Exploration Series, to tell something about the two youths, and what had been their adventures up to the present time.

Bob Holton, who was generally the leader of the two, was a large, powerful boy of nineteen. His complexion was originally light, but an adventurous life in hot lands had made him bronzed. Wherever he went, he was a prime favorite of all.

Joe Lewis was Bob’s closest friend, the two being almost inseparable. Joe was of medium build and possessed many desirable characteristics. But in a crisis he was never as cool as the other youth.

Fortune favored the boys. Their fathers, Howard Holton and Benjamin Lewis, were noted naturalists, who often wandered to far corners of the globe in search of wild animals for a large Washington museum. The two families thus lived in Washington, their homes being but a few rods apart.

Shortly after Bob and Joe had graduated from high school, they were given an opportunity of accompanying their fathers to little-known Brazil. Here with wild animals and treacherous savages they had many thrilling adventures, which are related in the first volume of this series, Lost in the Wilds of Brazil. The boys proved themselves worthy of being called explorers, and the following spring were given another chance to penetrate the unknown.

On the Sahara Desert they encountered more perils and hardships. How, among other things, they endured a terrible sand storm, went for days without water, and finally fought hostile Arabs for freedom, is related in the volume entitled Captured by the Arabs.

At the time this story opens, the youths would have been in college had it not been for another proposed scientific trip. The naturalists had finally decided to explore the Andes Mountains in South America, and Bob and Joe were given the permission to accompany the men. The boys had argued stiffly that such an adventure would benefit them as much as a half-year at college, to which their fathers had finally agreed. Now less than two weeks remained before the expedition would depart.

As we return to Bob and Joe, who stood staring in amazement at the small lad who said his home was in Chicago, we see that Bob is speaking.

“And you came all this distance?” he asked. “How old are you?”

“Twelve.”

“Aren’t you sorry you ran away from home?” queried Joe.

“I ain’t sorry, but I’m goin’ back. That’s where I’m headin’ now.”

“Why did you change your mind?” Bob asked.

“Even school’s better’n goin’ without anything to eat,” the boy said.

For some time Bob and Joe sat staring at the floor. Everything was clear to them now. They were impressed by this little fellow’s resourcefulness in finding his way freely about.

Suddenly Joe glanced up. He had almost forgotten that he was on a moving freight train. The cold sweat burst out on his forehead as he saw that they were now traveling rapidly.

“No chance of getting off now, Bob. I guess we’re in for it. Where does this train go?” he asked the boy.

“Chicago,” was the response. “That’s where this car is headed for. I made sure before I got in it.”

Bob grunted.

“We’re booked for a ride, I guess,” he said. “Still there may be a chance of getting off at some town not far from here.”

“That’s what we’ll hope for,” the other youth said, nodding. He turned to the lad. “Can you find your way home after you reach Chicago?”

“Sure. This ain’t the first time I’ve run away. Gettin’ back ain’t what worries me.”

“What does?” inquired Joe.

“My old man. He’ll be mad enough to bite nails. Bet he’s got the razor strop hangin’ up now waitin’ for me.”

Bob and Joe smiled. The personality of this waif touched them.

“Bob Holton is my name, and this is my friend, Joe Lewis.”

A small hand was extended.

“I’m Spike Weaver, the son of a horse thief.”

The youths burst out in laughter.

“A horse thief?”

“Yes,” the boy said. “That’s what the old man used to be. I’m not onto him now, I been away from home so much.”

Another outburst of laughter followed. The youths were beginning to take a liking to this small wanderer.

One thing stood out in the young men’s minds: the family to which this boy belonged was evidently of a very low type morally. Little wonder that young Spike had turned out to be a worthless ne’er-do-well. There was apparently little hope for his future.

“Why don’t you go to school and try to make something out of yourself?” asked Bob. “Wouldn’t you like to be a big business man, or doctor, or merchant, or naturalist?”

“What’s that?” the lad asked.

“A naturalist is a scientist who travels to little-known places to collect wild animals for a museum or college,” explained Bob.

There was a glint of interest in young Spike’s eyes. He had absorbed this definition eagerly.

“Does he shoot with a big rifle, and camp out?” Spike demanded.

“That’s exactly what he does,” Bob replied. “And he usually has plenty of adventures, too.”

“Boy! That sounds swell! Wonder what it feels like to fire one of them guns.”

“Feels all right after you get used to it,” Joe said.

“How do you know?” Spike asked, as though he felt that Joe was talking of something that he knew nothing about.

“My friend has fired them,” explained Bob. “And so have I.”

At once the lad was all excitement.

“You’ve really hunted wild animals? Tell me about it.”

During the next hour Bob and Joe related some of their experiences in Brazil and North Africa, while their newly made young friend listened breathlessly. By the expressions on his face they knew that he was absorbing every word with interest. When they had finished, his admiration for them was beyond expression.

“Gee! You two are real naturalists,” he said.

“Not yet,” corrected Bob, “though we hope to be some day. To be a naturalist you must go through college and get your lessons every day. But it isn’t hard if you want to like it.”

For a time young Spike seemed lost in thought. Finally he roused himself and turned to his friends.

“I’m goin’ home and go to school, so I can be a naturalist,” he said conclusively. “And then maybe I can have a lot of fun huntin’ and campin’, like you fellows do. I always did want to do that.”

Bob and Joe glanced at each other. Did this lad’s decision mean anything, or was it merely a childish notion? At least they had induced him to attend school temporarily.

Joe started to speak, but Spike silenced him.

“Look!” he cried. “We’re comin’ to a stop. This must be a town.”

The boy was right. The train was gradually slowing up at a spot where the track had branched into several switches. At last it came to a full stop.

“Now’s our chance to get off,” declared Joe. “We——”

“Keep still,” hissed Bob. “Somebody’s coming down the track. It may be a railroad policeman, or ‘bull,’ as the hoboes call them.”

“Let’s hide behind these boxes,” suggested Joe. “He may be coming in here.”

Quickly, yet quietly, the three concealed themselves in a corner of the box car. Then they waited.

The sound of someone walking grew louder, and the next moment a man stopped at the side of the box car. There was the sound of a door rolling forward, and then the click of a chain. Less than a minute later he was on his way up the tracks.

Hastily the hideaways slipped out from behind the boxes and into the center of the car.

Bob uttered an exclamation of dismay.

“That fellow locked the door!” he cried. “We’re trapped!”

---

SPIKE uttered a cry of fright, while Joe dashed forward to make sure that his friend was right.

As Bob had said, the railroad man had fastened the door securely. There was an opening of about eight inches, across which was a heavy chain that terminated at a large lock. In order to cut the chain, a file would be necessary.

Of the three prisoners, Spike was the first to resume his natural attitude. Perhaps this was due to his wide experience in riding freight trains. At any rate he seemed to forget his plight and resign himself over to any fate.

“Tough luck!” the lad said. “Guess you guys will have to ride with me to Chicago. May be several days before we can get anything to eat, too.”

“That’s the worst part about it,” lamented Bob. “It may be days, or even weeks, before we’ll reach our destination.”

Bob and Joe were inclined to be downhearted, but their young friend was cheerful.

“Don’t you worry,” he consoled them. “I’ve been in tight fixes like this many a time, and I’ve always got out all right. One time I went out West and got locked in just like we are now.”

Young Spike sounded like an experienced vagabond, and the youths could not help laughing.

“How did you get out?” asked Joe, after the laugh had subsided.

“It was easy. When we stopped at a town I just waited for some hobo to come along. Somehow he got ahold of a file and had me out in a jiffy. Hoboes are good to do anything like that for you.”

“Let’s hope history will repeat itself,” muttered Bob, who, along with Joe, did not like the prospects of a trip to Chicago.

Less than ten minutes later there was a slight jar, and the train started moving. Although pulled by a large engine, there was little chance of high speed, for a line of cars over a half-mile long stretched far down the track.

Bob, Joe, and Spike crowded before the crack to catch a glimpse of the town at which they had stopped. But aside from a number of freight cars and old buildings, there was little to be seen.

“Suppose we arrange boxes in front of what little opening there is,” suggested Joe. “We may as well amuse ourselves by looking out.”

“That reminds me,” burst out Spike. “I want to see if anything in this car has stuff to eat in it.”

He at once began a search of the many boxes, bales, and crates that were packed in each end of the car. Suddenly he gave a cry of delight.

“Here’s apples!” he cried excitedly. “Gee whiz! Who says we don’t eat?”

But the fruit was in tightly nailed crates, which could not be easily opened.

“Come here, fellows!” shouted Spike. “Give me a hand! You don’t expect me to open ’em when there’s big guys like you around, do you?”

“Wait a minute!” commanded Bob. “Whose apples are they?”

“Whose are they? I don’t know. Why?”

“Do you think it’s right to get in a box car and eat up somebody’s apples?”

“Ah, gee whiz! You ain’t gonna back out of a chance like this, are you? Come on. Be a sport.”

Bob stoutly refused.

“We’re not going to open any boxes or crates around here, and you’re not either! Get that and get it straight! Of course if we have to, to keep from starving, we will. But not now.”

Against this stout protest there was no use persisting, and Spike finally walked sullenly back to his seat before the slightly open door.

“You guys sure are the berries,” he said with an ironic smile. “You’ll never get anywhere that way.”

“That’s where you’re wrong,” Joe corrected him. “We will and you won’t, unless you get such notions out of your head.”

“Ah, blooey!”

A half-hour of silence followed, during which time the three gazed absently out, watching the farms, the forests, the rivers and creeks slip by. They were beginning to enter the Appalachian Mountains, and more of natural beauty promised to be visible.

But Bob and Joe did not care to observe the beauties of nature just then. Their thoughts were dwelling on the probabilities of the future. What lay in store for them? Would they be able to get home in time to accompany their fathers to the Andes Mountains, or would fate rule that they remain for an indefinite period in this box car? If the truth were known, the youths were not a little worried.

Darkness was beginning to enshroud the travelers, and the necessity of making improvised beds moved them to action. There was a large pile of burlap sacks in a far corner of the car. These they arranged a short distance from the partly open door.

“I don’t think these bags are inhabited,” smiled Joe. “They look almost brand-new. At any rate we’ll take a chance with them.”

“We’ll have to,” agreed Bob, who realized the necessity of a rest after such an arduous day.

However, the travelers spent an hour or so longer gazing out at the dim outlines of the mountains. Although Bob and Joe were tired, they had an uneasy feeling about resigning themselves over to sleep. Something unexpected might happen during the night.

Finally Bob arose and walked over to his bunk.

“Suppose we turn in,” he suggested. “We may need plenty of energy tomorrow. It’s possible for almost anything to happen, you know.”

Joe nodded and took his place beside his friend, but Spike announced that he would remain up awhile longer.

Almost at once the youths fell asleep. But from their experiences in dangerous lands they had learned to keep one eye open as a precaution.

This proved to be unnecessary, however, and they awoke the next morning greatly refreshed.

“We’re on the other side of the mountains,” observed Joe, as he stretched and glanced out of the crack.

“Now maybe we can make better time,” Bob said, moving over to the door.

The three travelers were forced to begin the day without breakfast. Spike insisted that they open the crates of apples, but Bob firmly refused.

“We may find some way out today,” the youth consoled him. “If we have to, we can eat a few of those apples tonight.”

All morning the train continued on its journey, passing small towns and villages. Along toward noon it stopped at Charleston, West Virginia, where after an hour of switching it was left on a side track.

Suddenly Joe, who was standing by the crack, caught sight of a trainman not far away. The man’s face was rather pleasant, with no trace of gruffness.

“There’s a chance,” Joe said. “Let’s ask him to help us out.”

“No, don’t,” pleaded Spike, pulling Joe back.

“Why not?”

“’Cause if he gets you out he won’t let me keep in this car to Chicago.”

“But what about Bob and me? We don’t want to ride all that distance.”

“No. Go ahead and call him,” directed Bob, who was moving up to the door. “Spike can find another car that’s going to Chicago. We want to get home.”

Disregarding the lad’s protest, Joe shouted and motioned for the man to come to the box car. There was a look of surprise on the fellow’s face as he moved over to where the three were trapped.

“What’s it all about?” he demanded. “You guys trying to steal a ride, huh? Come on out of there and pick a car that ain’t got anything in it.”

“We can’t get out,” explained Joe. “Locked in, I guess. That’s what we wanted of you. See if you can get the door open.”

“Oh! So they penned you up, huh? Yeah. I see that locked chain now. Sorry, but I’m afraid I can’t do anything for you.”

“But—but we’ve got to get out,” Joe said persistently. “We haven’t had anything to eat for quite a while.”

The man hesitated a moment.

“Got any money?” he asked.

“Yes.”

“Let’s see it.”

Joe held up a half-dollar.

“O.K. There’s a grocery a block from here. Want me to get you something?”

Delighted at such a chance, Joe instructed the trainman to purchase several articles of food that would be sufficient to last for several days. It was with a feeling of high hope that the youths watched the man walk in the direction of the store.

In less than fifteen minutes he was back and handed Joe a sack of groceries in return for money. In recognition for his service, the youth tipped him generously.

“Now for a delicious meal,” said Bob, smacking his lips. “And will we eat!”

The boys did eat, and felt much better for it. When they had scraped up the last crumb, they stretched out on the burlap sacks.

The remainder of the day passed without incident. Darkness was just setting in when, with a slight jerk, the train started moving.

Even though they had expected an undisturbed sleep, Bob and Joe were delighted that they were again on their way. Every mile left behind would mean that they were nearer Chicago, which was perhaps the only city at which they could hope to escape from their prison.

“Let’s hope we make good time now,” breathed Bob, as he and his friends turned in, to get what sleep a rumbling train would allow them.

All through the night the freight rattled on, this time much faster than before. Although several stops were made, the train made unusually good time, pulling into Cincinnati late the next morning.

“Here’s where we’ll have to wait,” said Joe. “They might keep us switched here for several days.”

Almost at once their box car was sidetracked, and was not moved until late the next day. About four o’clock another engine was attached, a much shorter train being formed. Then slowly it pulled off the switch and found a through track.

Bob and Joe could hardly believe their eyes. Were they to leave Cincinnati so soon?

An hour later this question was answered. The boys found themselves speeding along to Chicago, after having remained on the switch less than twenty-four hours.

“I suppose we’ll stop at every town and small city in Indiana,” said Bob gloomily. “Even though this is a fast freight, a delay will be almost inevitable.”

The youth was right. It was nearly three days later when the train entered the city limits of Chicago. Gary and other cities of the Calumet district had been left behind.

After what seemed like hours of constant travel in the metropolis, the freight stopped at a busy switch yard, where scores of trains were moving in all directions.

Suddenly Bob cried out in delight as he caught sight of a man walking up the track. The youth recognized this fellow as the one who had snapped the lock on the box-car door, making the young men and Spike prisoners on the train.

Bob at once called the man, who, upon hearing, turned about in surprise.

“Why—what—what are you doing in that car?” he demanded angrily, as he caught sight of the youth.

“We want to get out!” Bob’s voice was cool and determined.

“But how did you get in there? I thought I locked that door. I——”

“Let us out and we’ll tell you all about it,” Bob pleaded.

The man pulled a bunch of keys out of his pocket and immediately unlocked the door. Bob hurriedly rolled it open and jumped out, followed by Joe and young Spike.

It was good to feel their feet on the ground again. Bob and Joe could have cried out in joy. But there was little time to do this, for the trainman demanded an explanation of their presence.

Briefly Bob narrated the circumstances that led to their boarding the train, shielding Spike as much as possible. When he had finished, the man viewed the young lad critically.

“I think I’ll turn you over to the yard master,” he said to Spike, “and see that you get what’s coming to you.”

He roughly caught hold of the boy’s arm and pulled him forward.

“Wait a minute,” begged Joe. “Spike didn’t do any harm. He’s promised to quit running around and go home and go to school.”

“Well, he ain’t gonna get no sympathy from me. I got no use for a kid that rides freights.”

He gave the boy another pull, this time so violent that the latter slipped and fell, bruising his face on the cinders.

Bob grew furiously angry. He stepped boldly up to the trainman.

“Let the boy alone!” he demanded, his eyes seeming to penetrate the man.

---

BEFORE the blaze in Bob’s eyes the man shrank back, hesitated a moment, and then turned in the direction of the freight station.

“All right,” he snarled. “But don’t let me catch the kid around here again, or you either.”

He walked up the track to the end of the train, then disappeared behind the engine.

“Gee, that was swell of you,” said Spike to Bob. “You sure had that guy scared.”

“He was glad enough to get out of it,” laughed Joe. “Old Bob wouldn’t have left a grease spot of him.”

“But now,” began Bob, anxious to turn this tribute aside, “let’s figure out what to do. I suppose the only thing——”

“I want to get home,” Spike interrupted. “I may have something comin’ to me, but the sooner I get it over, the better.”

“Where do you live?” Joe asked.

“Only about a half-mile from here.”

Joe got a piece of paper and pencil out of his pocket. He tore off one corner and wrote down the address of himself and his friend. This he gave to Spike.

“Here,” he said. “Write us a letter some time. Now where do you live?”

Spike told him, and then, with a warm good-bye, he left the youths and hurried down the track.

Bob and Joe watched the lad until he disappeared from view. Even after they lost sight of him, they stood gazing in that direction until a locomotive whistle roused them.

“He’s a good kid, all right,” smiled Bob. “Might be an aimless wanderer, but he has a lot in him.”

“Got a keen sense of humor, too,” said Joe, and then added: “I wonder if he’ll really go to school and make something out of himself, as he said he would?”

“Hard telling. A lot can happen to change his mind, you know.”

For several minutes Bob and Joe watched the busy scene about the tracks. Finally a factory whistle from afar prompted Joe to glance at his watch.

“Nearly two o’clock,” he announced. “Come on. Let’s hurry down to the freight station and see if we can send a telegram to our folks. If we hadn’t lost the car in that river, we would have been home several days ago.”

The youths moved down to the building and went inside. After making several inquiries they finally found the main office, where they were permitted to send a telegram. Then they left the building and walked in the direction of the street.

“Good old Chicago,” smiled Joe. “It’s only been a couple of months since we were here.”

Bob stopped suddenly.

“That reminds me,” he started. “We came here with our dads to see a Mr. Wallace, who’s with the Museum of Natural History, didn’t we? And this Mr. Wallace is planning on going with our dads’ expedition to the Andes Mountains, isn’t he? Do you suppose he’s left for Washington yet?”

Joe’s face lightened.

“I see what you mean,” he said. “We can go and see him, and incidentally we can borrow enough money to get home on. Suppose we go to the museum now.”

The boys were familiar with Chicago and had no difficulty in taking a street car. After a half-hour’s ride they got off within a few squares of the museum. A ten-minute walk brought them to the main entrance.

At the office they made inquiries about Mr. Wallace and finally found him in a laboratory on the second floor. He smiled broadly as he recognized Bob and Joe.

“Well, this is an unexpected pleasure,” he said, extending his hand. “What, may I ask, are you fellows doing in Chicago? Why aren’t you getting ready for that Andes expedition?”

“It isn’t our fault that we’re here,” laughed Bob, and then proceeded to tell of the events that led to their presence. “Since we finally landed here, we thought we’d come to the museum and see if you had left for Washington yet,” he concluded.

“A strange chain of circumstances,” the scientist breathed. “Not many could go through all that in the course of a few days. No doubt it was your first experience as hoboes, was it not?”

“First and last,” returned Joe. “We’ve had all we want of it. But now,” he went on, “when are you going to Washington? The expedition leaves in little more than a week.”

“I had planned to go day after tomorrow,” Mr. Wallace said. “I think everything will be in readiness by that time. I’d like to spend at least three days in Washington talking with your fathers and others of the expedition before sailing. Of course you fellows are familiar with the details of the expedition, are you not?”

“Quite the contrary,” returned Bob. “You see, when the matter was first mentioned, about a month ago, there was not much known about it. Our dads declined to say much, because they were not absolutely sure they were going. Joe and I, though, had a sort of feeling that they were going, and finally got permission to stay out of college at least a half-year.”

“So you could go with the expedition?” interrupted the scientist.

Bob nodded.

“We figured we’d get as much good out of such a trip as we could get in a university,” he explained. “Then, too, there’s a chance of making money by taking motion pictures, as we did on our other expeditions.”

“I think you did wisely,” Mr. Wallace said. “It usually isn’t good for a fellow to get out of college too young. When an extraordinary chance like this turns up, it’s best to take it.”

He motioned for the boys to follow him into his office, where several chairs were arranged about the desk. A large bookcase occupied a whole end of the room, while opposite it was a case of instruments and preservatives.

“Sit down,” he directed them, “and we’ll talk over this Peruvian expedition.”

Bob and Joe did as directed, glad of the chance to rest their tired limbs.

Mr. Wallace procured an atlas, opened it to a map of Peru, and drew an imaginary line in the lower right-hand corner.

“Here’s Cuzco,” he pointed out. “We’ll probably make it or some other near-by city our base. From there we’ll go into the Andes Mountains on our varied scientific quests.”

“But what—what is the main purpose of the expedition?” inquired Joe. “Of course, you and Mr. Holton and Dad are naturalists, who want to get specimens of animal life. But that isn’t the chief aim of the expedition, is it?”

“No. It is being sent out by the division of ethnology at the museum in Washington. The scientists in that field have in mind mainly to study the ruins of the vanished Inca civilization. Those Indians, you know, that built so many marvelous works of architecture. That’s about as much as I know about them, though,” he laughed. “My line runs straight through the field of natural history and zoölogy, and incidentally anatomy, histology, taxonomy, embryology, ecology——”

“That’s enough!” interrupted Bob, smiling sheepishly. “You don’t expect Joe and me to be acquainted with all those subjects, do you? We’re pretty good shots, but as scientists we’re as yet a complete flop.”

A general laugh ensued, after which the naturalist again pointed to the map.

“We are to explore the region northwest of Lake Titicaca,” he continued. “I understand there are some very high peaks in this range, all the way from ten to twenty thousand feet in altitude.”

“These Incas,” started Joe, “when did they live? It hasn’t been so very long ago, has it?”

“Not as time is usually thought of. The sixteenth century witnessed their downfall. This was at the time of the Spanish South American explorations, you know.”

“Those Spaniards sure saw something unusual and unexpected,” remarked Bob. “This mountainous region was chock-full of architectural wonders, all built by the Incas.”

“Something tells me we’ll see sights, all right,” said Joe. “It will be good to get away from home again—into the unknown, I mean. And that reminds me. Would it be possible for you to lend us enough money to get back to Washington?”

“Why—of course. How much do you need?”

“Fifty dollars will pull us through. Perhaps we can get along on less than that,” was the answer from Bob.

“All right. I’ll see that you get it. But wait! I expect to go day after tomorrow with a friend, who is driving East on business. There will be plenty of room for two more. You fellows don’t have to get home at once, do you?”

“No, we don’t have to,” returned Joe. “We——”

“Suppose you be my guests until then. I’ll be only too glad to have you. In the meantime we can be discussing the coming expedition.”

“We’d sort of hate to do that,” Bob said. “It will mean a lot of trouble to you.”

“Forget it! I’ll be only too glad to have you.”

“Well, all right, if you——” Joe began.

“We’ll call it settled,” Mr. Wallace said. “And now, since my day is practically over, we may as well go to the house. That is, if you’re ready.”

“We’re ready any time,” Bob told him.

The three went outside, to a place where the naturalist’s automobile was parked. All got inside and drove through the city till they came to a beautiful suburb.

“Here’s my place,” said Mr. Wallace, pointing to a large house of rather costly design.

Inside, the youths were introduced to Mrs. Wallace, who made them feel perfectly at home.

“I hate to see Mr. Wallace leave on an expedition,” she said, “but I can appreciate his interest in science. In fact, I have often wished I could accompany him. Be a sort of Mrs. Martin Johnson, you know.”

“I wish our mothers were like that,” laughed Bob. “If they were, perhaps Joe and I wouldn’t have so much difficulty in getting their consent to go with our dads.”

A bountiful dinner was soon served, Bob and Joe eating heartily.

“And now I have a surprise for you,” Mr. Wallace said, when the meal was over. “It is something I know we all will enjoy, especially in view of what is to come.”

The young men looked inquiring.

---

“WHAT is the surprise?” inquired Joe Lewis anxiously.

“This: I made arrangements for a movie to be shown—purely for our own benefit,” the naturalist explained. “It deals with Peru and the Andes.”

“The region we’re going to explore!” cried Joe, delighted beyond words. “Why, that will be wonderful!”

“I’ve never seen it,” Mr. Wallace said. “But the chances are it will be good. Perhaps we had better go before long. It is to be shown at eight o’clock, and we haven’t a great deal of time to get down there.”

“Where?” inquired Bob.

“To the museum—in the auditorium,” was the response.

Mrs. Wallace asked that she be permitted to go also, and the others consented at once. The wonderful civilization of the ancient Inca Indians she knew not a little about.

At the museum they found several score people waiting for the movie to be shown. There was a friendly gathering for a half-hour or so, at which Mr. Wallace introduced a number of scientist friends from the museum and Chicago universities.

Then the lights were switched off and the movie was projected. It proved everything and more that Bob and Joe had expected, showing the fascinating country of Peru.

The shy Indians with their flat “pancake” hats, the curious llamas and alpacas, the magnificent heights of the mighty Andes, the many old ruins of the Incas—all these and more were depicted on the screen.

It was very inspiring, especially to the boys and Mr. Wallace, who were delighted that before long they would be able actually to visit those wonderful places.

During the drive home the naturalist’s conversation was directed chiefly about this inspiring country, his excitement being almost like that of a small boy. But if the naturalist was impressed, the youths were still more. They longed for the great day to come when they would leave for the wonderland of Peru.

It was so late when they arrived at the Wallace residence that the youths and their hosts decided to retire at once.

“I’m not going to the museum today,” announced the naturalist the next morning at breakfast. “There is so much that has to be done in the way of preparing for the coming expedition that I won’t have time for anything else.”

“If there’s anything Joe and I can do for you, we’ll be glad to do it,” said Bob. “Our preparations won’t begin until we get back to Washington.”

The young men proved to be of valuable service to the scientist. Their previous experience in preparing for exploration ventures enabled them to offer valuable suggestions to Mr. Wallace, even though the latter had made numerous trips for the good of science.

The vast resources of the great metropolis enabled them to find anything that the naturalist needed in the way of outdoor equipment. All that day and half of the next were spent in the business district.

“Now if you fellows like sport, as I do, what do you say about a little target practice?” Mr. Wallace asked them, after the noon lunch.

“What do we say?” Joe was overjoyed. “Lead us to it!”

In the extreme rear of the lawn was a large rifle range. Here, with the guns that Mr. Wallace generously furnished, they took turns exercising their skill at the trigger. Bob easily placed himself above the others by striking the very heart of the bull’s-eye.

“I thought I was a fair shot,” smiled the scientist. “But you have me beat by a mile.”

“Just happened that I hit it, I guess,” Bob said modestly.

But when he again was able to send a bullet almost directly over the first one, the others knew that it did not just happen.

“Wonderful to be such a shot,” remarked Mr. Wallace. “I suppose it has been the secret of your emerging unharmed from the unknown, hasn’t it?” he said laughing.

“Trying to kid me, are you?” smiled Bob. “Joe and I may be green, but another expedition or two will make us full-fledged explorers. At least we hope so.”

Mr. Wallace grinned.

“That’s what we all think,” he said. “But the fact is, we never do get to be what you call full-fledged explorers. I’ve been on a good many expeditions, but I don’t know much even now. To me it’s interesting that I got my start in scout work. The Boy Scout organization is one of the greatest on the globe.”

“So did we, to a certain extent,” said Bob. “Although the fact that our dads are explorers perhaps accounted for a still earlier interest.”

The youths and the naturalist spent the better part of the afternoon on the rifle range. Then they went to the house, where in Mr. Wallace’s extensive library they read still more about Peru and the Andes.

That evening they spent quietly, for the next day they were to start on the trip to Washington. The naturalist’s friend, with whom they were to drive to the East, was to come after them early the next morning.

And early it was. Too early for the youths and Mr. Wallace, who had barely finished breakfast. But they were packed and ready, and so lost no time in getting their belongings together.

The friend, whose name was Wilson, was a newspaper man, often traveling East in the interest of his profession. He was good-natured and talkative, at once taking a liking to Bob and Joe.

When everything was in readiness, Bob and Joe and the men took their places in Mr. Wilson’s automobile and, with a warm farewell to Mrs. Wallace, started down the driveway.

Soon the youths would be home—and on their way to the mysterious Andes!

---

AS the automobile sped toward the thoroughfare, Bob and Joe settled back for the long ride. Now that they were at last heading for Washington, the boys were becoming impatient, although they had enjoyed the last few days immensely.

Until after they had left Chicago, Mr. Wilson was rather quiet, bending his efforts solely on managing the car. But when the metropolis had disappeared from view, he inquired about his friends’ expedition into the Andes Mountains.

“Perhaps I’m not much of an adventurer, but somehow I wouldn’t care for that sort of a life,” he laughed, after Mr. Wallace had related the outlines of the expedition. “I wouldn’t mind taking a trip to that place—put up at a hotel, or the like. But when it comes to straying off the traveled road, well——” He stopped meaningly.

Bob laughed.

“It’s a good thing people aren’t all alike,” he said. “If they were, either the wilds or the civilized places would be filled to capacity.”

Although the youths were anxious to reach their destination, they found the drive East interesting, even though they had made it before. Their attention was so held by the many interesting sights that, almost before knowing it, they found themselves in Pittsburgh, after having eaten a lunch several hours before. In the business district they engaged rooms in a small but comfortable hotel.

If Mr. Wilson and the naturalist were tired, the youths were not. They insisted on taking a look at Pittsburgh, which they had not seen for many months. An hour or two of looking around and they would return to the hotel, remarked Bob.

During that time the young men found much to hold their interest. The great fiery blast furnaces, the towering skyscrapers, the crowds of pleasure seekers, and the lights of river boats all kept them gay with amusement.

At last, when they finally made themselves return to the hotel, they found that their friends had gone. Evidently the lure of a great city was too much for them.

“And Mr. Wilson said he was dead tired,” said Joe with a smile.

“They’re no different from us,” said Bob. “Want to keep on the go, I guess.”

Mr. Wallace and his friend did not return until late, much to the amusement of the youths. Both men wore a sheepish look as they caught sight of Bob and Joe.

“Sorry, but we just had to get out,” grinned the newspaper man, walking drowsily through the lobby. “Couldn’t stand it to stay inside.”

“Perhaps you’ll pay the penalty of oversleeping,” laughed Joe, “and we won’t get started until late.”

Joe proved wrong, however, for early the next morning they were up making ready to resume the journey. From Pittsburgh the traveling promised to be slower, owing to the increased traffic and mountainous country. But Mr. Wilson was determined to make good time, and did, reaching York, Pennsylvania, at one o’clock.

Here the youths and the naturalist were to take their leave, while the newspaper man would continue to New York City. Had he not been in a great hurry he would have insisted on driving them on to Washington. As it was, his business prevented his doing so.

With a hearty farewell, the boys and Mr. Wallace left his car and made their way to a railroad station, where they boarded a train for the nation’s capital.

An hour and a half of traveling brought them to Baltimore, and now the youths began to feel that they were in home territory. In this city a delay was inevitable, but at last the train resumed its journey to Washington, which it reached in due time.

Since Mr. Wallace and the boys had not known exactly when they would arrive, they had not expected anyone to meet them at the station. But much to their surprise they found that Mr. Holton and Mr. Lewis were waiting for them when they went down from the tracks.

“Boys!” cried Mr. Holton excitedly. “And there’s Wallace, too. How are you, old man?”

There followed a wild shaking of hands, patting of backs, and general welcome, in which Mr. Wallace took as large a part as the others.

“How did you know we would come on that train?” inquired Bob wonderingly. “Mr. Wallace didn’t tell you, did he?”

“Not exactly,” Mr. Lewis returned, picking up a suitcase. “But he said you would probably get near Washington today, and that York, Pennsylvania, would be your junction point. So Howard”—referring to Mr. Holton—“and I called up the station to find out when the train would get in. We were here this morning, when the early one arrived.”

The newcomers were led to Mr. Holton’s car, which was parked a short distance away. Glad of the chance to relax, the youths and Mr. Wallace threw themselves tiredly into the seats.

As mentioned previously, the respective homes of Bob and Joe were located next door to each other, almost at the edge of the city. They were not of costly design, but were comparatively new and pleasing.

Mr. Holton had barely brought the car to the curb when the boys’ mothers, along with Bob’s small brother and Joe’s sister, came out to meet them. There followed another greeting, if anything warmer than the first. Mr. Wallace, upon being introduced, received a hearty welcome. It might be added that he was to remain with either the Holtons or the Lewises until the expedition would depart for South America.

“Now tell us what happened,” urged Mrs. Lewis, Joe’s mother, when everyone had assembled in the living room of the Holton home.

Briefly Bob related the adventures of himself and his friend, from the time they lost the car in the river to the present. He told of coming to the washed-out bridge, of the forced abandoning of Joe’s coupé, and of boarding the freight train where Spike Weaver was trapped. The forced ride to Chicago, the calling on Mr. Wallace, and the eventful days that followed were described fully, while the others listened breathlessly.

“Quite an experience,” commented Mr. Holton, when his son had finished. “Not many could have gone through it all.”

The friendly gathering lasted until late that afternoon. As there was no use making further preparations for the coming expedition, all but Bob and Joe took it easy. The youths, however, thought it best to notify the insurance company about losing Joe’s car.

At request, the company agreed to send out an investigator without delay. He arrived as soon as was promised and asked that Bob and Joe accompany him to the spot where the car plunged into the river.

When they arrived at the familiar spot, Bob and Joe were not surprised to see that workmen were repairing the washed-out bridge. The men were aware that a car was at the river bottom.

“I’ll take a few notes,” said the insurance man. “Then we’ll go back. And let me assure you that this matter will be looked after promptly.”

Back at their homes, Bob and Joe were surprised to see a tall young man of perhaps twenty-five conversing with the three naturalists in the Holton library.

Mr. Lewis looked up suddenly as he caught sight of his son and Bob.

“We’ve a surprise for you,” he said smiling. “Part of the Andes expedition is going by airplane.”

---

THE surprise of Bob and Joe was almost inconceivable. They stood staring for several seconds before either seemed to grasp the full significance of the naturalist’s words.

“Airplane? Going by airplane?” gasped Joe. “How come?”

His father laughed.

“We expected to see you fellows startled,” Mr. Lewis said. “But that you would show such unusual astonishment we did not in the least anticipate.” He turned to the stranger. “This,” he went on, addressing the youth, “is Mr. Karl Sutman, who is going to take several members of the expedition in his airplane, or rather monoplane. Karl, I want you to meet Bob Holton and Joe Lewis, the young men we were just talking about.”

“Glad to know you, fellows,” the aviator greeted, extending a hand.

“Pleased to meet you, Mister——” Bob began, but was interrupted.

“Karl, if you don’t mind,” the tall man laughed. “I don’t care for that ‘mister’ stuff. First name fits me good enough.”

“Good enough for us, too,” said Joe with a smile. “Call us Bob and Joe.”

These informalities tended to bring about a feeling of friendliness which was noticeable in the conversation that followed.

“Will you please explain how it all came about?” asked Bob. “This airplane stuff almost took Joe and me off our feet.”

“Off your feet you’ll be in a few days,” chuckled the aviator. “That is if you ginks are picked out to go with me in the plane.”

“If there’s any air traveling, we want to be in on it,” Bob assured him. “But—” he hesitated a moment—“how did it all come about?”

“I’ll tell you,” Mr. Lewis said. “Karl’s dad and I are very good friends—have been for many years. Now when Karl learned of this coming expedition, he at once looked me up and offered to take part of us in his monoplane. All that he’ll charge will be for the gas and oil, and he’ll pay a share of that. The fact that he is a licensed transport pilot makes the whole thing a pretty safe venture.”

“And I’ve had six hundred hours of flying—without a single mishap,” Karl added proudly. “The monoplane I own is one of the fastest and most efficient machines there are. It’ll do a hundred and fifty miles an hour with no trouble at all.”

“Sounds well enough,” smiled Joe. “Tell us some more.”

During the next few minutes the young aviator explained in detail the plans made for the trip. His machine, he said, could carry four passengers and the pilot, and there was a possibility of adding one more. Just who those passengers were to be, the others could decide. The course they would follow he had mapped out carefully, taking into consideration the possibility of having to land at any time. Norfolk, Virginia, would be the last large American city they would see. From there they would proceed south over the Bahama Islands and Cuba, and then on to the north coast of South America. At Bogotá, Colombia, a stop would probably be made for fuel. They would then continue along the coast mountains (Andes) over Colombia, Ecuador, and into Peru. At Mollendo, a small but important coast town, the air travelers would wait to join the other members of the expedition, who would arrive several days later by steamship.

When Karl had finished, the youths were overflowing with enthusiasm. Their imaginations had been captivated by the prospects of a unique air trip into the Andes. That they could accompany Karl they sincerely hoped.

“Of course,” began Joe, addressing his father, “Bob and I will be among the passengers, will we not?”

Mr. Lewis looked grave. He did not have any too much faith in aviation.

“We’ll see,” he replied. “Your mothers will have to give their consent, you know. It may prove difficult to get that.”

“I think we can bring them around,” Bob said, with an optimism that he was far from feeling, “especially if you and Dad decide to go. And you will, won’t you?”

“Impossible for me to do so,” returned Mr. Lewis. “I’ve already made reservations on a steamship. As for Mr. Holton, he may make arrangements to go.”

“But right now,” started Karl, rising, “how would you fellows”—referring to Bob and Joe—“like to come with me out to the airport? I want to show you the ’plane.”

“Lead us there!” cried Joe at once. “We want to take in everything.”

The youths’ fathers had been to the airport the previous day, and so did not care to go again. The boys and Mr. Wallace, however, desired to see the monoplane, especially since there was a chance of their becoming passengers.

It was nearly noon, but the four decided to leave at once. They could get a lunch somewhere else, perhaps at the airport.

“Besides, we’re not hungry,” explained Joe, when the others asked that they leave an hour later. “Excitement and activity make us forget all about eating.”

At the airport the youths and Mr. Wallace were taken to a corner of the field, just off the cement runway. There, before their eyes, was a large white monoplane, shining brightly with a coat of fresh paint.

“Ain’t it a dandy?” Karl was beaming all over with pride. “Just been completely inspected. It’s just r’arin’ to go!”

They walked up to the machine to examine it at close quarters.

“Sure a peach for looks,” commented Joe. “Got an air-cooled motor, too. How about getting inside?”

“Go ahead. You’ll find it as accommodating as a street car.”

“It’s all of that,” agreed Bob a moment later, when he had opened the door and stepped into the cabin. “Those comfortable deep seats appeal to me.”

“Seats aren’t as important in an airplane as in a bus,” laughed Karl. “No bumps in the air.”

On either side of the cabin were two chairs, placed several feet apart. In the middle of the floor was a small folding table, which the boys guessed had been placed there by Karl as a convenience to members of the expedition. A wide glass window separated the pilot’s cockpit from the passenger section, and the two were connected by a telephone apparatus. Three large windows were in each wall, which was slightly curving near the ceiling. At the rear was a large compartment for food, maps, and other equipment.

“Now that you’ve looked it over, how would you like to go up for a short ride?” the aviator asked, as the others examined the ship minutely.

“Like nothing better!” came from Bob. “Can we go now?”

“Yeah. Everybody hop in. Be sure that door’s tight.”

Delighted at such an opportunity, the youths and Mr. Wallace took places in the cabin, while Karl climbed into the cockpit.

A few seconds later there came the roar of the motor, and then the passengers felt themselves moving.

The ’plane rolled over the cement runway for several hundred feet, then gradually left the ground and began climbing steadily.

“We’re in the air!” cried Joe excitedly. He and his friend had never been in a monoplane before. “Doesn’t feel unusual, does it?”

“I wouldn’t know it if I didn’t see the ground dropping away from us,” Bob said. “We’ll probably appreciate the absence from jolts and jars.”

This easy conversation was made possible by the heavy insulation between the pilot’s and passengers’ quarters. As a result, the roar of the engine was silenced to a remarkable degree.

When just above the airdrome, they heard Karl’s voice through the telephone.

“How does it feel?” the aviator asked. “Think you’d like flying?”

“Sure,” came from Joe, speaking through the transmitter. “It’s a hundred per cent better than land traveling.”

The experience was not novel to Mr. Wallace, who had once crossed the continent in a huge tri-motor monoplane. But nevertheless he appeared to be enjoying it as much as the young men.

An altitude of perhaps a thousand feet was reached, and then the ’plane shot ahead toward the business district of Washington.

They had been in the air perhaps five minutes when Karl’s voice was again heard through the telephone.

“See anything familiar below?”

“By George!” exclaimed Bob wonderingly. “We’re right above our houses. Suppose anybody sees us?”

“Guess not,” his chum said. “They’re not out, anyway.”

A much higher altitude was reached, and their direction of travel was changed.

From that height, the passengers could easily make out the business district, including the United States Capitol, the White House, and other government buildings. In addition, they could see several score miles in every direction.

“Isn’t that Baltimore over there?” queried Joe, his keen eyes scanning the landscape.

“It is at that,” observed Mr. Wallace. “The atmosphere isn’t any too clear, though, and we can’t make it out very plainly.”

“We’re a great distance away, too,” remarked Bob. “Wonderful when you think about it, isn’t it?”

They circled around for a few minutes and then headed back to the airport, as the aviator did not care to use too much gas.

When again on the ground, Bob and Joe were more anxious than ever to be among those of the expedition who would travel by air. Their eagerness was increasing with every minute.

“You’ve got to let us go!” said Bob to his father, when he and his friends had returned home. “Why, just see what we’ll be missing if we don’t.”

“You may be missing death,” Mr. Holton returned grimly. “But then,” he went on, raising his voice, “the chances are that nothing will happen. Any more, airplane accidents are rare. I’ve almost decided to go myself. It will be a chance of a lifetime.”

“Then—then you mean we can go?”

“I haven’t exactly said so,” the naturalist answered. “There is your mother, don’t forget.”

“Perhaps she won’t consider it so wonderful,” suggested Mr. Wallace, who had been induced to spend the few days before leaving with the Holtons.

Bob’s mother did not at all like the idea when it was put before her later. But she did not protest so violently when she saw that her husband was actually bent on going. After all, his judgment had seldom failed him, and most likely would not now. Then, too, she was somewhat of an air enthusiast herself, having great faith in the development of aviation. And what Mr. Holton did she usually considered fit for Bob.

Joe had more difficulty in securing the consent of his parents, for they were doubtful as to the outcome of such a venture. Mr. Lewis, however, was well acquainted with Karl Sutman, and knew him to be an excellent airplane pilot, besides being a resourceful, well-thought-of citizen. In the end, Joe’s parents consented to the youth’s going, especially when they learned that Mr. Holton and Bob intended to go. Mr. Lewis, however, had already booked passage on a steamship, and could not cancel his arrangement, much as he would have liked to.

The two chums were delighted beyond words.

“It’ll seem strange without your father with us, though,” said Bob. “We all went together on our other trips, and——”

“He’ll meet us in Mollendo,” Joe reminded him, and then added: “Wonder if Mr. Wallace will go in the ’plane?”

That person desired very much to do so, but hesitated to let Mr. Lewis make the ocean trip alone. Joe’s father, though, declared he would not be without companions, for he was acquainted with several members of other divisions of the expedition. A Mr. Thomas L. Wells, of the division of ethnology, was a very close friend of the naturalist.

“So, although I would like for you to come with me on the boat, I want you to go in the airplane,” Joe’s father said to Mr. Wallace, “because I know you are bent on doing so, and it is a wonderful opportunity.”

The result was that Mr. Wallace made preparations to go by air, much to the delight of Bob and Joe. Since their first meeting with the naturalist several months before, the youths had taken a great liking to him.

Making ready for the airplane trip was a novel experience to Bob and Joe. They found there was much to be purchased in the way of suits, caps, goggles, and other provisions. Aviator’s togs, the young men knew, would not be strictly necessary, as it was a monoplane with a closed cabin. But they thought it best to get them, since they could also be used for general outdoor clothes.

“Here’s something the express man left you, boys,” Mr. Holton called, when the chums returned from a shopping trip downtown.

Eagerly Bob and Joe opened the large box. A minute later, when they saw its contents, they uttered exclamations of joy.

“The moving-picture camera and film, from the Neuman Motion Picture Corporation!” cried Bob happily. “It got here just in time, didn’t it? We’ll be leaving day after tomorrow.”

The Neuman Motion Picture Corporation, a large firm that released educational films, had engaged the services of Bob and Joe on their two previous expeditions. The youths took moving pictures of the strange lands they visited, and so pleased the film company that they were given the opportunity of again taking moving pictures while in the Andes Mountains. Always the boys were paid a substantial sum for their trouble, which to them was sheer pleasure.

“Inca land you’ll find to be perhaps the most interesting place you’ve photographed,” Mr. Holton told them. “If you do this well, the company will almost eat you up in their praise of you.”

“The Inca empire is still sort of a mystery to me,” said Joe. “I’ve read quite a bit about it, and Mr. Wallace and Bob and I saw that movie in Chicago, but it’s still all not quite clear. I know how the country around there looks. It is the empire itself that I don’t know much about.”

“Not being an archæologist, I don’t know a great deal about it,” Mr. Holton said. “Perhaps not much, if any, more than you fellows. I do know, though, that the Incas maintained a socialistic state, in which everyone was forced to work on a given piece of land without deriving any direct benefit. The grain that they raised all went to a common storehouse, and everyone drew from it in times of stress.”

“A sort of depression insurance,” laughed Joe.

“Might call it that,” the naturalist said with a smile. “At any rate it seemed to prove effective.”

“How about the wild animals and birds in Peru?” asked Bob. “Are there many there?”

“Now you’ve mentioned a subject that I know something about,” returned Mr. Holton. “Yes, there are countless numbers of interesting wild creatures in those mountains. Most impressive of all is perhaps the condor, the largest bird that flies. We naturalists wish particularly to investigate reports of a species of condor that is pure white in color. Whether we’ll find it we have yet to see. But there are other birds and animals that we feel sure of getting, such as the puma, armadillo, lizard, guanaco, fox, and snipe. We aren’t allowed a great deal of time in the Andes, but we feel certain that a large number of wild creatures will fall at the report of our rifles.”

The next two days were busy ones for Bob and Joe. They frequented the business district often to get minor articles that they would need on the trip, and by the time the great day of leaving came they had finished all preparations.

After breakfast Mrs. Holton and Mr. Lewis drove the leavetakers to the airport. When they arrived at that place they found that an expert mechanic had just completed a thorough inspection of Karl Sutman’s monoplane, and had found it in perfect running order.

Their belongings were all placed in the provision compartment, and then, with sincere farewells, the youths, Mr. Holton, and Mr. Wallace climbed into the cabin, while Karl took his place in the cockpit.

The engine was started, and then, after the travelers had called out one last farewell and promise to be careful, the monoplane rolled heavily over the concrete runway and pointed its nose toward the southern sky.

“We’re off!” cried Joe excitedly. “Off for the Andes Mountains!”

---

AS the monoplane rose higher, Bob and Joe and the others waved to the little group below until it faded from view. Then they turned to take in the country they were passing over.

Streets, buildings, vehicles, and people were mere specks below, as Karl sent the machine to a new high altitude. Past the city of Washington, and then on—on above the many small cities and towns of southern Maryland.

“Wonderful view!” breathed Joe Lewis, gazing out at the wonderful panorama that was spread out before them.

“Bet we can see fifty miles,” added Bob. “There’s the Potomac River over there, and away off in the distance seems to be the ocean. I wonder if it is?”

Bob and Joe were strangely unaware of forward movement, though they were going nearly twice as fast as the fastest automobile. The comfortable enclosed cabin kept out the fierce roar of the wind, and heavy insulation silenced the noise of the engine to a remarkable degree. Thus they found it easy to carry on conversation.

They made the hundred-and-forty-mile trip to Norfolk in little more than an hour. Then, after leaving this city behind, they passed over North Carolina until finally the ocean loomed up before them.

When the last stretch of land had been left behind, Bob and Joe were thoughtfully silent. What if anything should happen while they were out here above the boundless water, with no place near on which to land? It was not pleasant to think of plunging hundreds of feet into the ocean, even though the water might be calm.

As they flew farther, Joe was surprised that they had not seen ships below them.

“This isn’t a route of travel,” explained Mr. Holton. “We probably won’t see any large liners till we get farther south.”

Later they were able to make out several tramp steamers, which, when viewed at that altitude, appeared to be at a standstill. Just where the vessels were heading the air travelers could only guess.

Suddenly, unexpectedly, the youths and the naturalists found themselves in a heavy cloud, which hid the ocean from view. It was so dark that Mr. Wallace almost mechanically switched on a light.

“Wonder if this means danger?” mused Joe, gazing intently out of the window at the haze.

“I was wondering the same thing,” came from Mr. Holton. “If it does, we ought to hear from Karl before long.”

But before long they passed out of the cloud and once more could see the ocean. But now the sun was nowhere in sight.

“We may have some rain,” said Karl through the telephone. “Be sure all the windows are closed tightly.”

Bob wondered if rain would be a hindrance to flying, although he hesitated to put the question before Karl. If the truth were known, he was not a little worried.

As they flew farther the sky became more overshadowed. Dark, threatening clouds hovered near, as if to warn the air travelers to seek a place of refuge. It was not a pleasant sight to the four passengers.

All at once they had a sudden sensation of falling, which almost took their breath away. It lasted but a brief moment, however, much to the relief of all.

“What caused that?” asked Joe, who had turned pale.

His question was answered a little later by Karl.

“Feel that drop?” the aviator asked. “I did that to see if we can’t get below the storm area.”

“How far did we fall?” inquired Mr. Wallace interestedly.

“Only a few hundred feet. And I steered over to the east, too. We seem to be out of the storm area.”

Now, as they flew on, the travelers could easily glimpse the dark mass of clouds that they would have been forced to pass through had they remained strictly on their course.

An hour or so before noon, the explorers caught sight of a little group of islands, and in the distance they could make out one that was much larger.

“We’re nearing the West Indies,” observed Mr. Wallace jubilantly. “That large island away over there is probably Abaco.”

As they neared the land, Karl dropped to perhaps a thousand feet. From this altitude they could command a good view of the country below them. It was for the most part wild and uninhabited. There was a great deal of fog hovering about, or they could have seen many more islands.

They were nearing the tropics, as evidenced by the mercury rising in the thermometer. As they were traveling evenly, it was safe to open the windows. The resulting gush of wind was at once greatly appreciated.

“We’ll have about three hundred and seventy-five miles of traveling before we reach Cuba,” announced Karl, as they passed over a large cluster of islands. “Maybe we’d better land there, at least for a few minutes. It’ll give the ’plane a chance to cool off, and then, too, we can look it over.”

It was three hours later that Bob caught sight of what appeared to be a long black line stretching out of sight to their left. That line gradually took shape and color, and the explorers found themselves nearing Cuba.

On the side nearest them was a large mountain, with a cone-like top that gave it the appearance of a volcano.

Within sight of this peak, Karl picked out a level stretch of ground and sent the monoplane downward. He found it necessary to make a spiral landing, as there was danger of otherwise striking a line of low, sharp peaks.

Bob and Joe watched closely as the ground came up to meet them. Then they felt the wheels bump, and they knew they were safe.

“All out!” called Karl, appearing at the cabin door. “That is, if you want to rest your legs.”

The others needed no urging. They climbed stiffly out of the ’plane and stretched freely. While they had not been cramped, they had nevertheless not been allowed the freedom of violent exercise.

“So this is Cuba,” observed Joe, yawning and looking at the green jungle, which seemed everywhere about them.

“Not much to be seen in this part of the island,” Mr. Wallace told them. “We’re at the extreme eastern end.”

They looked around a bit, though, to satisfy their curiosity.

When they finally returned to the ’plane, after taking a tramp toward the high peak, the explorers were ready to devour anything in the way of food.

Sandwiches and iced tea, the latter having been kept cold in a thermos jug, served as a meal, and proved to be very satisfying to the hungry explorers.

Then, after taking a short rest in the shade of the monoplane, they prepared to resume the journey.

“Now comes the worst part,” said Karl, with a frown. “We’ll have to fly for over five hundred miles without seeing a trace of an island. The Caribbean Sea may prove treacherous for tropical storms, too.”

Luck was with them the first half of their trip. The sky remained clear and light, not giving the slightest indication of a change of weather.

Then suddenly, when the travelers’ hopes were high, they noticed that the sky was becoming dark and threatening. A fierce wind was blowing with a dangerous velocity, which threatened to send the monoplane off its course.

Karl guided the machine off to the west, in the hope of passing beyond the storm area. He speeded up to over a hundred and fifty miles an hour, for he knew that whatever he did must be done quickly.

But try as he did, he could not escape the heavy clouds and terrible wind.

His hope almost gone, he sent the ship to a much higher altitude, thinking it might be possible to get above the clouds.

But it was too late. With a rush and a roar, the tropical hurricane was upon them.

---

NEVER in their lives had the explorers witnessed anything like the terrible onslaught that followed. The violent, ruthless wind dashed the monoplane about dangerously, threatening at every moment to tear it to pieces. It was but a frail, man-made machine when caught in those forces of nature.

Karl’s ability as a pilot promised to be tested to the utmost. If he could keep the ship straight it would be nothing short of miraculous. The less skillful aviator would send his craft dashing down to the foamy water below. But Karl was by no means a novice. He had had wide experience in piloting passenger monoplanes on schedule across the United States.

“Sit tight!” he called through the telephone, suspecting that his friends were frightened. “We’ll get out some way—I hope.”

Every gust of wind tossed the ’plane about hazardously. It seemed that a plunge would be inevitable.

In the cockpit Karl Sutman was determined to bring his friends and himself safely through the danger. With nerves of steel, he hung on desperately to the stick and the rudder bar, keeping his keen eyes glued to the horizon.

It was indeed a race between life and death, as the staunch ’plane was swung about at the mercy of the storm. Many times before had the machine proved itself capable of withstanding the assault of the elements, but this was the supreme test. If it could weather this, it would indeed be a strong machine.

Inside the cabin, the youths and the naturalists were pale with an awful fear that this would be the end. They could not conceive of passing safely through such a hurricane as this. They were only too aware that many an aviator had gone to his doom in a tropical storm.

Now, to add to the terrible scene, a heavy rain began to fall, coming in great gusts with the wind. It pattered ominously on the wings, bearing the monoplane down with the added weight.

“Oh!” groaned Joe, almost giving up in despair. “I suppose the worst is yet to come.”

“Cheer up,” said Mr. Holton, who was inclined to be hopeful, as he noticed that the wind was blowing more evenly. “It can’t last so very much longer.”

Despite this expression of optimism, the hurricane continued at full force, although a bit smoother than at first. Now the wind, instead of coming in great gusts, blew steadily.

This made it slightly easier to handle the ’plane and took some of the severe strain from Karl. But he still was forced to use all his energy in keeping the craft at as even keel as possible.

All knew that a tropical storm was usually over a wider area than one in the temperate zone. It was this that had made it impossible for Karl to steer the ’plane to safety before the gale struck.

Only gradually did the monoplane pass through the clouds, which extended many miles in every direction.

Finally, when a clear sky again became visible, the explorers uttered cries of relief. They had at last escaped what seemed like certain disaster.

Bob moved over to the transmitter.

“You were wonderful, Karl, old boy!” he praised. “If most anyone else had been in your seat, we wouldn’t be in the air now.”

“Oh, there are plenty others that could have done it,” the aviator returned, his voice sounding a bit nervous. “I just saw that I had to get out some way and did everything I could.”

The storm had served in no small measure to heighten the explorers’ admiration for their pilot. If the latter could safely guide them through such a display of the elements, he could be depended upon for almost any crisis.

The brilliant sun was now rapidly showing itself in full view, casting a sparkling reflection on the ocean. All evidences of the storm were covered up, even the heavy foam caps having disappeared. It was as though nature were repenting of her arduous activities.

As they flew on, the explorers had a strong hope that the weather would remain calm during the remainder of their journey. They were nearing land now, and they wished to finish the trip in a cloudless sky.

At last, when they were becoming weary from seeing nothing but boundless water, they suddenly caught sight of a dim shape that covered the whole of the horizon. That shape became larger and more plain, until it took on the form of land.

“Hurrah!” cried Bob joyfully. “South America at last!”

“I believe you’re right,” came from his father. “It——”

“Announcing our arrival at the great continent of South America!” Karl’s voice, coming loudly through the telephone, broke off with a laugh.

As they came nearer, the aviator guided the machine to a lower altitude, although still high enough to see many miles in every direction.

But it was a long while before they could make out plainly the details of the coast. Fog made it necessary to fly very near in order to see anything distinctly.

“I believe I can make out the Andes,” said Joe, gazing out at the distant horizon.

“Don’t be sure,” laughed Mr. Wallace. “Those mountains are a long way off.”

Before long they had passed the coast and headed over the land, almost directly above the Magdalena River, whose course they could easily make out.

For the most part, the country they were flying over was rugged and uncultivated, but there were occasional towns and villages that dotted the valleys and clearings.

“Bogotá is the first large city we’ll see,” announced Karl. “We ought to get there by tomorrow noon.”

“Where will we spend tonight?” asked Joe, as he noticed that darkness was not far off.

“Suppose we land before long and put up our tent,” suggested Mr. Holton, stepping up to the telephone transmitter.

“I was just getting ready to do that,” Karl answered him, and then added: “Here’s a good spot now.”

There was a wide, level field directly below them. Karl sent the monoplane off to the west and then headed it back and downward.

A perfect three-point landing was made in the tall grass, the ship coming to a stop at the very edge of a frowning jungle.

Once more the explorers got out and stretched their legs.

Bob and Joe had just started over to the jungle when they heard something that made them turn about quickly.

“There’s a leak in the gas tank,” Karl said ominously, “and the gas is almost gone. We landed just in time.”

---

AT Karl’s dread discovery the others uttered exclamations of alarm and astonishment.

“What could have caused it?” asked Bob grimly.

The aviator shook his head.

“Can’t say,” he returned. “Maybe something pierced it while we were in Cuba. Could have made a small leak that let out a little at a time. Or the storm could have done it.”

“Good thing we were able to make it across the Caribbean,” remarked Mr. Holton. “If it had been much larger, perhaps we wouldn’t be here now to find it out.”

The short-lived tropical twilight was upon them, with a promise of darkness being only a few seconds off.

“Suppose we put the tent up while we can see to do it,” suggested Bob. “Then we can attend to the leak in the morning. There’s some solder in the provision compartment, and we can put some of it on now to keep the remainder of the gas from running out.”

The others thought this good advice. While the youths and the naturalists made camp, Karl Sutman applied a heavy coat of liquid solder over the cut in the gasoline tank.

“I guess we’re in a mess,” the aviator said disgustedly. “We’ve used up all the gasoline in the spare tank, and now we haven’t enough to take us twenty-five miles. We could have flown to Bogotá easily if it hadn’t been for that leak.”

“Bet there isn’t a gasoline station within fifty miles of here,” groaned Joe, glancing at the rugged country that was on all sides of them.

Darkness overtook the explorers before they had completed making camp. They were forced to turn on the lights of the monoplane until they could gather sufficient twigs for a fire.

When finally a roaring blaze illuminated the sky, they turned to complete making the camp.

As a precaution, this was made on a spot several hundred feet from the monoplane. This would do away with the danger of an explosion, for the intense heat from the fire might easily have ignited the remaining gas in the tank.

“Now to get a meal,” said Bob, edging closer to the blaze to escape the chill of the tropical night.

A delicious spread of food was prepared, all eating heartily. The eventful day had stimulated their appetites highly.

“I suppose there’s no use worrying,” grunted Karl, stretching out before the fire. “We’ll find a way out somehow. If we can’t do anything else, we can all hike to a town and carry back enough gas to carry us a short distance. Then we can hike to another town, and do the same thing over again.”

“Do these towns around here have gas, though?” came from Joe. Despite Karl’s expression of hope, he feared the worst.

“That we don’t know,” Mr. Wallace said. “It may be there hasn’t been an internal-combustion engine in this region for years, if at all.”

A rapidly growing exhaustion made the explorers for the time being forget their cares and curl up in the tent, after having heaped the fire high with fresh fuel. They had not thought it necessary to stand guard, as there was probably nothing in this region that would bother them.

The next morning Karl got out a map of South America and spread it out on the tail of the machine.

“Here we are about twenty miles inland,” he said. “The nearest town appears to be about fifteen miles from here. Luckily it’s south, and we won’t have to go much off our course.”

“Think we can get gasoline there?” queried Joe.

“Probably not,” Karl answered. “But if we have to we can take a train to Cartagena—that’s a city not far from here on the coast. Of course they have gas there.”

They climbed into the monoplane, which, with a roar, rolled over the high grass and headed south. Karl kept the machine going at as slow a speed as possible, for he desired to use every ounce of fuel to advantage. But even then they made the short trip to the little town in but a few minutes.

“Here we are, right near the town.” Karl climbed out of the cockpit after having made a perfect landing.

Scarcely had the explorers stepped to the ground when they caught sight of a score or more natives running toward them. It was a motley crowd that surrounded the Americans a few seconds later.

Surprise, bewilderment, amazement were displayed on the faces of the Colombians. The monoplane they viewed with a certain awe that was almost childish in its sincerity.

As soon as the jabbering had abated somewhat, Mr. Holton addressed them in Spanish, asking if it might be possible to procure gasoline for the airplane.

The faces of some were expressionless, but a few shook their heads.

“We do not use gasoline here,” one man said in the native tongue. “There are no great birds like this”—pointing to the monoplane—“in our land. And we have no carriages that are not drawn by animals.”

Mr. Holton then asked if it might be possible to get gasoline in Cartagena, the city on the coast.

Strange to say, the people did not know. Evidently they had never been to that place, although it was less than fifty miles distant.

“Well, then,” began Karl, “I suppose one of us will have to take a train to Cartagena. Whoever goes can take a gasoline can with him and get it filled. Then he can return on the next train.” The Americans could not help laughing at this, however necessary it might have been. The idea of boarding a train for a fifty-mile journey merely to get a can filled with gas seemed provoking.

“What a predicament!” roared Bob, catching hold of the monoplane in order to hold his balance.

“I suppose we ought to take this more seriously,” said Karl, who was also laughing. “But somehow it all seems humorous to me.”

At sight of the Americans laughing, the crowd of natives looked about sullenly. No doubt they thought the newcomers were making fun of them. Finally one man stepped up to Bob, and, with a sneer, uttered something in the native language.

The youth could only catch a word or two, but it was enough to make him glare at the man in anger.

“Be careful, Bob,” warned his father. “There are too many of them for us to get into a scrap.”

“Aw, I could lick them all with one hand!” snarled the youth, his eyes resting fearlessly on first one and then another of the men.

He was able to control his temper, however, and as the Colombians made no further move, he turned to Karl Sutman.

“Why can’t I make that train trip?” he asked. “I’ll pay my own fare. Really I’ll enjoy it.”

“All right,” came from Mr. Wallace. “And I’ll go with you. It will take two to carry the gas can when it’s full.”

“Be careful,” warned Mr. Holton. “We won’t be surprised if you’re gone a day or two.”

At the railroad station, which was little more than a mud hut, they found that a train would arrive in less than three hours. They thought it best to remain near the depot, for the schedule might not be accurate.

The train finally came, but, much to their disgust, the two gas seekers were informed by the conductor that they would arrive in Cartagena no sooner than four hours later.

At last they started moving and slowly left the station behind. The little crowd that had assembled to see the train off waved a farewell as it disappeared around a curve.

Bob and the naturalist gazed intently out of the window at the barren country they were passing through. Only at intervals could they make out an adobe house.

They had gone perhaps an hour when they were startled by a sudden commotion at the head of the train. Bob was looking out of the window trying to make out what was going on when he suddenly felt the train come to an abrupt stop.

Wondering what was meant, he and Mr. Wallace had started toward the front of the coach when they were interrupted by a cry that echoed through the train.

“We’re being robbed!” exclaimed Mr. Wallace, hurrying back to the seat. “There’s a gang holding up the train!”

---

“ROBBED?” cried Bob, almost unbelievingly.

Before he could say anything further, a tall, dark man appeared at the front of the coach. Roughly he shouted something in the native tongue, at the same time flashing a shining pistol in full view of all.

“Quick!” exclaimed Mr. Wallace, taking advantage of an opportunity. “Hide our money—under the seat there next to you.”

The naturalist handed his pocketbook to Bob, who had taken his own purse from his pocket. The two he placed in a little crack between the seat and the side of the coach.

He was not a moment too soon. Scarcely had the youth resumed his natural position when the robber appeared before him and demanded money.

“Our pockets are empty,” Mr. Wallace told the man. “You can’t get anything from a poor man.”

The Colombian soon found that the naturalist spoke the truth. But even then he was a bit suspicious. Americans or Europeans—he knew not which they were—usually were rich, carrying with them much money. And that these two had boarded the train with empty pockets was indeed surprising.

Search as he did, however, he could find no trace of any money. But he was somewhat satisfied when he took possession of Mr. Wallace’s handsome watch.

Luckily Bob had left his timepiece in the cabin of the monoplane, having forgotten it in the excitement of the day. Strange to say, this was the first day in the week that the youth had not worn it.

“Well,” said Mr. Wallace, after the man had gone, “I lost the equivalent of fifty dollars. Not a great deal. But too much to have taken from me.”

“Good thing you thought to mention hiding our pocketbooks,” Bob told him. “If you hadn’t, we’d have been in a fine mess. Away out here in a strange country with no money.”

“And of course the railroad wouldn’t have made it good,” the naturalist said disgustedly. “If I ever have another watch I suppose I’ll have to pay for it.”

Ten minutes later the train was again chugging across the barren plateau. The robber gang had vanished before a cloud of heavy dust, perhaps not any too well satisfied with its exploit.

“I didn’t know this was dangerous territory,” remarked Bob Holton a little later. “Seemed like everyone was too lazy to do anything but loaf.”

“I guess we’ll find gangs anywhere we go,” Mr. Wallace told him. “At least that’s my opinion, after quite a bit of traveling.”

Bob recalled the bands of criminals he had met with at home and on the Sahara Desert, and concluded that his friend was right. No matter how much good there is in the world, there is always a certain amount of bad.

Two hours later the Americans were surprised to see that they were coming into a town. At the railroad station where they had boarded the train, they had not been told that another town was between them and the coast.

“This is Mahatos,” announced the naturalist, pronouncing the name as best he could.

“Guess everyone here wants strangers to be sure and know what town they’re in,” laughed Bob. “At any rate, that sign is plenty large. Almost hides the station.”

This town was much the same as the one at which they had boarded the train. They were glad when finally it was left behind.

“Wonder if we’ll make any more stops?” mused Bob with a smile.

“Don’t be surprised if we do,” Mr. Wallace replied. “For all I know there may be a dozen villages between us and the coast.”

During the next two hours the train crawled along without coming to a settlement. Then finally it passed a row of little black houses and pulled into Cartagena, the coast city.

“All out,” said Mr. Wallace, picking up the large gasoline can. “We’ve reached our destination at last.”

As the Americans looked about the well-built station, they found that this was a city of considerable importance. Crowds of people, clusters of business houses, and—what was more interesting to them—automobiles dotted the streets.

“Where there’s a motorcar there’s gasoline!” cried Bob joyfully. “Now who says we won’t put fuel in the airplane tank!”

They found a filling station—or at least a place where gasoline was sold—not far away and lost no time in having the can filled to capacity. Then they turned back to the railroad station.

“Our business in this city is completed in five minutes, after having made a four-hour trip here!” Bob could not help bursting out in laughter, and Mr. Wallace joined him.

They entered the railroad station and inquired when they might board a train back to Calamar.

Much to their displeasure, they found that it would not be possible to do so until the next morning. The agent explained that it was necessary to repair a portion of the track, and that until this was completed, a run could not be made.

“Just as I expected!” groaned Bob, sitting down on the seat hopelessly. “To save your neck you can’t make time in South America.”

“What will we do to while the time away?” asked the naturalist.

“Look around, I suppose. Nothing else to do.”

The Americans found Cartagena very interesting. Its several industries were throbbing with life; its people were possessed of a certain amount of energy and ambition that was entirely absent farther inland.

The travelers were loitering along at the port, watching the steamers arrive and depart, when Bob suddenly caught sight of something that caused him to nudge his friend.

“Look at that fellow over there,” the youth pointed out. “Isn’t he an American?”

Almost at once Mr. Wallace made a reply. “He is as sure as I’m born. Or else”—the naturalist hesitated—“he’s English.”

The object of their remarks was a short, fat young man of perhaps twenty, with twinkling eyes and a pug nose. He was dressed in khaki outdoor clothes that stretched tightly over his protruding stomach.

Before Bob and the naturalist could make a further move, the strange young man walked over to them, his small, deeply set eyes flashing with merriment.

“Ain’t you from the good old U. S. A., or ain’t you?” he demanded, extending a short, fat hand.

“From nowhere else!” Bob was overjoyed. “And I take it that you are?”

“Right as four chipmunks!” the little fellow said quickly. “You’re lookin’ at Chubby Stevens, from Houston. And now that I’ve got that off my chest, I ain’t expectin’ you to hold your names a secret.”

Bob laughed.

“This is Mr. Wallace, and my name’s Holton—Bob Holton. I’m from Washington and my friend’s from Chicago.”

“A good bit of the Estados Unidos is represented here, I see,” Chubby said with a laugh. “The East, Middle West, and Southwest. I suppose you’re just lookin’ around?”

“For the present, yes,” Mr. Wallace returned, and then related the events that led to their being in Cartagena.

The fat youth listened intently.

“You may be wantin’ more of South America, but I don’t,” he said when the naturalist had finished. “I’ve been here a year and have got all I want of it. I’m longin’ to see the old Gulf Building, back in Houston. Dad’s office is there. He’s a lawyer.”

“And you—what are you doing here, just seeing the country?” inquired Bob.

“I’m seein’ too much of it to suit me,” Chubby answered. “Came here to look around and to get rid of some fat. But doggone it, I’m fatter now than I ever was. Guess I’ll have to cut out adventurin’ and take back my old job in the office, if I want to get skinnier.”

A burst of laughter followed.

“You’re hopeless, all right,” chuckled Bob. “I never saw a case like yours before. Why, I weighed a hundred and eighty before I left the States, and I’ll bet I don’t weigh much more than a hundred and seventy now. If exploring would do that to me, why won’t it do it to you?”

“That’s what I’ve been tryin’ to figure out for the last year,” Chubby returned. “Funny, but I used those same figures, but I just switched them around. Went from a hundred and seventy to a hundred and eighty. That’s away too much weight for a bozo my size to carry around.”

“Why don’t you try swimming back to America?” laughed Bob. “That might do the trick.”

“I’ve been thinkin’ about that, too, only I’m afraid I couldn’t take along enough to eat.”

“Oh!” Bob groaned hopelessly, and then, as he found that Chubby had just arrived in Cartagena, suggested that they take a walk about the city.

But as it was almost noon, Chubby suggested that they get a “bite” to eat. Just enough, he said, to prevent them from falling from hunger.

Mr. Wallace snorted.

“I suppose it’s impossible to do it,” the naturalist said earnestly, “but I’d like to take you along on our expedition into the Andes. If you’ll go, I’ll guarantee that you’ll get rid of twenty pounds.”

“Huh? Are you tryin’ to kid me?” Chubby looked up suddenly.

“Not a bit of it,” Mr. Wallace answered, trying hard to suppress a smile. “It works every time. You see, we have to get by on limited rations and——”

“Fine! I’ll go—— What was that you said? Limited rations? That means less food, doesn’t it?”

Mr. Wallace nodded.

“Then I’m afraid,” began Chubby, shaking his head slowly, “that I couldn’t think of considering your proposition, however wonderful it might be. I’m——”

“It’s no use,” laughed Bob. “A heavy eater doesn’t make an explorer.”

Bob and the naturalist were finally persuaded to follow the fat youth’s suggestion and get a “bite” to eat. Then they continued their sightseeing.

Thus the remainder of the day passed, and they began to look about for a place to spend the night. Chubby resolved to remain with his newly found friends as long as the latter stayed in Cartagena. Then, he told them, he would take a boat to the United States.

The three Americans engaged a small room in a boarding house that was owned by a Canadian. Although it was not the utmost in comfort, they were glad to throw themselves on the hard bed to retire.

They passed a restful night, however, awaking late the next morning.

“What shall we do until train time?” asked Bob, preparing to leave the room.

“Look around some more, I suppose,” Chubby said. “In this country you can always find something you haven’t seen before. There’s a lot that’s funny, too. I’ve been laughing a year at the natives.”

“Maybe they’ve been laughing at you,” Bob thought to himself, but said nothing. The fat little fellow would indeed provoke a smile from many.

Until ten the three walked around the city, noticing everything that was peculiar to this strange land. When finally they came back to the railroad station, they were not a little fatigued. Especially tired was Chubby.

“Well,” Bob began, “we’ll leave in fifteen minutes, if we follow the set schedule. I suppose,” he said to the fat youth, “you’ve definitely made up your mind to go back home?”

“Yeah.”

“Then you won’t think of going with us to the Andes? We could use you, all right.”

“Sorry, but it’s North America for me.” Chubby spoke decisively. “This continent here ain’t fit for a gazook like me. I want to get back.”

He exchanged addresses with Bob and Mr. Wallace, pocketing his notebook just as the train steamed up to the station.

“Good-bye and good luck!” called Bob, as he stepped up into the coach. “Write us sometime.”

“Hope you lose some fat,” laughed Mr. Wallace, as they started moving. “And you’d better not try to swim to the U. S.”

The train moved slowly away, leaving Chubby to stand on the platform, still waving.

“Good fellow, all right,” smiled Bob, settling himself down in the seat. “All he needs is a little well-directed exercise.”

“I’m afraid he won’t get it,” said the naturalist. “He’ll probably be fat as long as he lives.”

The journey back to Calamar was uneventful. Bob and Mr. Wallace looked out rather fearfully as they passed the spot where they had previously been robbed. But no gang appeared this time to stay them.

Finally they reached their destination and left the train. They were greatly surprised to see that no one was there to meet them.

“That’s funny!” mused Bob, as he and the naturalist lugged the heavy gasoline can in the direction of the airplane. “I thought sure Dad or Joe would be here.”

When at last they came to the airplane, Bob gave a cry of surprise.

Seated on the ground were Joe, Karl Sutman, and Mr. Holton, their faces bleeding from numerous scratches, their clothes torn and wrinkled.

---

“FOR the love of Mike!” cried Bob Holton. “Whatever happened?”

“Plenty!” came from Joe quietly. “We had a fight.”

“A fight?” Mr. Wallace was perplexed.

“Yes, and a big one at that,” said Karl grimly. “But we licked them.”

“Licked whom?” demanded Bob, becoming impatient. “Come on. Tell us about it.”

Mr. Holton got to his feet.

“Look over there,” he directed, pointing to a spot near the tail of the monoplane.

Bob and Mr. Wallace looked.

Lying prone on the ground was a man, a native Colombian, evidently still dazed from a blow. He made not the slightest move, although it was apparent that he was not hurt seriously.

“Karl knocked that fellow out,” explained Bob’s father. “In addition to being a fine aviator, that fellow’s a fighter.”

Bob glanced at Karl. From the start the youth had believed the aviator could give a good account of himself if called upon.

“But that’s not telling us anything,” said Mr. Wallace. “What caused the fight? How did it all come about?”

“This way,” began Mr. Holton. “Joe and Karl and I were sitting in the cabin of the ’plane discussing the expedition when we were suddenly interrupted by a gang of at least five rough men, who rushed at the ’plane angrily. We didn’t know what their object in attacking us was, and never did find out. Perhaps they wanted to steal what we have, or they might have been in that crowd yesterday when we laughed and they thought we were making fun of them. At any rate they came at us furiously, and one man broke out the glass in a window. We got out of the airplane as soon as we could to defend ourselves. We couldn’t get to our guns because they’re in a nailed box. But we used our fists to good advantage and finally were able to beat them off. All got away but that fellow over there.”

“Well, of all things!” exclaimed Mr. Wallace. “Seems like we’re having trouble and then more trouble. Bob and I had an experience on the train that wasn’t very pleasing,” he said, and then told of the robbery in which he had lost a valuable watch.

“We’ll soon be out of this country, I hope,” sighed Joe. “Though I suppose it isn’t the country so much as it is our stroke of bad luck.”

“No,” agreed Bob. “Anyone——”

He stopped quickly, as he observed that the Colombian who had been knocked out was regaining consciousness. At first the man merely stirred about, as if totally unaware of what had happened. Then he glanced up and got to his feet.

Pausing but a moment to glare at the Americans, the man dashed away in the direction of the town, drawing his teeth back in a wicked snarl as he looked back at them one last time.

“I think we’d better get away from here as quickly as we can,” said Mr. Holton. “For all we know there may be another gang getting ready to attack us. The whole town might even come out.”

His remark served to set Karl Sutman to action.

“Let’s get the gas in the tank,” he suggested, walking over to the can that Bob and Mr. Wallace had brought filled from the city on the coast.

Together, Joe and the aviator lifted the heavy can up and poured out its contents. Then, after making the cap secure, Karl climbed in the cockpit and switched on the engine.

“This will take us from fifty to seventy miles—maybe farther, depending on how fast we fly,” he told the others, as they entered the cabin and snapped the door shut.

As they left the ground, Joe noticed that they were heading west. He wondered what was the meaning of this, since Bogotá, which was south, was their goal.

“I’m going to find out,” he thought, and, stepping over to the transmitter, he put the question to Karl.

“I decided all at once to go over to that coast city—Cartagena,” the aviator answered. “There we can fill both our tanks to capacity and won’t have to worry any more. Otherwise, if we merely used the gas that Bob and Mr. Wallace brought, we might find it necessary to hunt up another town that has gasoline.”

“You think of everything,” praised Bob’s father, moving up to the transmitter.

“I’ve decided to make another change, too,” Karl said with a laugh. “I think it might be best to miss Bogotá by a hundred miles and head at once for Lima, the capital of Peru. We can stop at Quito, the capital of Ecuador, for more gas, and then continue on to Lima. Here we’ll again land to fill our tanks. After that we’ll go on to—well, perhaps to Cuzco, if we want to look around a little before Mr. Lewis gets here by steamship. How does it sound?”

“O. K.,” said Bob quickly, and then, with a sudden thought, added: “How about the tank that leaks? Can we have it repaired in Cartagena?”

“Yes. That is, I’d think so. Why didn’t you and Mr. Wallace find out while you were there?”

“Upon my word, I never thought of it,” confessed the naturalist sheepishly. “And I’m sure Bob didn’t. But we could easily have inquired. After seeing the city, I’m inclined to think the tank can be repaired there.”

They found a little later that Mr. Wallace was right. At the first garage they entered, they were informed that the tank could be repaired.

It was necessary, however, for the garage man to take his welding outfit over to the monoplane, which was in a field quite a distance away. For this he explained he would be compelled to make an additional charge, but the others, knowing there was no other way out, did not object.

When the tank was mended and had cooled an hour or so, it was filled to capacity with gasoline. The spare was also filled, and then the explorers were ready to resume their journey.

A little crowd of people had assembled to see the monoplane off. They waved a friendly farewell as it soared high into the sky.

“Now I wonder if we’ll have any more trouble,” mused Bob. “Or will we have good luck and get to the Andes without much delay?”

Across jungle, plains, and hills they flew for well over an hour. Then they caught sight of something in the distance that thrilled them with delight.

“The Andes!” cried Joe joyfully. “At last we’ve seen the Andes Mountains!”

“I believe you’re right,” affirmed Mr. Wallace, straining his eyes to make out more clearly the series of distant bumps that were mountains.

As the explorers flew nearer, they could easily observe the high peaks and narrow valleys. At one time they flew directly over a short range of exceedingly lofty mountains.

The monoplane passed farther, and the towering slopes of the Andes became more prominent. They looked dark and forbidding, yet beautiful and romantic.

“It’s going to be dark before long,” said Karl, breaking the fascinating silence. “And as it isn’t wise to keep going over unknown territory, I’m going to land—if I can find a place.”

Picking out a level spot was very difficult, but finally Karl caught sight of a flat plateau stretching several hundred yards ahead. He brought the machine down as best he could, taking into consideration the difficulty of landing at high altitudes.

They did not pitch the tent that night, but curled up inside the cabin, too tired to use much more energy. By doing this they could lock the doors and spend the night in comparative safety. Otherwise, it would have been necessary to set a guard.

A heavy slumber overtook them and held them firmly until late next morning.

“Now to head for Ecuador,” said Joe, becoming impatient. “How long will it take us—to get to Quito, I mean?” he asked Karl.

“Let’s see. We’ve been about an hour out of Cartagena.” Karl pondered for a minute. “There’ll be about six more hours of air traveling before we get there. That is, if nothing happens.”

But nothing hindered their flight, and after a thrilling ride over fascinating country the explorers came to Quito, at the very rim of the lofty peaks. Karl finally was able to bring the airplane safely down at the edge of the city. He switched off the engine, and, with the others, turned to glimpse the surrounding mountains.

On all sides were the magnificent heights of the mighty Andes, reaching thousands of feet above the city. Quito itself was built in a wide valley, nearly eleven thousand feet above sea level.

All during the last hour, as they had soared steadily upward, Joe had had a strange feeling of nausea, which grew still worse after they had landed at Quito. Now, when they were about to make their way into the city, Joe slumped down on the ground beside the monoplane.

“I’m sick!” he moaned helplessly. “Guess I can’t go with you now.”

---

“SICK?” cried Bob anxiously. “What seems to be the trouble?” He and Mr. Holton had moved over to Joe.

“Got a terrible headache. Feel bad all over. My—my stomach doesn’t seem right.”

Almost at once the two naturalists grasped the meaning of Joe’s misfortune.

“There’s no doubt about it,” began Mr. Wallace, who was himself becoming pale. “You have mountain sickness, or soroche, as it’s called. I think I have a touch of it myself.”

“What causes it?” queried Bob.

“The high altitude,” Mr. Holton answered. “You see, when one makes a sudden change to nearly eleven thousand feet, it is a great strain on him. Usually, though, it doesn’t show up until reaching a much higher altitude than this. I’m surprised that Joe has it so soon.”

Joe did not become worse, but grew no better. One thing was apparent: until he would show improvement, he could not continue the journey.

Mr. Holton and Bob helped him into the cabin of the airplane, where an improvised bed was made.

“If it’s all right, I think I’ll stay with him,” announced Mr. Wallace. “I’m not feeling any too well myself, and then, too, Joe ought to have someone here with him.”

“All right,” said Karl. “Meanwhile the rest of us will go on into the city and have some gasoline sent out to the ’plane.”

In Quito the others found a filling station, the operator of which agreed to send out a truck to the monoplane to fill the tanks.

Back at the field they found that Joe had greatly improved and was anxious to fly on to Lima. It was evident that he had had only a slight attack.

In a short time the gasoline truck arrived, the tanks were replenished, and the explorers again climbed into the monoplane.

The journey to Lima promised to be more dangerous, as there were hazardous stretches of country to be left behind. But all knew that Karl was a skillful pilot. If he had not been he could not have brought them safely out of the terrible storm that they had encountered over the Caribbean.

Mountains, valleys, towns, then more mountains were spread before them as they flew on their way to the “City of the Kings.” The rugged Andes were more impressive than Bob and Joe had imagined.

At last they caught sight of Lima in the distance and before long were hovering over it.

Karl singled out Faucett’s Field and brought the monoplane down at high speed in order to avert a catastrophe. Well he knew that landing at such an altitude would present a difficulty, even at best.

“Can hardly feel the wheels touch the ground,” remarked Bob. “Wonder how Karl knows he’s made a landing?”

They were rolling swiftly over the smooth ground when suddenly Mr. Holton cried out in fright and pointed ahead at another airplane, which was landing directly in their path.

“Look out!” he warned Karl, speaking hoarsely through the transmitter.

Karl Sutman had already seen the danger and was cutting the monoplane to one side as best he could.

He was too late, however. The other airplane came on at sickening speed, heading directly at the explorers. The wings of the two crafts touched, and the monoplane sent the other machine, which was much lighter, spinning around dangerously.

Its lower wing scraped the ground, and a support was broken. A moment later it came to a stop, leaning on its side.

Meanwhile, Karl’s monoplane had continued farther, gradually losing speed until it came to a standstill several hundred feet away from the other airplane.

“A narrow escape!” breathed Joe, as he opened the door of the cabin and stepped out. “A little more and we would have been goners.”

“That crazy guy ought to have his face smashed!” snarled Karl, directing his glance at the distant airplane. “He broke one of the prime rules of flying: Never land when there is another ’plane on the field.”

“Here he comes now,” observed Bob. “Wonder what’s on his mind?”

They soon found out. The other aviator was a native Peruvian and could not speak English, but he addressed them angrily in the native language.

Karl stepped boldly up to the man. His fist shot out and caught the native squarely between the eyes.

The man reeled and then lost his balance, falling heavily to the ground.

At that moment two men from the airdrome came running out and demanded an explanation of what had happened.

Briefly Mr. Holton told them, stressing the fact that the aviator had not waited to land.

“He ought to have his pilot’s license taken away from him,” growled Karl Sutman, when the naturalist had concluded.

The men from the airdrome were greatly angered at the strange aviator for not being cautious in landing. They addressed him in no gentle terms as he lay on the ground.

Karl’s monoplane had been only slightly injured in the accident, but it was enough to require an hour of patient labor to make the repair.

The possibility of the other aviator doing damage to Karl’s machine prompted the tall young man to ask that it be kept under watch near the airdrome.

“Now suppose we walk on into Lima,” suggested Mr. Holton, after the ’plane had been rolled over to a safe place.

At the edge of the field was a wide street that led directly into the city. This the travelers followed and before very long came to the business district. In front of the huge cathedral they stopped to view the crowds through the cluster of palm trees that was before them.

“Quite a bit of life here,” observed Bob, as his eyes followed the busy swarm of people. “Lima must be a place of considerable importance.”

“It is,” said Mr. Holton. “It’s the capital of Peru.”

In the distance, beyond the plaza, a line of lofty mountains was plainly visible in the thin air. No doubt they were many miles away.

The explorers sat down idly on the wide steps of the cathedral.

“Now,” began Mr. Wallace, “we should make plans for the next two weeks. Mr. Lewis, we know, will arrive in Mollendo in about that time. What do you suggest doing—stay in the vicinity of Lima and take in the sights here, or fly on to Cuzco and the heart of Inca land?”

“I’d rather stay where we are for a while,” spoke up Karl. “There’s so much to see here that it will be worth it to spend a good bit of time in this section.”

“That goes for me, too,” came from Joe. “We’ll go to Cuzco later anyway, so why not see what we can around Lima?”

As everyone was in favor of doing this, they agreed to find a hotel and engage rooms.

“If I’m not mistaken, we won’t regret staying in this region,” said Bob Holton.

And they did not. During the next week and a half they spent their time taking in the sights of Lima and the rugged country surrounding it. They visited the botanical gardens, the various plazas, public buildings, streets, and the national museum. They toured the fascinating country about the city, seeing the ancient Inca highway, the mines of Morococha, the lifeless native huts that were everywhere, the marvelously engineered railroads, and the interesting city of Callao, located near by.

At the end of the time that they could spend here, the explorers were well pleased with the eventful days that had passed.

“Now to head for Mollendo,” said Mr. Holton, as one morning he arose early to prepare his possessions for the trip. “We’ve only got about a day before Mr. Lewis’s steamer arrives from the United States, and we must use the time to best advantage.”

The others were ready and climbed into the airplane for the long journey.

Mollendo, the adventurers found after the interesting flight, was much like other cities they had visited. It possessed a very interesting dock, however, which held the boys’ attention for many minutes.

The following day, when it became time for the steamship to arrive, they were on hand to meet the naturalist and the others.

“It’s coming!” cried Joe, pointing excitedly toward the horizon. “And will I be glad to see Dad!”

“I guess we all will,” said Mr. Wallace.

The vessel steamed closer and headed for the port. As it came toward them, the explorers could easily make out someone on the deck whom they recognized. It was Mr. Lewis.

---

AS the ship moved slowly into port, Mr. Lewis, standing anxiously on the deck, caught sight of his friends and waved wildly. Obviously he was exceedingly glad to see them again.

Others of the expedition who recognized Mr. Holton or the boys also waved a friendly greeting, which was returned by those on shore.

When the boat had come to a standstill, a huge crane swung out and up to the deck. At the end, attached by a massive hook, was a chair. Into this the boat’s passengers were to sit and be hoisted down to the dock.

“Funny way of unloading passengers,” laughed Bob, as he watched a woman rather nervously sit down in the chair.

“No other way, I guess,” came from Mr. Wallace. “The surf billows roll too high for the conventional method.”

The onlookers watched closely as the chair was raised off the deck and suspended over to the shore.

The woman who was carried in this manner laughed as she left the chair and turned to see the motion repeated. From the look on her face, it had been an exciting experience.

“Here comes Dad!” observed Joe happily. “Wonder how he’ll like it?”

Mr. Lewis had seated himself in the chair and was being carried high in the air to the dock.

When he set foot on the ground, he rushed toward the others, on his face a look of intense joy.

Words fail to describe the meeting that followed. Mr. Lewis was literally mauled by his son and friends, who were overjoyed to have him again with them. Especially was Joe happy.

“I worried from the time you left Washington,” the naturalist told them, throwing an arm over Joe’s shoulder. “The more I thought about that airplane trip the more anxious I became. You didn’t have any trouble, did you?”

“It’s according to what you call trouble,” laughed Bob. “If you mean accidents, we didn’t have any. But if you mean just common bad luck, we had plenty.”

“Could have been worse, though,” his father reminded him. “And let me tell you that Karl is an excellent pilot. If he weren’t, we probably wouldn’t be here now.”

“As if I didn’t know it,” smiled Mr. Lewis, glancing at the blushing aviator. “If anyone else had offered to take you to Peru, I wouldn’t have thought much of the idea. Karl Sutman, though——”

At this moment a group of men came up, to be recognized by Mr. Lewis and Mr. Holton.

The youths, Mr. Wallace, and Karl were introduced to them as members of the archæological and geological divisions of the expedition. Dr. Rust, Professors Allan and Kelley, and Mr. Dunn, as their names were, had come to this region to search for additional Inca ruins and to study the land in the mountain section.

Two other men completed the personnel of the expedition. They were Mr. Buenagel, assistant, and Dr. Brown, physician, both of whom had been on numerous expeditions with the others. They now came up and received the same hearty welcome.

“Now that we’re all together,” began Dr. Rust, “we want to decide where we’ll make our headquarters. Is everyone in favor of having our base in or near Cuzco?”

“I should say yes,” came from Professor Kelley. “Cuzco, after all, is a very strategic point, and is quite easily accessible from all parts of this section. So why not locate there?”

As everyone agreed, the question was settled. Now came the problem of transporting the expedition’s supplies, of which there were many.

Karl generously offered the services of the monoplane in getting the trunks and bags over to Cuzco. He explained that he would be glad to do this for them, even though it might be necessary to make two or three trips.

But Dr. Rust, leader of the expedition, stoutly refused.

“We don’t wish to put you to that trouble,” he said. “As long as there is a railroad running up to Cuzco, we’ll make use of it and have our stuff shipped, even though it may take a few days longer.”

Karl wondered afterwards if the scientist secretly feared an accident. The tall young man remarked to Bob and Joe several days later that perhaps Dr. Rust did not wish to take a chance on the monoplane crashing with the expedition’s supplies on board.

As had been suggested, the supplies, including those of Mr. Holton and Mr. Lewis, were placed on board the first train that left for Cuzco. The boxes and trunks would not reach their destination until several days later, however, since it was necessary for them to be changed around several times.

Except for the three naturalists, the scientists boarded the same train for Cuzco. Mr. Wallace and the youths’ fathers were to accompany Karl and Bob and Joe in the monoplane. With Mr. Lewis in the cabin, there would be an added load, but Karl told them it would not be dangerous.

“Just have to watch the take-offs and the landings more closely,” the aviator explained. “Outside of that, we’ll never know that another person is inside, as far as the ride goes.”

“Won’t ride any easier?” queried Joe, trying to appear innocent.

“Quit your kidding!” snapped Karl with a laugh. “This bus isn’t an automobile.”

“But a bus is an automobile,” said Joe persistently.

He dodged a pass that Karl swung at him. Then, seriously, he turned to the others, who were busy attending to minor tasks about the airplane.

“Everything’s ready,” announced Mr. Wallace, stepping inside the cabin. “Suppose we get started at once, so as to get there and look around some before the others arrive by train.”

Karl was willing. He climbed into the cockpit and started the engine. Mr. Holton, the last to enter the cabin, closed the door tightly just as the monoplane began rolling over the field.

“We’re off for Inca land!” shouted Bob excitedly, raising a motion-picture camera to his shoulder. “And won’t we have fun!”

“We’ll also have a little work,” said his father quietly. “If we get enough specimens from this region to satisfy the museum heads we’ll have to go some.”

Flying over this interesting land was exciting to the youths, who viewed the sights curiously. Before long they could make out the town of Arequipa away over to their right, and just behind it, El Misti volcano, whose sides sloped up to a point.

Karl guided the ’plane as near the ground as possible, knowing that he and his friends could not stand the rare air of several thousand feet higher without the use of oxygen. A few tanks of this valuable gas were now on the train en route to Cuzco. Karl had not thought it necessary to use them in the ’plane so soon.

At the speed they traveled, it did not take them long to sight Cuzco in the distance. Several miles away they could also see the town of Anta, which was a mere village compared to its neighbor city.

When they came nearer, Karl flew straight for the central plaza, so as to get a fine view of all the buildings and places of importance.

“Look at the people swarming to see us,” said Joe. “I guess it isn’t often that an airplane comes here.”

At about three hundred feet they soared leisurely over the central plaza, where natives were gathering rapidly. Directly below them was the huge cathedral, which, as far as they could see, was the most imposing building in the city. All about were low structures, with an occasional higher building dotting the landscape.

It was a wonderful view. Even from that low altitude, the explorers could easily make out the surrounding mountains, on many of which were Inca ruins, including the “staircase farms.”

Joe considered it a wonderful opportunity to take several hundred feet of motion pictures. He pointed the camera first at the city below them, then at the near-by mountains, turning the crank continuously.

When he had flown a few times around the town, Karl picked out a level stretch to the east and began the dangerous task of landing. Well he knew at that altitude it would be easy to crash.

The monoplane headed downward at high speed, the wheels touched the ground, bumped back into the air, touched the ground again. The machine rolled ahead at fifty miles an hour, forty, thirty, and finally came to a stop dangerously near a large pile of stones.

“All out,” called Karl, when he had switched off the motor. “We’re here. And we came down without a smash-up.”

Directly across the river Almodena the adventurers could see Cuzco, looking strangely quaint in its pocket in the mountains.

“Here come more natives,” observed Mr. Holton, as a horde of twenty or thirty men, women, and children rushed toward the Americans.

As they came nearer, they uttered something that none of the newcomers understood.

“They’re speaking in Quichua—that’s the native tongue in this part of Peru,” explained Mr. Lewis. “It’s the same language that was used by the ancient Incas.”

Although the natives scrutinized the airplane carefully, they were not bothersome, staring rather in awe at the great “bird” that had come mysteriously to their city.

Karl thought it best to have the craft guarded against possible marauders. But how he could secure a guard was a problem, since none of the Indians could understand English or Spanish. And the aviator knew not one word of Quichua.

“Suppose we take turns watching it,” suggested Mr. Holton. “I’ll take the first watch of, say, two hours. Bob, you can take the second, and so on until we can make some other arrangements.”

“And while Dad’s staying here with the ’plane,” began Bob, “I’d like to look around a bit. Anybody want to go with me?”

“Sure.” Joe was anxious to see the sights in this strange land.

“Don’t be gone long, boys,” cautioned Mr. Lewis. “We all want to be on hand when the train arrives from Mollendo.”

The chums walked south over a level plain, hoping to see something of interest before long.

They had not long to wait. In a little open grassy stretch beside a wall of rock was a herd of ten or twelve llamas, grazing peacefully. These animals were about 4 feet high, with long necks and a head like that of the camel.

“Let’s go up and see them,” said Bob, moving over to the herd.

“Better not,” warned Joe. “They might be dangerous.”

“Dangerous? Those things dangerous? Wait a minute and I’ll show you how peaceful they are.”

Bob had walked up to the foremost black animal and now began to stroke its woolly back.

Then an unexpected and unpleasant thing happened. The llama turned suddenly on Bob and spat violently in the youth’s face.

---

BOB shook his head to rid himself of the sickening saliva. He wiped his face with his handkerchief, with his hands, with anything he could find. At the same time he stepped out of reach of the treacherous animal.

When he had completed rubbing, he turned sheepishly to Joe.

“Guess I learned my lesson,” he said quietly. “But who’d ‘a’ thought it of the brutes?”

“Isn’t wise to do anything unless you know what you’re doing,” Joe reminded him.

“I’ve a notion to go over and wring its neck!” snorted Bob, glancing at the llama, which had resumed its grazing as if nothing had happened.

“Better not,” Joe warned him. “You might not be able to do it. And the Indian that owns them might come out.”

“Let him come!” Bob was confident that he could manage both the llama and the Indian.

He decided to let the matter drop, however, and continue the walk about the plateau.

As the youths hiked farther, they passed the grassy region and came to a higher slope that was dotted with occasional patches of cacti, thorn bushes, and stunted trees. The Australian eucalyptus, a small tree, was abundant.

“Can’t raise anything here,” remarked Bob. “Almost as bad as it is on the Sahara Desert.”

The chums made a wide circuit about Cuzco, coming in sight of the monoplane from the opposite side.

“You’re just in time to stand guard,” Mr. Holton told Bob. “And while you’re doing that, the rest of us will look around a bit. We’ve all been busy studying maps of the Andes.”

The adventurers took turns watching the airplane and seeing the country all during the remainder of that day. If it were able to follow schedule, the train from Mollendo, bringing the others of the expedition, would arrive the next afternoon.

At that time all the air travelers but Mr. Lewis were in the railroad station waiting. Mr. Lewis had remained at the field to guard the ’plane.

“It’s coming,” said Mr. Wallace, and a minute later the train pulled up and stopped.

Dr. Rust and the other scientists stepped off, to be met by the naturalists and the youths.

“I think it might be wise,” began Mr. Holton, “to establish a temporary camp here near Cuzco, perhaps in the field by the monoplane. Is everyone with me in this?”

Professor Allan nodded.

“I am in favor of it,” he said. “Until we make further preparations for our work in the mountains it would be wise to put up our tents there.”

At the field they found Mr. Lewis waiting for them. He also agreed to follow Mr. Holton’s suggestion.

Four tents were pitched in a semicircle beside the airplane. The expedition’s supplies were placed systematically inside, and then began a discussion about the coming exploration.

“We who are after Inca ruins have decided to set off for the region near Mount Panta,” Dr. Rust said. “In our opinion, there is an opportunity to find wonderful Inca remains in this section. Most likely we will stay within twenty miles of that mountain for three or four weeks. Where we will go then we will have to decide later.”

“Now of course you archæologists want to know as nearly as possible where we naturalists will be,” began Mr. Holton. “I don’t know whether everyone will agree,” he went on, “but I know of a place that supposedly abounds with wild creatures. And I would suggest that we head for that spot.”

The others looked at him inquiringly.

“This morning while I was out scouting around I came across an American who was just returning from a hunting trip in the Andes,” Mr. Holton resumed. “He informed me that the valley of the Comberciato is teeming with wild game. According to his estimate, that’s about a hundred miles from here, northwest. It——”

“I’ve heard of it, too,” cut in Mr. Wallace, his face beaming with scientific enthusiasm. “Why not go there? We’ll probably find it worth our while.”

“I’m willing,” came from Joe’s father.

“Then let’s call it settled,” Mr. Holton said. “We’ll start out as soon as possible.”

“Here’s where Mr. Sutman and his airplane come in,” remarked Professor Allan. “By the use of the ’plane, we can keep informed as to the whereabouts of the other division of the expedition. It will prove a valuable asset to our equipment.”

Bob and Joe and Mr. Dunn took it on themselves to go back to the railroad station and have the many boxes of food and supplies removed to the camp. The scientists had purposely left them in charge of the agent until after deciding the course of the expedition and had carried only the lighter bags and cases to the camp.

The railroad agent, when asked of a means of transporting the boxes, pointed outside to a large cart drawn by a mule. Walking lazily at the side was an Indian.

“He will do it for you,” the railroad man said in poor Spanish.

Then, knowing that the Americans could not speak the Quichua language, the agent called to the native and asked if he would be willing to take the boxes.

The Indian merely nodded and went into the building after the first load. In all, there were about seventy-five cases, and he knew it would be necessary to make several trips.

“That mule doesn’t look any too willing to pull the load,” observed Joe with a laugh. “Be funny if he’d stop still when only about halfway there.”

When the cart was loaded with about fifteen or twenty of the boxes, the Indian called for the animal to pull ahead. But the stubborn mule refused to budge.

“Now what will he do?” mused Joe, looking at the impatient Indian.

He soon saw. The native removed five boxes and carried them back into the station. Then, with the cart lighter, he again attempted to make the mule move ahead.

But apparently it was still too much of a load, at least for comfort.

“That crazy donkey just doesn’t want to go, that’s all.” Mr. Dunn had been taking in the incident with a great deal of interest.

The Indian was becoming impatient. He had apparently removed all he was going to from the cart and intended to resort to force.

Walking to one side, he pushed with all his strength on the balky animal, at the same time saying something in Quichua that the whites guessed was not pleasant.

Slowly, very slowly, the mule struggled forward, snorting as if in rage. Gradually he quickened his pace, but never exceeded a walk.

“At this rate it’ll take us the rest of the afternoon to get everything in camp,” muttered Bob, amused and yet angered at the stubborn beast.

The youth guessed fairly right. The sun was almost ready to sink below the horizon when the last box was unloaded from the cart, after five trips had been made to carry all of the supplies.

“Too late to do anything tonight,” said Mr. Lewis, as the Indian, mule, and cart disappeared over the plateau. “I suppose we’d better take it easy, anyway. We’ll have some busy days ahead of us.”

Early the next morning the explorers were up preparing for the mountain journey.

“The first thing now is to get mules,” said Mr. Wallace. “And,” he added with twinkling eyes, “they’ll have to be faster than the one that carried our stuff last night.”

“You forgot.” Dr. Brown, the physician, was moving up to Mr. Wallace. “The first thing isn’t to get mules,” the doctor continued with a smile. “Medical attention always comes before anything else.”

“That means a physical examination?” asked Bob.

“Yes. And it also means vaccination against smallpox and typhoid fever. Those two diseases are very common in this part of Peru.”

Dr. Brown had attended to everyone but the youths and Mr. Wallace. But it did not take long to finish with them.

“Now as I was saying,” began Mr. Wallace, “the next thing is to get mules. And I know where we can find them. I inquired yesterday and found that a wealthy Peruvian who lives at the edge of Cuzco can let us have as many as we need. He will also see that we get native guides.”

“Don’t forget that we need about twenty-five mules—for both parties of the expedition,” Professor Allan reminded him.

“I haven’t,” the naturalist returned. “We can get as many as we need. Suppose we do it now.”

Mr. Wallace, Dr. Rust, and Professor Kelley set out at once to get the pack animals.

Meanwhile, Bob and Joe took movie cameras and walked leisurely up the hillside, intending to photograph anything that would come before them.

The boys had not gone far when they came upon a large group of Indian men, dressed in short, coarse trousers, hand-woven shirts, and brightly colored blankets. On their heads were the flat “pancake” hats which are common in this region.

“Here’s a good chance to take movies,” said Joe happily. He had brought the camera to his shoulder and pointed it toward the Indians, turning the crank steadily.

Suddenly the natives rushed angrily at the youths and made a grab at the motion-picture cameras.

---

“LET go!” cried Bob, in his excitement forgetting that the Indians could not understand English.

The group had completely surrounded the youths, and one man was holding tightly to Bob’s camera.

The two chums knew that they had little chance against so many. But they fought doggedly to save the moving-picture machines, which were the only two they had.

With one supreme effort, Bob pushed the Indian nearest him to the ground and turned to find an opening in the crowd of natives.

But they were all about him, pushing and grabbing and striking to the best of their ability. It was plain that they were determined to take possession of the small boxes that the whites carried.

If it had not been for the necessity of holding onto the cameras, Bob and Joe could have put up a good fight, and perhaps driven the Indians away. But as it was they found themselves at a sore disadvantage.

“Help!” cried Joe, raising his voice to a shout. “Help! Help!”

Several seconds later a figure showed itself at the brink of the hill and came toward the fighting group.

“It’s Dad!” Joe cried happily. “Now there’ll be a fight!”

Mr. Lewis was soon joined by Mr. Holton and Karl Sutman. Like a flash the three grasped the meaning of the scuffle and rushed to the aid of the chums.

They dived headlong into the furious mob, using their fists to great advantage. One big fellow Mr. Lewis knocked flat on his back in a daze.

“Here, take my camera,” directed Bob, speaking to Karl. “Run as fast as you can back to camp. I want to take a lick at some of these beggars.”

Karl did as asked and dashed out of the mob for the tents. The last Bob saw of him he was rounding a bend and heading toward the monoplane.

Then Bob faced the man who had grabbed his camera.

“Take that!” the youth snarled, sending the Indian crashing to the ground.

The other natives, seeing that they were unable to hold their own against these whites, took to their heels and disappeared in the distance, kicking up a cloud of dust behind them.

“Well, we licked them.” Mr. Lewis was panting for breath. His face was red from fatigue, his clothes torn and wrinkled.

And the others were no better off. They had put up a game fight, determined to drive away their enemies.

“What was their motive for attacking you?” inquired Mr. Holton, wiping his face with his handkerchief.

“Beyond us,” Joe answered him. “We just looked at them and pointed our cameras at them——”

“Oh.” Mr. Holton seemed to understand everything. “That’s all you did, huh? Well, you did enough to excite their anger. Those natives are decidedly against having their pictures taken. They believe that any evil which might befall their pictures will come upon them later.”

“So that was it?” Bob laughed. “Well, we’ll know enough not to try the same thing again. Anyway, we got several feet of film exposed, and that’s better than nothing.”

The adventurers made their way down the hill, to be met by Karl and the others of the expedition, who had come to learn of their friends’ misfortune.

“Quite an encounter,” commented Mr. Dunn, when he was told the details. “These Indians are bad characters when their anger is aroused.”

Back at the camp, the explorers got everything in readiness for the expedition to depart as soon as Mr. Wallace, Dr. Rust, and Professor Kelley returned with the mules and guides.

It was nearly noon when Bob caught sight of a long line of mules heading toward the camp. They were coming slowly and leisurely, but always closer. Near the rear were the three explorers and two natives, who had been driving the animals.

“I see you met with success,” said Mr. Buenagel, addressing Mr. Wallace.

“Success is right!” the naturalist was beaming all over. “Don Chusmena here”—indicating a small Peruvian who had been conversing with several natives—“has generously offered to let us use twenty of his mules. They are all fine specimens, worthy of making the mountain trip. And the price is right.”

The mules were driven up to the camp and herded together in a group.

Mr. Wallace introduced Don Chusmena to the others. The Peruvian in turn acquainted the Americans with the Indians who were to act as guides for the expedition. He assured them that the natives knew every foot of ground in the Andes country. One Indian was to lead Dr. Rust and the other scientists who were to search for Inca ruins. The other native would guide Mr. Lewis and any others that might be in the party of naturalists.

Both Bob and Joe had decided to stay with the expedition and not fly in the monoplane with Karl Sutman. Mr. Holton, however, intended to accompany the aviator and Dr. Brown, the expedition’s physician. Karl and the two men were to fly on ahead and look for Inca ruins from the air, keeping in touch with the others. It was intended that Karl head for the valley of the Comberciato, where he and Mr. Holton and the physician would await the others of the naturalist party.

“That leaves you and Mr. Wallace and Dad and I together,” remarked Joe. “I’m sorry your father isn’t going with us.”

Bob nodded.

“He’ll meet us at the Comberciato River, though,” the youth said.

“But that won’t be until two weeks from now, at least.” Joe would have been better satisfied if Mr. Holton had intended to go on foot instead of in the airplane.

Mr. Lewis and Mr. Wallace desired to get their division of the expedition started as soon as possible. But since it was so late they thought it best to wait until the next morning.

“That’ll give us time to look around some more,” said Joe, picking up a motion-picture camera. “Come on, Bob. There’s a lot to be seen around Cuzco.”

“Be careful boys,” warned Mr. Holton. “Don’t try to photograph any more Indians, or you may get into a bigger scrape than the one this morning.”

“Leave it to us,” laughed Joe. “We’ll be all right.”

The youths headed west toward the river Almodena. They resolved to cross it and proceed northward to the Fortress of Sacsahuaman and other Inca ruins.

From the river there was a narrow road that led up the plateau to the high hill that overlooked the city. As this hill stood between the boys and the ruins of the fort, which were located high upon another cliff, they found it almost necessary to climb to the top and then down the other side.

“Now for the ruins,” said Bob eagerly, pointing to the top of the low mountain that was before them.

The youths had begun the difficult climb to the summit and had rounded a turn in the rocks when they caught sight of an old man climbing slowly up the dangerous ridge.

“Look!” cried Joe in terror. “He’s falling!”

The old man’s foot had slipped, and he was trying as best he could to balance himself on a narrow ledge.

His efforts were in vain. The next moment he began to plunge helplessly downward.

With the quickness of a cat, Bob stepped forward and, bracing himself as best he could, he threw himself against the man. The impact of Bob’s heavy body stopped the man’s fall and sent him against the side of the cliff. It bruised his face and shoulders, but he was safe.

After a few moments of resting, the old man looked up, wild-eyed and white with fear. There was an expression of intense gratitude on his wrinkled face as it was turned toward Bob.

“You saved my life!” he cried in excellent English, gazing fearfully below. “And I want to reward you. I want to tell you of some Inca secrets—secrets of the Andes!”

---

AT once Bob and Joe were breathless with interest. They had often heard of Inca secrets but had thought them nothing more than myths. Now, as this strange old man stood before them, the youths wondered if there might have been some truth in the fantastic tales told of Inca mysteries.

The old man hesitated for several minutes, staring off into space. Then, when the youths were becoming impatient with the long silence, he continued, speaking in a low voice.

“Far, far away, in the heart of a huge mountain, is a narrow tunnel that leads to a large cavern of Inca secrets.” Again the stranger hesitated, looking below at Cuzco.

“Why doesn’t he hurry?” thought Joe, almost saying the words aloud.

Finally the old man continued.

“This cave is so large that it occupies the entire mountain,” he went on. “It is lighted with a strange brilliance, that comes mysteriously from the outside. But ah! The Incas were marvelous inventors. They could do many things that we Americans cannot do.”

“Then you are an American?” inquired Bob quickly.

The old man nodded.

“I spent my early years in the United States,” he explained. “Graduated from college and set out to be a scientist. Then I became interested in Inca ruins and came here to look for them. My entire lifetime I have spent in these mountains, looking for ruins and treasure.”

“Treasure?” cried Joe. “Is there treasure here?”

“Undoubtedly there is,” was the answer. “In fact I believe I have found some.”

The young men were all excitement.

“Tell us about it!” begged Joe.

“I am not certain that I have found any,” the stranger said. “But I came across a sort of bin that is covered with a heavy stone block. Alone I am not able to lift it off. I firmly believe that in the bin is something valuable. This is in that cave I told you about.” He stopped and glanced about; then, satisfied that no one else was near, he continued: “It is a long, hard journey to this wonderful place. There is a secret trail, that is known only to myself. And to add to that, there is a single entrance to the cave. It cannot be opened until you press a hidden button.”

He stopped a moment and gazed thoughtfully at the young men.

“You saved my life,” he went on, looking at Bob gratefully. “For this I will gladly give you half of any treasure in the bin, if we can find any. Will you make the trip with me?”

For a few moments the youths said nothing. They wondered if there was really any treasure in the bin. And they wondered, too, if it might be possible to locate still more in the near-by mountains.

“I am willing to go,” said Bob at last. “It won’t put us out any, I’m sure. I think we can arrange it some way. Maybe Dad——”

He got no further, for at that moment the old man raised a hand for silence.

“Of course your dad is all right,” he said conclusively. “But I do not wish to take anyone but you and your friend here with me. Even your father might without thinking tell someone about this secret, and then we would lose everything. And I want no one else to know.”

“Then,” began Bob, “you want only Joe Lewis here and myself—my name is Bob Holton—to go with you?”

“You are right,” came the reply. “And my name is Rander—Doctor Rander. I would be much better satisfied if only we three went.”

“I think it can be arranged,” Bob told him. “What direction do we have to go?”

“East. Almost straight east from Cuzco. But of course there are many roundabout paths that we must follow, and much of the way is over no trail at all.”

“We’ll let you know a little later, if that is all right,” said Bob. “Where can we get in touch with you?”

Dr. Rander explained that he was staying in a little adobe hut at the other edge of Cuzco and that he had a sufficient number of mules to carry the provisions needed.

“How soon do you want to start?” inquired Joe, who was anxious to make the trip.

“I am ready any time,” the old man said. “If you wish, we will start tomorrow.”

Bob explained that they would talk it over with their fathers and call on their friends that night. With this, the youths headed back to camp, not desiring to lose more time even in seeing the ruins at the top of the hill.

“What do you think of it?” asked Bob a little later, as he and his friend came in sight of the monoplane.

“I think a lot of it,” Joe answered. “Why, it will be wonderful!”

“Don’t be too sure that we can go,” Bob reminded him. “It all depends on what our dads think. If they’re afraid to let us leave the expedition and start out with this Dr. Rander, why, I suppose that will end it all. And the old man won’t let anyone else go with us.”

“Funny he’d tell us about that secret, isn’t it? If he had kept still, he’d have had all the treasure for himself. But then, I suppose he was so glad you saved his life that he was more than willing to let you in on it. Then, too, he’s not sure of finding it.”

At the camp, the boys found their fathers and others awaiting them.

“What do you think of the ruins?” asked Mr. Holton, as the chums came up.

“We don’t know much about them,” returned Joe. “But there’s something else we want to tell you.”

While the men listened, Joe told of seeing the old man climbing up the steep hill and of Bob’s saving his life when he fell. He told of the secret treasure that the stranger said was in the Andes, and of the old man’s desire for the two youths to accompany him in the mountains. He finished by saying that he believed it might be worth while to go.

“Perhaps you’re right,” came from Mr. Holton. “It might pay you to go with him. Do you think he can be trusted?” Mr. Holton had great faith in the judgment of his son and Joe.

“Don’t know why not,” said Bob. “He seemed so glad that he had not fallen down the cliff that he was happy to tell us about the treasure.”

“There isn’t a chance of his being crazy, is there?” asked Karl Sutman, who was also listening to the conversation.

“Oh, of course there’s a chance,” replied Bob, “but I’d be willing to bet anything that he isn’t.”

“We can go with him, can’t we?” queried Joe, glancing especially at his father. “We may find treasure, after all.”

“I see no reason why you shouldn’t,” came from Mr. Lewis. “Of course you’ll be careful. And there’s very little danger of getting lost, with all the native huts scattered about. What do you think, Howard?”

“Like you,” Mr. Holton replied. “After all, Bob and Joe are able to take care of themselves. If Karl will stay in the vicinity of Cuzco until they get back, it will ease matters some. Or, if the boys will be gone too long, Karl can come on with the rest of the expedition to the valley of the Comberciato, and then return later to pick up Bob and Joe in Cuzco.”

“I’ll be glad to do it,” Karl Sutman said, and so the matter remained settled.

That evening Bob and Joe went to Dr. Rander’s hut at the edge of Cuzco. The old man seemed glad to see them, offering them the best chairs he had.

“Now about the secrets,” he began, after he had closed the door and made sure that no one was near. “First of all, we must keep it strictly to ourselves. If, while on our way, anyone should ask why we are going into the mountains, we must not tell them.”

“For one thing, we’re going to take movies of the country,” said Joe, and then explained this in full to the old man.

The youths spent all evening at the old man’s hut. When at last they were ready to leave, they had agreed on one thing: They were to start early the next morning.

As they walked silently back to the camp, gazing up at the starlit sky, Bob and Joe wondered what would be their adventures for the next few weeks. Would they actually come into possession of valuable treasure?

---

EARLY the next morning the youths were up getting ready for the long journey into the unknown. They had all their possessions packed when Dr. Rander came with mules and provisions.

He was introduced by Bob and Joe to the other members of the expedition, who, particularly Mr. Holton and Mr. Lewis, recognized him as a capable explorer.

The youths made arrangements for Karl Sutman to meet them in a town called Pasaje, at the end of a sufficient time. The aviator was to have his monoplane ready to take the youths to the locality occupied by other divisions of the expedition.

“Now do be careful and don’t take any chances,” warned Mr. Holton, after additional boxes of food had been strapped on the backs of other mules. “Remember, slow traveling with safety is far better than rapid going with danger.”

“We’ll be all right,” Joe assured him, as the mules were being placed in line. “And Karl will fly us to your locality in due time. Don’t forget that you are to be careful too.”

With fond farewells, Bob and Joe and the old man drove the mules toward the rim of mountains that skirted the eastern horizon. They rounded a high hill and lost sight of their relatives and friends.

For some time the youths were silent with their thoughts. Who knew whether they would ever see those dear ones again? Even at best, there were untold hardships and dangers in the mountains that lay before them. Would they be able to meet any crisis?

It was some time before the boys resumed their natural peace of mind. But when they did, they were eager to take in all the sights of this wonderland.

There was a wide trail that led eastward from Cuzco. Over this the pack train went at a slow but steady gait that promised to eat up the miles sooner than it might be thought possible.

“Wonder if we’ll see any big game?” remarked Bob, as he and Joe walked near the rear of the pack train. “I’d like especially to bag one of those white condors Dad was talking about. You think there are any?”

“Possibly,” replied Joe. “But if there are, it isn’t likely that we’ll see one.”

The three adventurers followed a well-beaten path to the town of Puquiura, which they found nothing more than a group of native mud huts.

“Not much life here,” observed Joe, as the caravan of pack animals passed on through the village.

“I suppose this is typical of all the towns in these mountains,” came from Bob. “Just a bunch of dirty mud dwellings.”

Led by Dr. Rander, the Americans wound around a narrow trail that reached steadily upward. They were making fairly good time, and if nothing prevented, they expected to arrive at a much larger town before noon.

“I think I’ll try riding my mule,” announced Bob, who, along with his friends, had been walking beside the mounts.

“Better watch out,” cautioned Joe. “Those little animals are treacherous sometimes.”

Bob called to Dr. Rander to wait for him. Then, pulling his mount out of the line, he placed his foot in the stirrup and threw his leg across the sturdy little mule’s back.

But just then something happened. The animal wheeled about, and, throwing its hind feet high in the air, it leaped forward with a snort of resentment.

“Help!” cried the amused and yet worried Bob.

“What do you want me to do?” inquired Joe, taking in the scene with interest.

“Grab hold of his tail! Do anything!” Despite his serious predicament, Bob could not help laughing, although he was angered.

“Get hold of his tail, huh? Not much.” Joe intended to derive as much amusement as possible from his friend’s plight.

All joking was cast aside a moment later when, at an unexpected moment, the mule gave a quick turn to the left and threw Bob to the ground. The youth caught the fall with his arm, and so escaped injury, but his anger was as strong as ever.

“I’ll fix you, you——”

Bob did not finish the words, for at that moment the mule leaped forward and galloped off at a rapid pace.

“After him!” Bob cried, dashing ahead as fast as his legs would carry him.

A more amusing sight could hardly be found. Joe’s laughter mingled with the sound of rapidly moving hoofs, and even old Dr. Rander joined in the merriment.

“Think he’ll catch him?” queried Joe, as pursuer and pursued vanished behind a heavy cloud of dust.

“I believe so,” the old man returned, straining his eyes to make out the figures ahead. “The mule will soon tire of such fast running. He isn’t used to it.”

Dr. Rander was right. Five minutes later Bob appeared from around a hill leading the now calm animal. There was a smile of triumph on the youth’s face as he faced his friends.

“Now that everything has worked out all right, suppose we forget that anything happened,” grinned Bob, as he placed the mule back in the line.

“You going to try riding him again?” asked Joe with a laugh.

“Not on your life. I value my hide too much for that.”

They set forward, heading for the distant high peaks, which were always visible.

An hour of steady climbing brought them to a high plateau, which was bordered by mountains. From this elevation the explorers could command a good view of Cuzco, which seemed but a miniature city in the distance.

“I don’t feel so well,” groaned Bob, whose face was becoming pale. “I can’t get my breath without wheezing. And my stomach seems out of order.”

Dr. Rander happened to be near when Bob complained, and lost no time in attending to the youth.

“You probably have soroche, or mountain sickness,” he said, noting that Bob’s pulse was unusually rapid. “Do you think you can keep on to the next town?”

“Sorry, but I’m afraid I’ll have to lie down somewhere.” The stricken Bob was visibly becoming worse with every minute.

“Wonder if I’ll have another touch of mountain sickness?” mused Joe, as his friend stretched out on a blanket that Dr. Rander had spread on the hard ground.

There was nothing to do but wait for the youth to recover. The old man explained that often patients remained ill for several days, and that there was a possibility of Bob’s sickness being lengthy.

In view of this, they thought it best to make camp and prepare to stay as long as necessary. There was no use making arrangements to continue the journey until Bob’s condition improved.

“Here, take this pill.” Dr. Rander held a little white tablet and a cup of water. “It will make you well sooner than anything else.”

But it was not soon enough for Bob. All the remainder of that day he moaned on with a splitting headache and terrible nausea. It was worse, he said, than sea sickness, of which he had experienced a touch on his first ocean voyage.

The next morning, although still weak, Bob was greatly improved. The ill effects had gone, and once more he had an ambition again to get to the trail.

But Dr. Rander protested.

“You are not strong enough yet,” he said. “We’ll wait till noon and see if you’re improved sufficiently by that time.”

By the time the sun was directly overhead, Bob was his old natural self again. He was overly anxious to make up for lost time.

Lunch over, the explorers again took to the trail, driving the staunch little mules along at a rapid pace.

“Now lead me to those secrets of the Andes!” said Bob, as Cuzco faded from view.

At length the adventurers came to another town, which Dr. Rander called Cameras. They would much rather have encircled the settlement, but as there was no other trail, they passed on through.

“Let’s leave the mules here near the edge of town,” suggested Joe. “I’d like to go back to that little store that we just passed. Might be able to get something we can use cheap.”

“I’ll go with you,” said Bob.

Dr. Rander announced that he would stay with the mules and catch a short rest. He cautioned the boys not to stay too long.

The store that Joe referred to was nothing more than an adobe hut filled with curios of the Andes. They purchased a few articles as souvenirs and started back to the edge of town, where the old man was waiting.

Suddenly there came the sound of rough voices, and a moment later a dozen shots rent the air.

---

“WHAT’S going on?” cried Joe Lewis, as a chorus of voices mingled with the sound of rifle shots.

“Some trouble somewhere,” returned Bob. “Wonder——”

He did not finish, for at that instant there came another shot, and a bullet whizzed by his ear.

The youths lost no time in hiding behind a small mud hut, although they knew a bullet could probably penetrate it. But at least it offered temporary shelter, and that was what they wanted.

“Look!” cried Bob, gazing cautiously around the corner of the hut. “There are soldiers in uniform. What do you suppose they’re doing?”

They were soon to see.

The troops, which numbered about thirty, were firing at something that the boys could not see from their places at the side of the hut.

“I’m going to take a chance and get out in the open where I can see something,” said Joe. “Come on. If we’re careful and don’t get in the way of the shooting, we’ll be all right.”

Carefully the chums edged around the side of the dwelling and peeped out at the street. Then they drew back quickly, as a score of shots rang out.

What the youths saw was forty or fifty natives scattered out to escape the fire of the soldiers. Each held in readiness an old rifle, which he discharged at intervals.

“Must be a revolution,” observed Bob. “Perhaps those natives have offered violence to the governor of the town, and the troops have been called to settle the matter.”

Bob could not have come closer to the facts.

“The soldiers are winning,” said Joe. “They’re better trained and have more efficient guns.”

Although the troops appeared to gain the upper hand, the fighting continued with as much fury as before.

A sudden fusillade of bullets coming dangerously near Bob and Joe prompted the boys to make a dash toward the end of the town, where the mules and Dr. Rander were probably waiting.

“Let’s get out of here,” suggested Joe. “We’ll get hit if we don’t.”

“All right. Wonder if Dr. Rander is still where we left him?”

The chums were greatly surprised when, a few minutes later, they saw that the old man was not in sight. But the mules were tethered to a stout post, and this gave the boys hope.

“Chances are, he’s gone to see what the shooting’s about,” Bob said. “Wish he’d come back. He’s likely to get killed if he stays around there close.”

The youths were beginning to worry when Dr. Rander appeared up the road, glancing occasionally over his shoulder.

“Quite a commotion, wasn’t it?” he said when he had come nearer. “But the soldiers drove them away.”

“What was it, a revolution?” inquired Joe.

“Yes. An Indian told me that the people in the town were turning against their prefect. Didn’t like his rule, and wanted a change. But the soldiers soon fixed them.”

“Is the fighting over?” Bob had not heard a rifle shot for several minutes.

“Yes. The soldiers forced the citizens to throw away their weapons.”

“And that reminds me,” laughed Joe. “We’d better be getting our rifles out, because we may see some game before long. I’d like to get a shot at a condor.”

“Condors live only in high mountains,” explained Dr. Rander. “We won’t see any for many days, if at all.”

But although the adventurers did not catch a glimpse of these huge birds, they saw occasional small animals, such as rabbits and chinchillas. Once Joe took a shot at one of the latter creatures, but his aim was not steady and he missed.

At noon that day they came to a small adobe hut, from which hung a green wreath.

“What does that stand for?” asked Bob innocently. “Is somebody dead?”

For the second time since the youths had known him, old Dr. Rander burst out in laughter.

“Hardly,” he said finally. “A green wreath means that bread is for sale.”

Joe almost choked with laughter.

“That’s a good one on you,” he said to his chum. “It’s a wonder you didn’t go and gather flowers and offer them to the bereaved family.”

Bob grinned.

“You’d probably have asked where the corpse was,” he said. “Or maybe——”

“We can stop here for a meal,” Dr. Rander interrupted. “It is best to save our provisions as best we can, because later on we won’t be able to find any native huts.”

Inside the mud building, the three were waited upon by a huge Indian woman, whose hard face inspired no trust from the explorers. But they were glad when she spread before them a bountiful meal of potatoes, roast mutton, and a drink which the youths guessed was intoxicating.

“None of that brown liquid for me,” came from Bob, looking with suspicion at the huge clay cup that contained the beverage.

“Me either,” echoed Joe. “Too big of a risk.”

The old man, however, drank freely of the beverage and seemed pleased with its flavor. Whether he knew of its ingredients the chums did not know.

As soon as the meal was over, the three again took up the journey, keeping a sharp lookout for anything that might prove of interest.

They found something before they had gone another mile.

Coming up the trail at a slow, leisurely gait was a large donkey, on the back of which rode an Indian man, woman, and two half-grown children. But something else amused the chums more. In pouches secured to the mule’s sides were two other Indian children, their faces sober as they looked upon the whites.

“Where’s a movie camera?” demanded Bob quickly. “I’m going to take a chance with them. They can’t do anything to us.”

“Here.” Joe had removed a camera from his pocket and was turning the crank and exposing several yards of film. “This ought to be interesting on the screen,” he said.

Much to the youths’ surprise, the Indians did not protest at having their pictures taken. They merely stared at the whites in wonder.

“Maybe they haven’t seen a camera before, and don’t know what it’s all about,” was the opinion expressed by Joe.

A little later they came to a flat field, which was being cultivated by an Indian with a team of oxen and a crude wooden plow. It was an interesting sight. The slow animals drew the improvised instrument steadily through the hard soil, while the sober Indian watched closely.

“More movies,” sang Bob, bringing out his camera. “Every little bit counts.”

Again they were surprised to see that this Indian displayed no indignation at the whites taking pictures. Perhaps after all Joe was right and the Indians in this section were not familiar with a camera.

The adventurers had been driving their pack animals ahead all afternoon when suddenly they rounded a bend and came to a narrow river.

“Look!” cried Joe quickly, pointing ahead. “What’s that on the bank? Why, it’s bones!”

Dr. Rander had heard.

“Llama remains,” he explained. “Looks like llamas have picked this spot to die on.”

Scattered thickly over the river bank were scores of white bones, which undoubtedly were those of llamas.

“I knew elephants occasionally have a cemetery, but that any other animals do I had not the slightest idea,” said Joe.

More movies were taken, and then they set about to devise a means to cross the river.

“We’ll have to ford it,” announced Dr. Rander, who had been waiting for the chums to walk on up to the head. “I don’t think it is so deep as to cause us trouble.”

Although the weather was warm, Bob and Joe chose to put on their hip boots, to escape the chill that might otherwise result.

They found that Dr. Rander was right. The river was barely three feet deep and was comparatively calm. So they had little difficulty in driving the mules across.

From the opposite bank two trails branched off up the mountainside. The one that was most difficult to follow, Dr. Rander chose.

“From here our going will be more arduous,” he told the young men. “The mountains are steeper, and more obstacles will stand in our way.”

Bob had followed the pack train to a height where he could command a good view of the surrounding country when suddenly he cried out in pain.

“My foot!” he groaned, when the others rushed to his side. “Something bit it.”

“What was it? A snake?” Joe demanded anxiously.

“Let me have a look at it,” the old man said, tying the foremost mule to a gnarled tree.

When Bob removed his legging and sock, he found a large red scratch, and the flesh about it was already badly swollen. It pained severely and throbbed so violently that the boy could hardly hold his foot still.

“Not a snake,” Dr. Rander told him. “Rather a poisonous insect—they are common in the Andes.”

The old explorer bathed the foot in water from a canteen and treated it with antiseptics, wrapping it up firmly.

“Now until that heals some you’ll have to ride your mount,” Dr. Rander said. “Don’t take no from him for an answer. Get on him and make him carry you forward.”

While Joe and the old man held the mule securely, Bob mounted and with drawn reins held the animal at a standstill.

“Hurrah!” yelled Joe. “You’ve made him give in.”

“Not altogether,” Bob said. “But I think I can manage to stay on.”

At the end of two days of riding the mule, Bob was convinced that the animal was not really as balky as he had at first supposed. Over high hills and rocky paths he carried his rider, until at last Bob’s foot became well enough for him to walk.

“I’ll sort of hate to do it,” laughed the youth, when they were camped under a high overhanging rock.

“I know,” said Dr. Rander. “But there isn’t much choice in the matter. After all, our mounts are not to be ridden except in such an emergency as this. They tire too easily when on the rocky trails, and it isn’t best to put much of a load on them.”

On, on the little party plunged, into the heart of the mountainous region. On every hand they saw something to hold their interest.

They had been on the trail about four days when they saw something that was indeed unusual.

Moving leisurely up the narrow path were eight or ten large Indians carrying an old organ. Ropes were tied tightly around the instrument, and to these the Indians held with a death grip.

Where they were taking the organ, the whites could only guess. Perhaps it belonged to a plantation owner, who wanted a musical instrument in his house.

Suddenly, unexpectedly, one of the Indians cried out in fright, and then there came other cries.

“The organ’s slipping!” shouted Joe. “It’s going over the cliff! And oh!”—he gasped for breath—“it’s taking one of the Indians with it!”

---

THE sight that the explorers beheld was unpleasant to the extreme. Scarcely had Joe uttered the cry of horror when the organ suddenly fell, pushing one of the natives over the cliff.

The man screamed in terror and then disappeared into the depths below. It was thousands of feet to the bottom of the abyss, and instant death was almost certain.

Bob drew back from the brink with a shudder. Joe and Dr. Rander gave cries of repugnance. The other Indians screamed hoarsely, uttering something that only Dr. Rander understood.

The natives ran wildly down the trail, scowling and making gestures.

“Terrible!” muttered the old explorer, when they had disappeared around a turn.

“What did they say?” inquired Joe, who had been struck by the Indians’ attitude of anger.

“They intend to kill the man who wanted the organ,” Dr. Rander told him. “They blame the Indian’s death on him.”

“Well, of all things!” exclaimed Joe indignantly. “Isn’t there anything we can do about it?”

The old man shook his head.

“When they set their minds on anything there’s no use trying to change them,” he said hopelessly.

“We might warn the man whom they intend to kill,” suggested Bob Holton.

“Don’t know who it is,” Dr. Rander returned. “And the Indians wouldn’t tell us.”

Bob and Joe all during that day felt that something could have been done to prevent the natives from killing the plantation owner, or whoever it was that was getting the organ. They were not a little vexed at Dr. Rander for treating the matter so lightly.

“But then,” said Bob hopefully, “maybe the Indians didn’t get away with it.”

Ten minutes later the youths forgot about the incident. They had been struggling over an exceedingly rough stretch when they suddenly came to another river, much wider than the one they had seen several days previously.

“Have to ford it, I guess,” said Joe Lewis. “No other way across.”

Again the boys put on their hip boots, and again they plunged into the water, driving the mules before them. The going here was difficult, as the current was rather strong, and the mules had to be watched more closely.

They were about halfway across when the old explorer cried out in fright.

“Help!” His voice was wild with terror.

“What is it?” demanded Joe, who was nearest him.

Then the youth saw. Dr. Rander was rapidly sinking into a hole. Already the water had reached his chest, and he was going down rapidly.

Joe at once put thought into action. He dashed over to one of the mules, opened a bag, and began searching about for a rope.

Frantic with the delay, the youth worked his hand like a machine, feeling in every corner of the bag. What if he could not find the rope?

But fortune was with him. In another bag on the opposite side of the mule he found the rope. Luckily it was not tangled.

Joe was almost afraid to turn for fear Dr. Rander would be gone. His heart gave a leap as he saw that the explorer’s head was still above the water.

“Here, get hold of this,” Joe called, throwing the rope over to the old man. “Now come on, Bob. Let’s pull.”

This last was unnecessary, as Bob was already on the spot waiting to catch hold of the rope.

“Steady, now!”

Slowly the youths pulled their friend out of the heavy mud, which oozed ominously as it released its victim. Once it seemed as if the old man would have to release his hold, but he managed to hang on desperately.

At last, when he was completely out of the mud, he moved over to his young companions and gazed at them gratefully.

“You did wonderful,” he commended. “Many people would have acted more slowly—and I would have gone under.”

“Wonder if there are any more treacherous places like that?” Bob scanned the chocolate water closely, as if by instinct to detect any dangerous spots.

“We’ll have to risk it,” Joe said. “It might be well to spread apart, so if anyone gets caught, the others can come to his rescue.”

“Good suggestion,” praised Bob. “I’ll get away over to this side.”

But if there were any more mud holes the explorers failed to come across them, and finally reached the other side safely, driving the mules before them.

On the bank Dr. Rander took off his mud-soaked clothes and replaced them with dry ones. Then, after a short rest, they resumed the journey.

“Who’s coming?” Joe strained his ears to make out the source of footsteps.

Then, rounding a growth of stunted trees, appeared a long caravan of small llamas, which were heavily loaded with what was probably firewood. Beside the curious animals walked two Indians, wearing the common “pancake” hats.

Luckily there was enough room for both cavalcades to pass freely, and they experienced no difficulty.

The natives stopped for a few minutes and conversed with Dr. Rander, who spoke Quichua freely. Then they started down the trail, driving the llamas at a rapid pace.

“Funny animals,” observed Bob when they had gone. “I was afraid all the time one or two would come at me and spit in my face, like the one back at Cuzco.”

Joe laughed.

“As long as you don’t bother them, I guess they’re all right,” he said. “But from what I’ve heard, they don’t like to be played with.”

“Don’t I know it!” grinned the other youth.

Before long they saw the origin of the llama caravan. Set back from the path was a large mud hut, about which played several Indian children. Another man and a woman came out to meet the adventurers.

Again Dr. Rander stopped to converse in the Quichua tongue. But not for long. He was anxious to lose no time in getting to the secrets. Even at best it would require many, many days.

“Hope we don’t have any trouble from now on,” said Joe, as he followed the old man up a steep slope. “But I suppose we will.”

Bob nodded.

“Exploring has its difficulties,” he said. “It will be funny if we don’t have any more things happen to delay us.”

That evening they camped in a little valley between two high peaks. All were glad to rest their tired limbs after such an arduous day over rocky paths.

At a small gurgling spring but a short distance away they drank freely and filled their canteens to capacity. Then, refreshed and ready to prepare the meal, they were about to head for the tent when Dr. Rander noticed something coming at them. He turned about quickly, his face white with fear.

The youths saw the danger and ran toward the mules as fast as they could.

Advancing toward them was a heavy swarm of green jungle flies, whose bite all knew to be poisonous as well as annoying. If the flies attacked the explorers, the result would be marks and red, swollen scratches that would disappear only after several weeks of patient treating.

“The mosquito nets—quick!” cried Dr. Rander, opening a pack and fumbling about nervously. “We must have them! That swarm of flies is so large that there won’t be anything left of us!”

But the adventurers were not quick enough. Before they could get out the nets the buzzing flies were upon them, biting their faces and arms severely. The little insects even penetrated the heavy clothing in a determined effort to satisfy their thirst for blood.

“This is awful!” groaned Bob, working feverishly to find a net.

Scarcely would they put a hand into the packs when they would have to remove it and slap away the flies, the marks of which already pained severely.

At last Joe found the pack that contained the nets, and lost no time in distributing the latter among his friends and himself.

“Now let them come,” challenged Bob, facing the swarm angrily. “I guess it won’t do ’em any good now.”

But even with the protection afforded by the closely woven nets, the menacing little creatures bit the explorers’ arms and legs most annoyingly.

Relief did not come until dark. The blackness of the night served in some manner to cause the flies to leave, although a small few remained threateningly.

“Oh!” muttered Bob, trying in vain to bend his wrist. “They sure fixed us up plenty good. Our—— My gosh! Joe, look at yourself in a mirror. And you, too, Dr. Rander.”

The three were indeed a sorry-looking sight. Their faces were so swollen that their eyes were hardly visible, and their hands and arms were no better off.

“And how it hurts!” Joe was almost frantic with the stinging pain. “It’s a good thing the sun went down when it did, or there would have been nothing left of us,” he added.

All were too bruised and tired to prepare a meal, but necessity forced them to do so. But not until Dr. Rander produced a large tube of a special salve, which he applied freely to the swollen parts.

“This will relieve the pain,” he told the youths. “In the morning we’ll be a little better, but it won’t be for a week that the sores will disappear completely.”

Dawn found the adventurers scarcely aware that they had been bitten, although the scars were still there to tell the story.

“Let’s forget all about that unpleasant encounter,” suggested Joe optimistically. “Suppose we take everything that happens purely as an adventure.”

“Now you’re talking!” Bob patted his chum on the back. “We came here for adventure, and we mustn’t kick when we get it.”

Along toward noon Bob was lucky in bringing down a wild duck, which flew from a jungle not far away. Roasted over a fire, it proved good eating, despite the fact that it was tough.

Dinner—for that was what the youths called the noon meal when they were on exploration trips—over, they took it easy in the shade of a group of stunted trees, which grew almost straight out from the mountainside.

“Trail’s pretty bad,” observed Joe, his eyes on what could be seen of the narrow path as it circled up the peak. “But I suppose it’s nothing to what we’ll find it later on.”

Which proved fairly accurate, as they later observed. At times the trail was so rough and rocky that it was with greatest difficulty that the mules were able to clamber up the steep elevations. On one occasion it was necessary for the mules to jump up a three-foot rock, which obstructed the trail dangerously near a five-hundred-foot drop.

“Steady, now,” cautioned the old man, helping the youths unload the mules. “If we make a misstep, it will prove our finish.”

None of the explorers did, fortunately. But one of the mules was not as lucky. It was the last animal in the line and had been carrying only trifles that were not of necessity to the explorers.

The other mules had safely jumped to the top of the rock and were grazing on the thin patches of grass that grew on the mountainside.

“Hurry, now,” came from Joe. “Let’s get this last fellow up.”

Scarcely had the words left his mouth when the unfortunate animal lost its footing and, balancing for a moment at the edge of the canyon, plunged helplessly over the brink.

“Gone!” Dr. Rander could hardly believe the fact.

Bob and Joe had watched the accident tensely, unable to render any assistance to the terrified mule. At last they climbed up on the rock with a resolution to take matters as they were.

“Talk about adventure,” said Bob with a grim smile. “I guess we’re getting plenty of it.”

“Just wait,” murmured Joe meaningly. “This won’t be anything to what’s coming, or else I’ll miss my guess.”

“I sincerely hope nothing else will happen today,” Dr. Rander said. “I wish to get beyond this short range of mountains before nightfall.”

They later saw that traveling was so slow that it would be impossible to do this. But they were well on the other side of the peaks when darkness overtook them.

“Now to make camp,” sang Bob, tethering the foremost mule to a stout crag.

“Wait,” called Joe, who was just out of sight around a turn.

“What for?”

“Because—I’ve found something. Come here.”

Bob and Dr. Rander went around the bend, where Joe was waiting for them.

“It’s a cave,” explained the youth. “A big cave. Let’s see what’s in it.”

“Better be careful,” was the old man’s warning. “It isn’t unlikely that some snake has its lair here.”

They went in cautiously, Joe holding his flashlight and Bob his revolver. How far the opening extended they had not the slightest idea, for the light beam did not reach the other end.

Suddenly Joe shrank back, as his light rested on something not thirty feet ahead.

“Bats!” he cried. “Vampire bats! And they’re coming toward us!”

---

TURNING on the moment, the three ran toward the entrance of the cavern, never looking behind for fear of seeing the ugly creatures dangerously near.

“They’re coming!” panted Bob, as he heard the flapping that told that the bats were flying nearer. “And I do hope we can get out in time!”

They reached the entrance of the cave and dashed out, but not before one of the creatures had inflicted an ugly bite on Dr. Rander’s leg.

Once out of the dark opening, the adventurers felt fairly safe, even though several bats followed them.

“We can at least fight them off out here,” said Joe. “And that was something we couldn’t have done in the cave.”

The several bats fluttered about ominously, keeping close to the ground. Their faces were of peculiar shape, closely resembling that of a bulldog. What interested Bob and Joe was that the creatures could run very rapidly over the ground.

“Usually bats can’t make much speed except in the air,” remarked Bob, remembering something his father had told him. “Their legs aren’t ordinarily made for walking.”

“It’s different with these vampires, though,” came from Joe.

Dr. Rander thought it best to proceed farther before making camp, in order to protect the pack animals from the bats. He well knew that it is not uncommon for mules and llamas in this region to be attacked by bats. People, however, are usually safe from their bites.

That night the mules were molested only slightly by a few of the bats that followed the expedition. But aside from a few swollen places, they were none the worse for their experience.

“It’s a wonder one of us hasn’t a place or two to show that the bats were around,” remarked Joe, after, the morning meal.

“We have.” Bob glanced at the old explorer. “At least Dr. Rander has.”

That person had been treating the wound in his leg and watching it closely to see that infection did not set in. The right kind of care, he said, would cause the sore to heal quickly.

Again up the difficult trail the explorers went, after having broken camp and attended to the mules.

“Wouldn’t be funny if we’d meet anything here,” said Bob with a shudder. “The path is so narrow that it’s all we can do to get by ourselves.”

“No,” Bob agreed. “And there’s no way of telling——”

He did not finish the sentence, for at that moment there came a commotion from around a turn. To the travelers, it sounded like rapidly moving hoofs.

The noise increased. Then the three shrank back as they saw advancing toward them a line of galloping vicugnas, which were small animals resembling llamas.

Joe groaned hopelessly.

“Either we or they will have to go off the cliff,” he said tensely. “There isn’t room for both of us.”

The animals came nearer at a rapid pace. Apparently they were greatly frightened from some cause or other. Whether something was chasing them the travelers did not know.

“We must save the mules!” cried Dr. Rander anxiously.

“I have an idea, if it will work,” said Bob.

The other looked at him hopefully. Well they knew that if the pack animals were to plunge over the edge of the peak, the three would be faced with the possibility of starvation.

There was not a moment to lose. Whatever they did must be done quickly.

Bob moved over to the head of the pack train. Joe and Dr. Rander remained near the middle of the line, intending to frighten the vicugnas and prevent the pack animals from becoming panic-stricken. If necessary, they would shoot the vicugnas to prevent them from coming around the trail. But unless forced they did not wish to do this for fear of scaring the mules.

In front of the foremost pack animal Bob stood with a thick rope, which he had formed into a lasso. When the first vicugna came near, the youth swung the loop out from the side of the mountain and made a perfect throw over the animal’s head.

Bob gave the rope a quick pull and then let go. The impact brought the vicugna to the ground with a thud. Its followers, trying in vain to check themselves, stumbled over their fallen leader, several of them falling over the cliff. The others remained on the trail with difficulty.

“Fine work!” praised Joe, walking around the mules to his friend. “If you hadn’t thought of that, I guess we’d have had to shoot them. I didn’t know you knew anything about a lasso.”

“I don’t. That is—very little. But I thought I’d try that and see if it would work. If it didn’t, I was going to shoot them. They had to be stopped some way.”

“What do you suppose made them come around the trail so fast?” asked Joe.

Dr. Rander expressed the belief that the vicugnas had been frightened by a puma or some other animal.

“Otherwise they would not have made that wild dash,” he said. “Whenever you see a stampede of animals, you may know that there is some reason for it.”

The explorers forced the remaining vicugnas to turn back and follow the trail in the direction from which they had come. When the last animal had disappeared around the bend, Dr. Rander urged the mules ahead, and they again took up the journey.

“I don’t suppose the puma or whatever it was will frighten those vicugnas back again, will it?” Joe was a bit worried as they labored around the rough trail, which was even narrower than before.

“We’ll hope not,” the old man said.

“If the puma’s there, maybe we can get a shot at it,” suggested Bob. “I’d like to bag one for Dad and the others.”

But if there was one of these huge cats in the vicinity, it did not make its presence known. Perhaps, as Joe mentioned, it had left for another locality.

So closely did the youths look about that they did not notice the wall of rock that appeared suddenly before them. Only Dr. Rander’s voice served to rouse them.

“Here we come to the first secret,” he asserted, pointing to a small opening in the wall of rock.

“So soon?” asked Bob wonderingly. “Why, I thought——”

“It is a tunnel,” explained the old explorer. “One that was made by the Incas. As far as I know, I am the only person who is aware of its existence.”

At once the boys were aflame with interest.

“And—and we must pass through it?” Bob peered at the narrow opening, which seemed no different from many other crevices they had seen.

“Yes. There is no other way to reach the cave of gold. At least not from this direction.”

The adventurers got through the opening easily, but the mules experienced more difficulty. And they did not at all like the idea of plunging into a dark tunnel.

But finally they were forced through by Joe, who had gone back outside. Then, with the aid of flashlights, the party proceeded to thread their way in the narrow passage.

“How much of this is there?” asked Joe, when fully five minutes had passed.

“At least a mile more,” Dr. Rander returned. “It is very long.”

But if it were a mile, it seemed to the youths like several times that much, for in the damp, odorous tunnel the time passed very slowly.

“Will we ever reach the other side?” Joe was tiring.

At last the passageway became light, and then an opening loomed up and let in the fresh air of the outside.

“Hurrah!” Joe was delighted. “But—where are we?”

On all sides of the travelers were towering peaks more lofty than any they had yet seen. Some of the mountains were narrow and pointed, with snow at their summit; others were merely huge rounded mounds of rock. All were magnificent, inspiring thoughts of grandeur.

The youths and the old man were on a narrow shelf that was perhaps five thousand feet above what looked like a tiny winding ribbon of water. It passed in and out among the mountains, stretching far out of sight in the distance.

“That is the Apurimac River,” pointed out Dr. Rander, following the boys’ eyes. “It turns on northeast and finally comes near Mount Panta——”

“That’s where Dr. Rust and the other archæologists are,” interrupted Bob, and then added: “Wonder if they found any Inca ruins?”

“There are many that we know nothing about,” the old explorer said. “Peru and the Andes literally teem with fascinating ruins. Perhaps there are more treasures, too.”

Bob resolved to venture a bold question.

“How did you come to find this treasure cave?” he asked Dr. Rander. “If you don’t mind telling us.”

“Not at all. It might interest you to know that I first found that very tunnel that we just passed through.” Dr. Rander pointed to the entrance into the passageway, from which they had emerged. “I happened to be camped not far away from that crevice in the mountainside that we first saw. It seemed no different from other cracks, and at first I thought nothing of it. But when I lingered about awhile I saw that near the top the rocks were smoother than I usually found them. This made me wonder if the opening were natural or man-made. My curiosity got the better of me and prompted me to go through and see if I could find anything unusual. Then I discovered the tunnel.”

He paused, apparently finished.

“Then what? Is the cave near us now?” Joe was breathless with interest.

“The treasure, you mean? No. It is many miles from here. Look,”—he pointed around the mountainside—“see that winding trail? That is a secret known only to us. It alone can take us to the place we’re after.”

Joe sighed submissively.

“The old Andes are too much for me,” he said. “I had no idea they were as large and vast as this.”

“You will see even more wonderful sights,” Dr. Rander told him. “And before we go many miles farther.”

Indeed the boys found much to hold their interest. The awe-inspiring cliffs, the stupendous rocky crags, the foamy river below, the breath-taking heights—all these held a certain fascination for the two youths. They found themselves absently bending their efforts too much on seeing the sights and not enough on making out the dangerous trail.

“Be careful here,” Dr. Rander warned, as Joe almost slipped and fell. “It surely would not do to roll down this steep slope.”

“That would about put an end to everything for me,” said Joe with a grim smile.

The trail curved on up the mountainside until it reached a high pointed crag, which had been visible for several miles. Then it gradually circled around until it reached the base of the mountain.

“What’s that noise?” demanded Bob Holton, stopping quickly to listen to a deep rumbling sound that increased with every moment.

Dr. Rander looked up. Then his eyes opened wide with terror.

“It’s an avalanche!” he cried hoarsely. “Tons of rocks are coming down at us!”

---

OVER their shoulders the youths glanced up the mountainside and to their horror saw that the old man was right.

Far up the slope was a great mass of stones and earth, rolling down in a heavy cloud of dust. Every second saw the accumulation nearer and larger. In but a brief time it would be upon the little group below.

“We must do something—without delay!” Dr. Rander’s voice was cool and resolute. “The mules—they must be pushed out of the way!”

Acting on the instant, Bob and Joe and the old man worked like madmen to drive the pack animals over to a flat shelf that was but a few hundred feet away. Even this did not offer absolute safety, for the mass of rocks and earth might change its course and plunge down on the shelf.

“We’ll have to take a chance,” Bob panted. “Most likely over here we’ll be out of the danger zone.”

The flat stretch offered the only place of refuge. If the avalanche should change its course, the adventurers and their pack animals would surely be crushed.

There was a moment of fearful waiting, a brief period when the hearts of all stood still, and the huge mass of rocks roared past and on down the mountain slope.

“Thank goodness!” breathed Dr. Rander. “A narrow escape if there ever was one.”

Their eyes followed the plunging stone heap until, with a dull thud, it struck the bottom of the abyss, far below.

“If that had struck us we’d have been smashed to pulp,” muttered Joe with a shudder.

“Think of something more pleasant,” smiled Bob. “The treasure, for instance.”

That afternoon the three were struggling along the narrow path when suddenly Bob caught sight of something up on a high shelf.

“Look,” he said, pointing up to the flat stretch. “Inca ruins as sure as I’m born.”

“You are right,” Dr. Rander assured him. “That building is an ancient temple, where the Incas worshiped the sun god.”

“Sounds interesting,” Joe said eagerly. “Why can’t we go up there and explore the place?”

“Can if you want to,” the old man replied. “I have been up, but I will go again with you. Wait until I tie the mules.”

It was a difficult climb to the shelf. All were gasping for breath when they finally reached the ruins.

Those ruins the youths found interesting. The building was partially intact, being constructed of huge stone blocks cemented together with mud. It was shaped like a pyramid, the sides sloping up to form a point at the top. The entire north end was in ruins, but the other sections looked as if they had been built but recently.

“Let’s go inside,” suggested Bob, looking at the dark opening that once no doubt was closed by a door.

The others agreed, and, led by Bob, entered the building. As the windows were large and there was no covering over them, the adventurers could easily see about.

They were in a large room, over which was an unusually high ceiling. Several stone implements were scattered about; what they were doing in a temple, the boys could not guess.

“Perhaps this was meant for a storehouse or some other kind of building,” thought Bob, but did not say so. He did not wish to conflict with Dr. Rander’s opinion.

But aside from these few stone objects, there was nothing in the building that was of particular interest. Whether the structure had been deserted by the Incas, or whether someone had robbed it of its former contents, the youths did not know. Surely, if Dr. Rander was right in his belief that he alone knew of this trail, no one had been here.

They explored the building eagerly in search of anything else that might have escaped their view before.

“Ouch!” cried Joe, slapping his leg. “What was that that bit me?”

“Oh, I should have told you,” began the old man with a smile. “There are fleas here.”

“What th——” Joe was perplexed. “Fleas? What do they live on? There isn’t anything in these ruins——”

“That is out of my knowledge,” Dr. Rander said. “I never have found anything yet that they might eat. Unless it would be other fleas.”

There was a general laugh.

“Whatever it is, it’s enough to keep them alive,” observed Bob, scratching his arm. “At least as long as we stay they’ll be able to secure a good living.”

“Suppose we get out and don’t stay any longer,” was the suggestion made by Joe Lewis. “There isn’t anything here——”

“What’s that?” cried Bob suddenly, interrupting his friend.

Bob had heard a peculiar noise that caused him to turn about.

Again it came, a hideous hiss that made them jump in alarm.

“Snake!” pronounced Dr. Rander, and an instant later a long slim body unwound itself and made slowly toward the three explorers.

“It’s poisonous, all right,” observed Bob, noting the peculiar shape of the reptile’s head.

“And we haven’t a gun!” moaned Joe ruefully. “What will we do?”

“You mean we haven’t a rifle, but we have a gun.” Bob produced his revolver, which he aimed carefully at the horrible staring eyes.

“I won’t dare miss!” he thought, and then pulled the trigger.

The report of the pistol mingled with a sickening swishing noise as the snake lashed about in its death struggle.

“You got him, all right.” Joe felt a refreshing feeling of relief creep over him.

Bob nodded.

“Let’s get out of here,” he said in a determined voice. “There’s no telling how many more of these creatures we may see if we don’t.”

“I should have brought the movie camera,” laughed Joe, as they descended the hill. “That would have made a peach of a picture.”

“I’m glad you didn’t,” came from Dr. Rander. “Because the sight of those ruins might have inspired some scientists to come over this trail. And the secret treasure cave might be known to them—if they could open the hidden door.”

Dr. Rander, however, had not protested to the youths’ taking movies of the region they were passing through, even though there might be danger of someone from the United States coming in search of other ruins and treasure hideouts.

“I could not say anything against your doing that,” he had told them. “Especially since you were engaged by the motion-picture house.”

So they had exposed film whenever they thought it advisable and were well pleased with the results so far. All told, they had already cranked off more than a thousand feet of film, and fully expected to use that much more.

“These scenes ought to be interesting, too,” remarked Bob, untying the foremost mule. “I believe the Neuman Motion Picture Corporation will be well satisfied with them.”

“Let’s hope so,” Joe said. “The money we get from doing this is no small sum.”

The next day they plunged into a region that was wilder and more dangerous to penetrate than any they had been in before. The rugged Andes reached up on all sides of them, often forming narrow valleys that were shut off from the rays of the sun.

“Sure is cold tonight,” remarked Joe with a shiver.

They were camped beside a small spring that was fed by an underground stream. Darkness had fallen, and with it had come the chill of the Andean night.

Joe was resting peacefully beside the warm blaze of the campfire when suddenly he caught sight of two small fiery lights coming slowly at him.

---

JOE’S first impulse was to get to his feet and utter an exclamation of alarm. But he knew that this sudden movement might cause the creature, whatever it was, to rush at him.

His rifle lay at his side for just such an emergency as this. Thankfully Joe raised the gun, took aim, and fired between those two lights, which had now taken the form of eyes.

Bang! The shot broke the stillness of the night and sent Bob and Dr. Rander scurrying over to their friend. They had been on the opposite side of the fire and had not noticed Joe’s movements.

“What is it?” Bob was all excitement.

“Don’t know,” his friend replied. “Let’s see.”

The sound of the gun had not been followed by any other noise. Evidently Joe’s aim had been true, killing the creature instantly.

Bob produced a flashlight, which he turned in the direction in which his friend had fired.

“Why—it’s another snake!” exclaimed Dr. Rander. “A bola. It isn’t poisonous, but it is a good thing you got it. There is no way of knowing what it might have been.”

With the aid of the flashlight they examined the reptile closely. Its head was almost shot off, making it useless as a specimen.

“I’d like to have it for Dad and the other naturalists,” remarked Bob. “But as it is, guess it’s no good for anything.”

“You should have been more careful in shooting it,” teased Dr. Rander. “Now if you had aimed at its body instead of its head——”

Joe smiled.

“A snake has eyes in only one place,” he said laughingly, “and the eyes are the only part of it you can see at night. Now if this fellow had worn a badge to signify that he was a member of the Royal Order of Andean Reptiles, maybe the fire shining on it would have given me a good place to take aim at.”

“Probably wouldn’t bother with him anyway,” said Bob. “After all, we’re out to find the treasure.”

Nothing happened that night to disturb their slumber. They awoke the next morning eager to continue the journey.

“Today we should come to the big secret,” Dr. Rander told them during breakfast. “If all goes well, we should get there this afternoon.”

Bob was restless.

“Let’s hurry and get going,” he urged, untying the mules.

Farther over the rocky trail the three adventurers trudged, keeping a sharp lookout for anything unusual.

Always in the distance were massive snow-clad peaks, which on this morning were enshrouded in a heavy mist. Usually they were plainly visible, especially through the high-powered binoculars that were carried by Joe.

Gradually the path spiraled down the steep slope until it passed through a narrow valley, which was green with a variety of luxuriant vegetation. So dense were the plants that they almost formed a jungle.

“Look at this,” cried Bob, moving over to a vine that was laden with large red berries. “Wonder if they’re good to eat?”

“Yes.” The old man had broken off a branch and was eagerly partaking of the fruit. “They are wild cherries, or tomatoes, as some call them. There is nothing better for taste.”

“Right you are!” agreed Joe, after he had eaten several of the berries. “They’re fine!”

They picked a sackful of the fruit to have at the noon meal. Then they resumed the journey.

At places the trail was overgrown with weeds and grass, making it difficult to follow it. But Dr. Rander had been through this region before and did not hesitate long in picking out the right branch.

“I don’t see how you can remember the way,” Joe told him, when he had pointed out one of three branches, each of which was almost parallel to the others.

The old man laughed.

“I can’t afford to forget,” he said. “All that treasure is something that is worth too much to be forgetting where it is. If it should happen, though, that I should get turned around, I have a rough sketch map of this region that I made at the very start.”

On the other side of the valley was a steep slope that was entirely devoid of vegetation. Look about as the youths did, they could see no path. They were beginning to wonder when Dr. Rander broke the silence.

“From here there is no trail,” he explained. “We’ll have to cut our way through the hard places and climb over large rocks. It won’t be easy, but we will be rewarded.”

“No trail, huh?” thought Bob. “Here’s where the fun begins.”

It was far from fun, in the usual sense of the word. The three labored over short, steep elevations, rocky precipices, narrow ridges, pulling the sure-footed mules behind them. At last, when they finally reached a high ledge, they sat down to get their breath.

“Whew!” gasped Joe, wiping the perspiration from his brow. “I don’t want much of that. Wonder how old Dr. Rander stands up under such a strain?”

“Hardened to it, I suppose,” was Bob’s reply. “Since he left college he’s been nothing else but an explorer.”

The old man had been at the back of the line, attending to the last pack animal. There was a smile on his face as he approached his young friends.

“We’ve made unusually good time,” he said, sitting down beside them, “and we can afford a rest.”

“We earned it, all right,” came from Joe. “How much more of this is there?”

“A long stretch,” Dr. Rander responded. “Several miles, to say the least. Of course,” he added, “it would not be long if we could go in a straight line. But over mountains and around cliffs the going is much different.”

“I’ll say it is!” Joe was still panting from the difficult climb. The high altitude required an unusual amount of wind.

Fifteen minutes later they were ready to continue. The mules had been coaxed ahead over the dangerous ledge.

“Getting darker,” observed Bob Holton. “Wonder if it’s going to rain?”

Dr. Rander looked up anxiously. Sure enough, heavy clouds were forming above the mountain tops, hiding the sun from view.

“It would not be well for us to be caught in a storm here,” the old explorer said. “We must seek shelter somewhere. It certainly looks as if a storm will be upon us before long.”

They looked about for some place of refuge, such as a cave or overhanging rock. But luck was not with them that day. They had searched an hour under a sky that was rapidly becoming darker when suddenly a terrific hailstorm struck them.

“Quick!” gasped Joe, who was almost frantic. “We must find some place!”

“We’re not finding it,” returned his chum, who was taking the danger more lightly. “And I guess there’s nothing we can do but stay out here in the open and endure it.”

But a few minutes later Bob had become as serious as his friend. Hail as large as marbles was falling with a terrible velocity, striking the explorers’ faces dangerously. One lump caught Joe squarely on the nose, causing him to utter a cry of pain.

“This is awful!” he moaned, holding his hand in front of his eyes.

How long the storm would last they had not the faintest idea. Even Dr. Rander could express no opinion.

Doggedly they fought off the hail, which bruised and cut their faces and bodies. They wondered how the mules were standing it. Could the animals endure the terrific onslaught? Or would they become panic-stricken and plunge off the steep cliff?

After what seemed like hours, the hailstorm suddenly subsided and the sky began to lighten. Ten minutes later the surrounding mountains bore no evidence of the disturbance.

With the adventurers, however, it was a different matter. Their faces were cut in many places, and their clothing was torn. A more miserable-looking trio could hardly have been found.

“Get out the ointment,” directed Bob. “We’ll sure need plenty of it.”

“The mules came through all right,” observed Dr. Rander. “Cut and bruised, but nothing more.”

“It’s funny,” began Joe, looking up at the sun, which was now in full view. “That was a very queer storm. It came quickly and ended the same way.”

“Hailstorms are rather common in this part,” explained the old man, getting out a box of antiseptics and first-aid remedies.

Their numerous wounds were treated with a soothing salve. Then, after looking over the mules, they moved on around the mountainside.

At a huge notch in the rocky slope they stopped to examine a curious formation that puzzled them. It was a long sloping slide, running gradually down the mountainside. From all appearances it was as smooth as glass.

“I don’t know whether this is natural or man-made,” said Dr. Rander. “I never have been able to find out. But,” he went on, “what concerns us is that we’ll have to slide down to the foot of the mountain.”

“What!” Bob’s surprise was beyond words. “Do you really mean that?”

“Every word of it,” was the old man’s reply. His little eyes twinkled. “Don’t you think much of the idea?”

Bob laughed.

“It was so sudden that I hadn’t given it a thought,” he answered. “But”—gazing far down the smooth slope—“it looks rather inviting. Will you go first?” The youth was not fully convinced that Dr. Rander was in earnest.

“If I go, one of you will have to stay with the pack animals,” the old man said. “I don’t think they had better try it,” he added with a laugh.

Bob and Joe looked puzzled.

“I don’t understand,” said the latter, hesitating. “Do you mean that some of us will slide down this slope and some stay with the mules—leave them here, I mean?”

“Oh, no,” smiled Dr. Rander. “One of us will have to take the mules down the trail. We could all go that way, but as it is very long, this offers a short cut that you fellows can take. That is, if you want to. When you get to the bottom you can wait until I get down the trail with the pack animals.”

“Where is the trail?” Bob secretly wondered if Dr. Rander had suddenly changed his mind about sharing the treasure with them and was using this means to evade them. He did not think the old man treacherous, but he wanted to be on the safe side.

“Over there.” Dr. Rander pointed to a narrow path that circled down the mountainside.

“Suppose,” Bob began, “you and Joe go down the slide while I take the mules down the trail. I don’t like the looks of that glassy slope.”

“All right. I’m no longer young, but I still like sport. Here I go.”

The next moment he was sliding rapidly down the polished incline.

When he was halfway down, Bob and Joe burst out in laughter. The sight of the old man doing such a thing as this with so much enjoyment aroused the youths’ sense of humor.

“If he likes it so much, maybe I will,” chuckled Joe, sitting down at the edge.

“Good luck,” called Bob, as his friend let go his hold and passed swiftly down.

It was an unusual sensation to Joe, as he shot down the curving slide. When younger he had often played on the slides in parks. But this was something entirely different. To shoot down a tall mountain at a rapid pace, on the straightaways and around curves, was indeed novel.

When over halfway down, the youth felt himself gradually lose momentum, and he knew that the slide was flattening out. Too steep a descent, especially near the bottom, would be dangerous.

At last he came to a stop beside Dr. Rander, who had been watching the descent.

“How did you like it?” the old man asked.

“All right. Got rather warm, though. Wonder if it thinned my trousers any? No, I guess not. Too smooth, I suppose.”

Fifteen minutes later Bob came in sight leading the line of mules. He laughed as he caught sight of them.

“Any worse for your experience?” the youth asked with a chuckle.

“Do we look it?” smiled Joe. “We enjoyed it.”

As the sun was almost directly overhead they decided to remain at this spot for the midday meal. All were extremely tired and hungry.

Bob prepared dinner, using water they had brought with them in canteens. As a dessert they feasted on the delicious wild cherries that they had picked that morning.

“Now let’s get going,” urged Joe, when the meal was over. “I’d like to see that treasure.”

Farther into the wilds they plunged, with not the faintest suggestion of a trail to guide them.

“No trace of any vegetation here,” observed Bob. “It’s a good thing we stopped where we did, or the mules probably wouldn’t have had anything to eat. There were a few stunted bushes and other plants back at the foot of the slide.”

An hour of climbing brought them to a place where a tall peak obstructed their view.

They trudged around and then suddenly found themselves at the bank of the roaring Apurimac River.

“On a little farther,” Dr. Rander said, urging the mules to ascend the difficult slope.

At last they came to a place where a high rock protruded far over the river. Here the old explorer called a halt and pointed up the side of a mountain.

“In that little notch up there is the entrance to the treasure,” he said. “As I said before, there is a huge cave that occupies the entire mountain. There we will find the treasure, if there is any.”

The youths’ hearts beat rapidly. They could hardly believe that at last they were nearing the great secret.

“But,” hesitated Bob Holton, “how are we going to get across this roaring river?”

“That,” the old explorer returned, “will be the most difficult part of our entire journey. Come. Let me show you.”

They followed him to the edge of a high rock that protruded far out over the seething rapids.

“Look there,” he said, pointing to something.

Stretching from the rock across the river to another protruding crag was a heavy metal wire, which, strange to say, showed not the slightest trace of rust.

“That cable was put there by the Incas,” Dr. Rander said. “It is hundreds of years old, but still looks as if it had been built but yesterday. It is coated with some secret preservative, which prevents it from rusting through.”

“Interesting,” remarked Joe. “But what about it?”

The old man replied at once.

“We must cross the river by hanging from the cable with our hands,” he said quietly.

Joe’s heart sank. Secretly he felt that if he were to undertake the dangerous venture he would meet with tragedy.

---

“CAREFUL, now.”

Dr. Rander was slowly and dangerously hanging from the heavy wire with his hands, working his way steadily across the roaring rapids below. If he were to fall, it would probably seal his doom, even though the youths held one end of a stout rope that was tied securely around his waist.

“Think he’ll make it?” Bob looked on anxiously, half expecting to see the old man let go and plunge into the seething water below.

Slowly but surely he swung across, holding on with a grip of steel. It seemed remarkable that a person of his age could withstand the arduous tasks connected with exploration. But no doubt he was hardened to an eventful outdoor life of adventure.

“He’s over,” cried Joe happily. “Made it all right. Didn’t even threaten to let go. Now I wonder if we can do as well?”

The youths had yet to see.

Joe was next to swing across. He walked over to the cable and gazed doubtfully first at the boiling stream below, then at Dr. Rander on the opposite cliff.

“Go ahead,” said Bob. “Might as well get it over.”

“Yeah. But I wish it weren’t necessary to do this. I suppose, though, that I can do it if Dr. Rander can.”

Joe sat down on the edge of the cliff, took hold of the heavy wire, and slowly let himself down.

For a brief moment it seemed as if his arms would be torn from their sockets, for, although he was not heavy, the strain was very great.

“I’ve got to make it!” he told himself, gritting his teeth. He refused to think of what might happen if he were to plunge into the roaring rapids below.

“Don’t let go, whatever you do!” Bob, on the rock, was holding the rope tightly, ready to pull his friend to safety if the latter should be forced to release his grip.

Joe swung across with a certain determination that was luckily with him in every emergency. He did not look below for fear of becoming frightened.

At last, when he felt that he could stand no more of this torture, the youth felt his foot touch rock, and he knew that he was safe.

“Hurrah!” cried Bob Holton, waving his arms in the air. “Now here I come.”

Bob would find the feat more difficult, since he was heavier than either of the two who had crossed. But usually when he set his mind on doing a thing he was able to do it.

But first he walked over to the mules, which had been tethered securely by Dr. Rander, and got out a stronger rope, which he tied around his waist and shoulders. A small weight he fixed at the other end, and then moved back to the edge of the rock.

“Here. Catch this,” he called, and threw the rope over to Joe on the other side of the river.

When everything was in readiness he slowly lowered himself until he could grasp the wire that stretched across the stream. Then, setting his nerves for the trying task, he let his feet drop.

For one awful minute Bob’s heart stood still. Then he got a grip on himself and swung easily across to the other side.

“That was fine!” praised Dr. Rander. “You never flinched. Now let’s hurry up the mountain to the treasure.”

“Do you suppose the mules will be safe over there?” queried Joe anxiously. “We couldn’t take any food with us across the river. If anything should happen to them——”

“There is no danger,” the old man assured him. “Probably no one has been in this section for years and years.”

Notwithstanding this, the young men were still worried. They realized that they would be in a grave predicament if anything should befall the provisions.

This anxiety gradually wore off, however, as they neared the treasure cave.

“Hard climb, but nothing will stop us now,” smiled Joe happily.

“You will be amazed when you look upon the wonders in the cave,” Dr. Rander told them. “It will exceed your wildest dream.”

“How did they all get there?” inquired Bob.

“I do not know. They were placed there by some wealthy Inca—perhaps a king—for safe keeping. It might have been that this was at the time of the Spanish invasion, and that the owner was later killed by the conquering troops. At any rate, the secret remained as such until I accidentally found it.”

“You sure were lucky,” remarked Joe. “Perhaps it wouldn’t have been discovered at all if you hadn’t located it.”

At a point near the ledge, the mountain grew so steep as to make climbing a very arduous task. A single misstep would have meant a horrible plunge into the roaring rapids below.

At last they came to the top of the ledge, before the notch cut in the mountainside.

“See that dark entrance?” asked Dr. Rander. “That is a tunnel that leads to the cavern. Come.”

The youths followed the old man into the opening, which was made light by the latter’s flashlight. The passage seemed to lead steadily upward, probably into the peak of the mountain.

“Do you suppose this tunnel was constructed?” asked Joe, after five minutes had passed.

“I believe so,” Dr. Rander returned. “When we get farther on, you will think so too.”

Fifteen minutes of walking brought them to the end of the tunnel. From all appearances there was nothing but natural rock before them.

“Watch,” said Dr. Rander, moving over to the end of the cave.

He reached up and pressed a mysterious button. Then he stepped back and waited.

Suddenly the youths gasped in awe, as they saw the huge stone wall slowly swing inward. As it made an opening, a beam of natural light flashed into the cave, making the use of a flashlight no longer necessary.

“Huh! That’s funny!” muttered Joe. “Must be an entrance to the outside somewhere.”

“If you can find it, it is more than I can do,” laughed Dr. Rander.

The opening grew larger, and the light brighter. When the ponderous stone wall had swung away to the utmost, Bob and Joe followed the old man through the entrance.

As they did so their eyes opened wide and their jaws dropped at the sight that lay before them. Ahead was a great stone room, fully fifty feet square, in which were scores of objects carved from stone. Statues of men, birds, llamas, pumas, and many other animals were all about. Ears of corn, plows, chairs, pottery—all these and many more objects were carved out of stone.

It was a wonderful collection, one that would delight the eye of any archæologist. Bob and Joe inspected the various objects with interest, knowing that Dr. Rust and his fellow scientists would give a great deal to know of the existence of this place of wonder.

“All this is very interesting,” remarked the old man. “But what we really came after was treasure—if there is any.”

“Yeah. Where is the place where you said it might be?” Bob was anxious to look for something still more valuable than the stone objects.

“I will show you.”

Dr. Rander stepped over to one corner of the large room, where was a huge statue of a man, perhaps an Inca king.

“Now look closely,” he said, when the youths had followed him.

The old man walked up to the statue and stood directly in front of it. Then he waited.

At that moment something happened that caused Bob and Joe to gasp in wonder. Slowly, surely, the statue sank into the floor until it disappeared from sight. Directly below the resulting opening was a ladder, which led down into another gigantic room.

“Well, of all things!” cried Joe in utter amazement. “That sure is a secret if there ever was one.”

“Let us go down.” Dr. Rander was making his way down the ladder, motioning for the youths to follow.

They did and soon found themselves in a huge cavern cut out of solid rock. Here were more stone objects similar to the ones in the room above them.

“This way,” pointed out the old man, walking over to one side of the cave.

“Wonder where the light comes from?” pondered Bob. “It’s from the outside, all right, but how does it get in?”

Dr. Rander bent over and pressed something in a crack in the floor, straightening up a moment later.

Again the youths were filled with amazement. A huge stone block swung away on unseen hinges, leaving an opening perhaps four feet in width.

“Now we must use flashlights,” Dr. Rander said, stepping inside. “There is no opening to the outside, apparently.”

The beams of the electric torches revealed the fact that they were in another cave.

“Over here,” explained the old man, “is a sort of bin cut out of the rock. It is covered with a stone that I cannot lift. But I feel sure that all three of us can.”

“Let’s have a look at it,” said Bob.

Together they heaved on the stone block with all their strength. Before long they saw that their efforts were not in vain. The stone was slowly slipping from the top of the bin. At length it fell to the floor with a dull thud.

The explorers turned the beams of the flashlights into the opening, looking about eagerly.

“Here’s something,” announced Joe, bringing out a small iron box.

“Open it,” directed Dr. Rander.

Joe did—and then cried out in wonder as he saw its contents.

---

“GOLD!” cried Joe happily. “Gold beads, as sure as I’m alive!”

“And scores of them, too,” observed Bob. “Bet they’re worth hundreds and hundreds of dollars.”

They examined the little objects with interest, joyful that at last their efforts had been rewarded. The beads still shone brightly, although they had been in the cavern for hundreds of years. That they were really gold, no one doubted in the slightest.

“Who put them here?” asked Bob Holton, when they were ready to leave for the outside, the jewel box in their possession.

“The Incas,” returned Dr. Rander. “Perhaps it was an Inca king. At any rate it was someone who was wealthy.”

They looked about for any other treasure that might be in the room, but found none. At last they left the cave, closing the stone door behind them.

Led by Dr. Rander, they climbed the ladder, and then passed through the great room that was filled with the stone statues.

“We must hurry before it gets dark,” said Dr. Rander, closing the secret stone wall by pressing the hidden button. “It will not do to cross that river at night.”

“Bad enough in the daytime,” added Joe, as they made their way through the dark tunnel.

When at last they reached the outside they saw that they had but a few minutes before the sun would sink from sight.

Down the steep slope they climbed until at last they reached the cliff which protruded over the roaring river.

“How are we going to get the jewel box across?” asked Joe. “It isn’t large, but it’s too big to put in our pockets.”

“Use a rope, I suppose,” was the answer from Bob. “We’ll tie it tightly across somebody’s back.”

This suggestion was followed, and before long the three were on the other side of the rapids. They were relieved to find that the mules were resting peacefully.

“I don’t like the idea of crossing that river any more,” said Bob with a frown. “But I would like to go over to the secret cavern again tomorrow.”

“What for?” demanded Joe.

“I have two good reasons,” his friend answered. “First, I would like to take some movies of the place. And the other one is that I’d like to make a detailed map to give to Dr. Rust and the other archæologists. They’ll appreciate it, all right. Be tickled to death to know that we found all those Inca remains.”

The next morning they did as Bob wished and once more swung themselves across the boiling rapids, coming to the opposite side safely.

Motion pictures of the secret cavern and its contents were taken, and then a reliable map was made of the region, including the exact location of the mysterious buttons that moved the large stone doors.

Although Bob was assisted by his friends, he did not have everything completed until noon.

With one last look at the mountain of secrets, the three turned and retraced their footsteps to the river.

“Last time across,” said Joe with a sigh of relief. From the start he had feared the dangerous swing from the cable.

No harm befell them, however, and they reached the other side ready to start the journey to Pasaje, where Karl Sutman would be waiting with his airplane.

“Good old Karl,” said Bob affectionately. “It will be fine to see him again. And Dad and the others. I hope they’re all right.”

“With you on that,” came from Joe quickly.

“It will take us many days to get to Pasaje,” Dr. Rander put in. He intended to go with the youths to that town, where he wished to remain for several days.

“Wonder if we’ll see anything more of interest?” Joe was anxious to observe all that was worthwhile.

“There are other secrets I will show you,” explained Dr. Rander. “But as far as I know there is no more treasure.”

They decided to rest the remainder of that day, for all were tired from the strain. On a little shelf beside the roaring Apurimac they made camp.

“Now lead us to more secrets,” said Bob the next morning, when they were ready to resume the journey.

“I will,” returned the old man.

He kept his promise. Late that afternoon they had been following a narrow trail that curved with the river when Dr. Rander stopped and pointed up to a tall peak.

“Beyond that is a little hidden valley,” he told the youths. “In it is a tall tower that was built by the Incas. As far as I know, I am the only person who has ever found it.”

“Sounds interesting,” said Joe. “Can we go there?”

“Yes. Follow me.”

He tied the mules securely and then began the dangerous ascent of the high peak, Bob and Joe at his heels.

After a half-hour of struggling they reached the summit, which was covered with a thin coating of snow.

“Now, look down,” the old man said.

Far, far below, on the other side of the mountain, was a narrow valley that was green with tropical vegetation. It appeared much lower than might be expected.

“Look away over to your right,” directed Dr. Rander. “See that tall tower?”

“Why—why, yes!” Bob was struck with wonder. “Let’s go down and see it. Have you ever been there?” he asked the old man.

“Not close,” was the reply. “I have only looked at it from a distance. Lack of time prevented me from going over there.”

“We haven’t a great deal of time,” said Joe. “But I wouldn’t miss taking that in for hardly anything.”

He led the way down the steep slope, which required not a little caution. A single misstep would have meant a terrible fall to the bottom of the cañon.

An hour of careful climbing and their feet touched the green grass below. The tower, they observed, was several hundred yards in the distance.

“Probably we will find other ruins near,” remarked Joe Lewis, as they walked toward the corner of the narrow valley.

“Where there is one there is likely to be two,” smiled Dr. Rander. “And maybe you’re right.”

When they came nearer they saw that the tower was at least a hundred feet high. It was built of small blocks of stone, carefully fitted together. Near the base was a heavy growth of vines and creepers, which wound around the tower up to a height of twenty feet.

“Here’s a door,” called Bob, who had gone around the other side. “Let’s go in and see what we can find.”

With the aid of small flashlights they entered the structure and looked about.

Everywhere were cobwebs and other evidences of age, showing that it had not been occupied for hundreds of years. In one corner was a narrow winding stairway, which evidently led to the top.

“Shall we go up?” asked Joe.

“Sure. Why not?” Bob was already halfway up the first flight.

The others followed him, winding slowly up the narrow stairs. They wondered a little if it might be safe to venture up into this time-worn structure.

After what seemed like hours, they left the last flight of stairs and turned to go out on the top floor.

As they did so, they saw something that was horrible and disgusting.

---

LYING about on the stone floor were at least ten human skeletons, which were white with age. They were in no fixed positions, but were scattered aimlessly over the dusty floor.

Bob was the first to break the silence.

“Wonder how they got here?” he asked.

“Perhaps they are the remains of soldiers who guarded this tower,” was the opinion of Dr. Rander. “Here,” he went on, “look at this. It’s a dagger—made of stone.”

“You might be right,” commented Joe. “But then, it’s possible that the dagger belonged to someone who came up and murdered those who were here.”

The explorers examined the skeletons for several minutes before going to the edge and looking down on the surrounding valley.

“Can see quite a distance,” observed Bob, peering out at a distant mountain.

“Yes,” agreed Joe. “There——”

At that moment he was interrupted by a cracking noise, which seemed to come from the tower.

“What’s that?” cried Dr. Rander excitedly.

But when it was repeated, there was no doubt in their minds as to the origin of the strange noise.

“It’s the tower!” exclaimed Bob fearfully. “I hope I’m wrong, but I’m afraid it’s going to fall. Hurry! Let’s get down to the ground.”

The three lost no time in scrambling down the stairs. They reached the bottom in safety, and then dashed outside, Dr. Rander displaying remarkable agility for his age.

Then something happened that filled them with terror. With one last creak, the old tower leaned slowly to the south, poised for a brief moment, and went crumbling to the ground. There was a report like that of a cannon, followed by a heavy cloud of dust and small particles of rock.

The explorers’ hearts were beating like trip hammers; their faces were red with excitement.

“Thank God that we escaped in time!” breathed Dr. Rander. “A few seconds more and we would have been caught beneath tons of rock!”

“And what a death!” muttered Joe with a shudder. “I don’t want to even think of it.”

They sat down on the ground to relieve themselves of the terrible strain. Especially did the old man show signs of exertion. At first the youths half expected to see him fall with heart failure, for he was terribly exhausted.

The rest, however, did him good, and before long he was apparently no worse for the horrible experience.

“Funny that tower should collapse just at this time, isn’t it?” said Bob. “I suppose, though, that it was ready to go at any time, and our weight proved too much for it.”

“That probably explains what happened,” came from the old man. “If no one had found it, perhaps it would have remained intact for many years yet.”

They put in no more time here, but turned and went back to the peak.

Very difficult it was to scale the steep slope, but at last they reached the top and descended to the other side.

“The mules are all right,” observed Bob. “Suppose we get going without delay. I’d like to get to Pasaje as soon as possible. I’m getting anxious to see Dad and the others of the expedition.”

“It will still take time,” Dr. Rander told him. “There are many miles of difficult travel before us.”

And difficult it was. Although the adventurers had previously found it hard to make progress through the rugged mountains, they now experienced even more hindrances.

Unfortunately, Dr. Rander was not overly familiar with this section and often made mistakes in pointing out the best course of travel.

It was not uncommon for the adventurers to come upon heavy forests at elevations of fifteen thousand feet. This surprised Bob and Joe, who did not expect to see trees growing at such high altitudes.

“There really is no such thing as the ‘tree line’ in the Andes,” explained the old explorer. “In fact, it is possible to find forests at unusually high altitudes.”

As they trudged on they came to more wild-cherry plants, the fruit of which they ate hungrily. It was refreshing to have fresh fruit after eating nothing but dried goods.

As much as possible they followed the banks of the Apurimac River, for Pasaje, their destination, is situated just above the point where the stream branches.

As they went farther, the mountains became more lofty, and snow on the summits was more common. They never climbed high enough, however, to come in contact with it.

Suddenly, upon hearing an unusual noise, Joe glanced around, and then gasped in apprehension.

“One of the mules is stuck in mud!” he cried. “Quick! We must do something at once!”

Without delay the old man turned about, walked back to one of the pack animals, and secured a long heavy rope. Then he moved on to the rear of the line, where one of the mules was struggling to free itself from the black bog.

“Bob, you had better come to the rescue,” he said, after a moment of pondering. “You’re pretty good at lassoing, as you showed us several days ago on that narrow ledge. Won’t you try it and see what you can do?”

“Where will I throw the rope, over the mule’s head?”

“Yes. Tighten it around the animal’s neck.”

“But—won’t it choke?”

“Not for a few minutes. There is no other way to pull the mule out. If we go too close we’ll get caught ourselves.”

“All right, then. Here goes.”

Bob took the rope, made a loop, and stepped as near as he thought possible with safety.

“If I miss my aim, I can’t help it,” the youth said, as he threw the lasso.

Joe cried out happily as he saw that the loop went directly over the mule’s head. Dr. Rander’s face also lightened.

All three pulled on the rope with all their strength, but their efforts appeared to be in vain. The treacherous bog had engulfed its helpless victim too tightly.

“We’ve got to get that animal out!” cried Joe, redoubling his efforts. “There’s a lot of valuable supplies on its back.”

But how? They were doing all they knew of. If that were not sufficient, the mule would have to go down.

“We’re losing steadily,” observed Bob grimly. “But I guess we can’t help it.”

Despite their furious efforts to draw the beast to safety, it was sinking rapidly. Already its body was nearly under. In but a brief time its head, too, would be engulfed.

But the adventurers kept up doggedly, determined to win the battle even though defeat was staring them in the face.

With one last effort, they gave the rope a new stronger pull. But it was not enough. The weight of the mule and its burden was too much, and the animal’s head slid horribly into the oozing mud, to disappear forever.

Bob slumped down on the grass.

“We lost,” he murmured gravely. “Now we’re one pack animal short.”

“And there were quite a few valuable objects in the pack, too,” added Joe, “not to say anything about losing the animal.”

“Have to get along some way,” Dr. Rander said. “There is no use in thinking anything more about it.”

“Wonder what the mule thought about when he went under?” mused Joe. “It must have been terrible.”

They resolved to follow the old man’s suggestion and forget the loss as best they could. After all, it was lucky that one of them had not been the victim.

Again they took up the journey, this time keeping a closer lookout for other bogs. But Dr. Rander did not know this region any too well, and could not guide them as surely as he would have liked to.

In the fascinating mountains the time passed rapidly. It was two days after they had lost the mule when Dr. Rander pointed to something in the distant sky.

“That’s a condor,” he said, his eyes trying to make out the flying form more clearly.

“It is at that,” affirmed Bob, looking through his binoculars. “And what’s more, it’s white. A condor real, as sure as I’m standing here!”

“Let’s see,” said Joe, and took the glasses his friend handed him.

A few moments of observing and he nodded, giving the binoculars to the old man.

“You’re right,” Joe said to his chum. “And oh! Wouldn’t our dads and Mr. Wallace like to be here now! A white condor! One of the creatures they wanted most.”

“Maybe we can get it for them,” muttered Bob, grasping a shotgun. “Do you suppose there’s a chance?”

“Not unless it flies nearer,” returned Dr. Rander. “Even then the bird would probably fall to the bottom of the cañon, and that would mean a dangerous descent.”

“I’m going to see, anyway,” Bob persisted, following the soaring form through his powerful binoculars.

“Look what I’ve found,” called Joe, who had climbed down to a narrow ledge several yards below the others.

“Why—it’s a nest,” exclaimed Bob, upon descending to the shelf. “And look at those eggs. Sure are whoppers. Say,” he cried suddenly, “I bet I know everything now. This belongs to that white condor. Look. There’s a white feather. See it?”

“You’re probably right,” said Dr. Rander, moving down to the ledge. “Let us look about more. We may find something else of interest.”

But all searching was stopped a second later when Joe happened to glance up.

“The condor!” he cried fearfully. “It’s coming at us!”

---

THERE was not a moment to lose. With the huge white condor swooping down upon them, the explorers knew that they must act quickly. Unfortunately their rifles had been left on the trail above. Before they could secure the weapons the huge bird would be upon them and would probably use its terrible claws and beak to great advantage.

“My knife is all we have to defend ourselves with,” said Joe, watching the large form advance toward them. “But I’m going to use it.”

The condor came on swiftly. It circled around a few times near its nest and then rushed madly at the little group of adventurers.

Now it was barely ten feet away and coming with deadly aim. In but a brief moment it would be in a position where it could work deadly havoc with its sharp claws.

Joe had his long hunting knife in readiness now, waiting for an opportune moment. Then it came.

The huge white bird was soaring directly above its human enemies. As it dropped lower, Joe lunged forward and plunged the sharp knife through one of the long, thin legs.

Uttering a curious sound, the condor darted away, circled around for a brief period, and then flew at the explorers with a new determination.

One of the horrible claws shot out and caught Joe’s arm, the impact knocking the knife from the youth’s hand. It went hurtling to the bottom of the abyss, far below.

Joe was weaponless, helpless!

New horror crept over him when he suddenly felt himself leaving the ground. Not fifteen feet away was the edge of the cliff! Vainly he tried to escape from the clutch of that formidable claw.

Meanwhile, Bob and the old man were not inactive. They knew that it would only be a short time before their friend would be carried over the brink of the cliff. And that must be prevented at any cost.

Looking wildly about, Bob caught sight of a rock about half as large as a brick. Almost frantic, he picked it up, and with desperate strength he sent it crashing into the condor’s body.

The force was terrific, and for a moment it seemed as if the condor were going to drop. But it righted itself and carried the helpless Joe still farther toward the rocky edge.

“I’m going to try something,” blurted out Bob, his face red with an awful fear. “You run up to the mules and get a rifle—quick!” he said to Dr. Rander.

As a last resort, Bob hurled his hundred and eighty pounds at Joe’s feet, and caught hold with a grip of steel. He wondered if the huge bird could lift both himself and his friend. If it could....

At that moment Dr. Rander scrambled down the rocky slope with a rifle, which he aimed unflinchingly at the condor’s body. The next moment the gun barked.

With a terrific fluttering of its heavy wings, the bird sank slowly to the ground. It touched the hard soil, and then with a convulsive twitch it lay still.

For almost a minute there was silence among the little party of adventurers. They were panting furiously, and their wide eyes had not yet lost their look of terror. Perspiration was streaming from them, making their faces shine gruesomely. It had been one of the narrowest escapes they had had so far.

Finally Joe wiped his face and looked at Bob with intense gratitude. Then his eyes fell on Dr. Rander, whose rifle was still warm from the timely shot.

“I don’t know how to thank you,” he said warmly. “If you hadn’t been so plucky, I would probably be lying in a broken mass at the bottom of the gorge right now. It was simply wonderful!”

“Forget it!” Bob disclaimed any praise offered him. “The only thing now that matters is that you’re alive.”

“Thank Bob for that,” the old man said. “If he had not thrown himself at your feet you would surely have gone over the cliff.”

“But it was your shot that finished the job,” protested Bob Holton. “Even with the weight of both of us the condor was slowly dragging us toward the brink.”

“I’m afraid my bullet would have been too late if you hadn’t done what you did,” persisted the old man.

“All right. Have it your own way.” With a laugh Bob dropped the matter and stooped over to examine the huge white bird.

It must have had a wing spread of over ten feet. Later measurements showed that this was accurate. But what impressed the youths most was its pure white feathers, which looked as clean as if they had been recently washed. The terrible claws and long sharp beak next caught the youths’ eyes, and their respect for the power of this monstrous bird was increased.

“Quite a specimen,” observed Joe. “And speaking of specimens,” he went on, “why can’t we skin it and take it with us? Our dads and Mr. Wallace would sure be tickled. The white condor! Boy! I can just see them giving cries of delight.”

“Nothing to prevent us,” returned the other youth. “We may find it hard to place in our mule train, but we’ll manage some way.”

Bob secured a long knife, and with a skill that he learned while on other hunting trips he cut the bird’s skin open down the breast. A few minutes more and the task was completed.

Without the weight of the body, the skin was light, and they had no difficulty in tying it over the back of one of the mules, which appeared not to notice the extra load.

With one last look at the spot where Joe had almost met his death, they turned and drove the pack animals ahead on the remainder of the journey to Pasaje.

But now they were more anxious than ever to reach their destination and fly with Karl Sutman to the place where their fathers were hunting. With every minute they longed still more to reach the town they were approaching.

“I hope nothing further comes up to stay us,” remarked Bob, as they descended a steep slope. “Somehow I’ve had enough excitement for a while.”

“So have I,” said Joe. “But of course there’s no way of telling what we may meet in these mountains.”

The next day they found themselves in a wide valley, which was covered with a heavy growth of dense vegetation. Tree ferns were quite prominent, growing in large clusters that dotted the valley. Bright flowers were also numerous, some of them unusual in shape and form.

And with this heavy vegetation came several varieties of wild animals, among them being foxes, lizards, guinea pigs, and a host of birds. The youths could easily have shot some, but they did not wish to lose time in doing so.

“I believe we are getting close to Pasaje now,” announced the old man, as he led the way around the winding Apurimac River.

Notwithstanding this, they traveled all that day without coming to the town. Camp was made at a clearing near the stream, supper was prepared, and then all retired, knowing that the following day would witness their coming to their destination.

Early the next morning the young men saw something that thrilled them with delight. They had been breaking camp and were almost ready to resume the tramp when suddenly their keen ears caught the sound of a motor. Looking up, they plainly made out an airplane in the sky above them.

“That’s Karl!” cried Joe joyously. “I wouldn’t be afraid to bet anything that it is.”

“I sure hope you’re right,” came from Bob. “Gee! Won’t it be swell to see him again?”

“Of course there’s a chance that he won’t see us,” said the other boy. “But I believe he will. He’ll be looking around for us closely. Maybe that’s why he’s here now.”

Bob started, as an ominous thought struck him.

“Do you suppose anything’s happened—to our dads, I mean?” he asked in a tense voice.

Joe’s face darkened.

“I—I hadn’t thought of that,” he replied solemnly.

They watched the airplane closely, expecting at every moment to see it head downward.

Then it came.

“Hurrah!” Bob was overjoyed. “Karl sees us, all right. And it’s Karl, too,” he observed, as the monoplane came closer.

As the machine flew closer it circled around the little group below, rapidly flying lower. When within a hundred feet of them, its cabin window opened, and Karl’s face was thrust out.

“Hello, up there!” shouted Bob, and received an answering greeting. But the noise of the ’plane’s engine made it impossible for the adventurers to understand the aviator’s words.

While the three were still gazing up at the huge monoplane they saw something that caused them to look all the closer. They made out Karl’s arm reaching out of the cockpit. Then they saw something white drop toward the ground.

“It’s a small parachute,” observed Joe, his heart beating rapidly. “Wonder what’s tied to it?”

As there was no wind, the object fell in a straight line, the parachute opened and began to float slowly above the onlookers. Before long it came to the ground within fifteen feet of them. Karl had certainly aimed accurately.

“Hurry!” cried Joe. “Let’s see what it is. Maybe something’s happened to our dads or the others.”

He picked up the parachute, at the end of which was attached a small box. Opening it, the youth found a folded paper.

“Quick!” murmured Bob. “Let’s see what he has to say.”

---

RATHER nervously Joe unfolded the paper, hastily read it, and then gave a sigh of relief.

“Nothing wrong,” he told his friends. “Take a look.”

“H’m,” observed Bob. “He only says he’s going to land in a level field about a mile from here, and that he’d better take us up with him from there, instead of waiting till we get to Pasaje. No other place near to land on. Closes by saying everything is all right.”

“So he wants us to go up with him now,” mused Joe. “Doesn’t want to wait till we get to Pasaje. I hate to do that. I don’t like to leave Dr. Rander till we get to the town. It doesn’t seem right to come with him all this distance and then go off and leave him here in the mountains.”

“Don’t worry about me,” said the old explorer quickly. “I have been through these mountains alone many times. I can manage the mules all right. And the town can’t be far away.”

“We’d go with you anyway,” Bob told him, “only Karl says there isn’t another landing place near.”

Without loss of time the three continued toward the level spot on which the aviator had landed, at length coming in sight of the monoplane.

Karl rushed out to meet them, his face bright at finding that all were alive and well.

“You old rascal!” cried Joe, shaking the young man’s hand warmly.

“How’d you know we were here?” asked Bob, who was also very glad to see the aviator.

“I saw you,” Karl Sutman explained. “I thought I’d take a short flight over this section to see if I could locate you.”

“You did, all right.” Joe was delighted. “Found us away out here in the wilds.” He hesitated a moment and glanced at Dr. Rander. But the latter had already been introduced to Karl Sutman, and needed no introduction by the youths.

There was one question in the aviator’s mind that he could wait no longer to ask.

“The treasure you were searching for—did you find any?” he inquired. “And the Inca secrets, too. How about them?”

Bob smiled happily.

“We did,” he answered. “Found both the treasure and the secrets.”

When shown the little box of gold trinkets, Karl gasped in astonishment.

“Is that all you found?” he demanded. “I thought there might have been some gold statues, or the like.”

“If there were we couldn’t locate them,” Joe said. “We considered ourselves lucky in finding what we did. They are worth many hundreds of dollars, maybe thousands.”

“Dad and Mr. Lewis and the others—are they all right?” Bob was anxious to learn if any misfortune had befallen his father and friends.

“They’re still hunting for specimens,” returned the aviator. “Mr. Wallace fell down a mountain and hurt himself slightly, but he’s about all right now. And you should see the large collection of birds and animals they have.”

“We have something that may interest them,” declared Joe, and showed Karl the huge condor, at the same time telling about his narrow escape from death.

“Wow!” Karl exclaimed when the youth had finished. “And Bob and Doc Rander came to your rescue, did they? Good for them.”

It was later decided that Bob and Joe accompany Karl at once in the monoplane to the Comberciato River, where the chums’ fathers were collecting specimens. The old man explained that he did not mind going on alone to Pasaje, where he had business.

“But before you leave,” Dr. Rander began, “I want to divide the treasure with you fellows,” addressing Bob and Joe.

“Don’t give us half,” Joe said pleadingly. “After all, it was your efforts that located the secret mountain cavern.”

The old man held up a hand for silence.

“You forget that I owe my life to you,” he reminded them. “If it had not been for your coming to my rescue, I would not be here to enjoy the treasure.”

“But——” began Joe.

“Say no more,” Dr. Rander silenced him. “Half of the gold is yours.”

He spent the next half-hour in dividing the treasure, giving the boys a good share. They thanked him warmly, then turned to Karl Sutman.

“Can we get started before long?” asked Joe. “I’m anxious to see everybody.”

“Sure.” The aviator was willing. “Let’s get your stuff loaded in the ’plane.”

They worked steadily until noon, at which time everything that belonged to the youths was packed in the supply compartment of the monoplane.

After the meal they bade Dr. Rander an affectionate farewell and stepped into the cabin. Karl started the engine, and then, with a roar and a rush, they started rolling over the field.

The old man waved as they left the ground and headed toward the north. The last the air travelers saw of him he was getting the pack animals ready to finish the journey to Pasaje.

“I suppose we’ve seen the last of him,” remarked Bob, as they left the ground. “We may hear from him later, though. He has our addresses.”

“Rather an odd character, isn’t he?” said Joe. “Seems strange that he’d want to remain in these mountains all his life.”

During the next few hours Karl sent the airplane ahead over mountains that were more rugged than any the youths had ever seen before. He was steering the machine near Mount Panta and the locality in which were Dr. Rust and the other archæologists when suddenly he found himself almost unconsciously entering a heavy cloud.

A second later, when he realized what he had done, the aviator saw that it was too late. Already the ’plane was in the midst of a heavy opaque atmosphere of white.

“I was a nut for getting in a place like this,” Karl said through the telephone. “And there’s no way of getting out now only to go on through it.”

Karl well knew that they were in grave danger of crashing into the side of some lofty peak. They were in a region of tall mountains, and some high summit might easily loom up before them.

For the next few minutes the youths’ hearts were in their mouths. They knew that Karl was an excellent pilot, but they also knew that he could do nothing if sudden tragedy might come upon them.

“What’s that?” cried Bob quickly. He had seen something that looked like a huge black mass directly before them.

Joe sat on the edge of his seat, expecting every moment to feel a terrible crash and then.... For the first time he wondered what death was like.

Cries of relief came from the youths as they saw that instead of crashing into the black mass, they were passing through it.

“As if a million pounds were lifted off my back,” gasped Joe. “I thought we were goners sure.”

“Would be if that were a mountain,” Bob said. “As it is, we’re no worse off than before. It’s a lot darker, though.”

Karl sought to pass out of the cloud by gaining altitude, but he soon saw that this was useless. Still, he thought it best to fly higher. There was a limit to the height he could safely reach, however, for neither himself nor the youths were using oxygen, and the high rare air was not sufficient to supply enough necessary to the human body.

“I’ll have to trust to luck, I guess,” he said through the telephone. “We may make it all right.”

“Karl didn’t say that any too hopefully,” remarked Joe. “Do you suppose he really fears disaster?”

“It seems like it.” Bob was terribly worried. He did not have much hope of getting out unharmed.

Then suddenly the air travelers received a surprise. The cloud that had a few seconds before been so heavy and dense quickly thinned out until it passed from view. Once more the blue sky was visible.

The explorers could hardly believe their eyes. Had they actually emerged from what seemed like certain disaster? It was some time before anyone spoke.

“What do you think of that one?” Karl Sutman’s voice was the first to break the silence. “Couldn’t have been much worse suspense, could there?”

“We didn’t see that we had much chance,” said Joe gravely. “And when we saw that black mass——”

“We’re out of it now, though,” the aviator said. “So why not dismiss it from your mind?”

He was put out to think that the monoplane was several miles off its course, but he refused to let that worry him, since they had had such a miraculous escape.

It did not take long, however, to make up for the lost time, for the young pilot well exceeded the hundred-and-fifty-mile-an-hour cruising speed of the monoplane.

As best he could he kept the machine as near the mountain tops as was safe, so as to make it unnecessary to use oxygen. Getting out the masks and tanks would require much time, and that was what they did not want to spare.

“There’s Mount Panta,” observed Joe, his eyes on a massive peak. “Why can’t we stop and see the archæologists—for only a few minutes, I mean? I suppose they’re still looking for Inca ruins in this region, aren’t they?”

“Yes and no,” laughed Karl. “I mean this: they’re still searching for ruins, all right, but not in this part of the Andes. I stopped to see them just before I flew after you fellows, and they told me they were going to leave for another section over to the east.”

“Wish we could have got in touch with them,” said Bob. “We have information about Inca secrets that would make them jump up and down with joy. Maybe we can tell them later, though.”

A half-hour of flying from Mount Panta brought them within sight of the Comberciato River, along whose banks somewhere the youths’ fathers and Mr. Wallace were staying.

Suddenly Bob and Joe cried out in delight.

“Dad! Mr. Lewis! Mr. Wallace!” said Bob happily.

---

THE joy of Bob and Joe at seeing the naturalists was certainly great. After those strenuous weeks in the mountains, the youths had been growing anxious to be with their fathers and Mr. Wallace again. Now, as they viewed the men waving at them from below they were overly anxious to land.

There was a wide open place directly under them, and to this Karl sent the monoplane. When finally it came to a stop, Bob and Joe dashed out and ran to meet their fathers and the scientist from Chicago.

“Boys!” cried Mr. Holton, too joyful for words.

He and Joe’s father and Mr. Wallace fairly ate the youths up in their happiness at seeing them alive and well.

“You came through all right, I see,” laughed Mr. Lewis, after the first few remarks were over. “What kind of a time did you have? And the treasure—did you find any?”

“Look,” returned Joe and showed them the box of gold beads.

The men cried out in astonishment. Unlike Karl Sutman, they had expected the youths to return without having found anything of value.

“You were successful, all right,” observed Mr. Holton. “Tell us about your adventures.”

While the men listened intently, the boys related their experiences from the time they had left Cuzco with Dr. Rander.

When at last they were finished, the naturalists shook their heads gravely.

“It was all very interesting, but at the same time it was dangerous,” said Bob’s father solemnly. “Afterward we wished you fellows hadn’t gone.”

“But they came through all right—and brought us a white condor at that,” beamed Mr. Lewis. “No doubt this is the only condor real we’ll see. We did shoot two of the more common kind, though.”

“Did you get many specimens?” inquired Bob.

“Come and see for yourselves,” smiled his father and led the way to the naturalists’ camp.

“Great Scott!” cried Joe, surprised at seeing such a vast number of wild animals and birds. “This region must teem with all sorts of animal life.”

“It does,” returned Mr. Wallace. “And that reminds me. We were going out in search of a black ‘spectacled’ bear this afternoon. We’d like to have you go with us, if you will.”

“Will we?” cried Joe. “Does a cat miaow?”

The naturalists had everything in readiness for the bear hunt. They had but to eat a lunch and then they would be ready to start the hunt.

Mr. Lewis had heard reports from natives that one of the huge animals had been seen in a dense woodland beside the river. To this spot the party went, rifles in readiness.

When they entered the jungle they were met with total surprise. Beside an opening in the hillside was the bear, crouching low for a charge!

There was only a moment to act.

“Shoot!” cried Joe fearfully. His rifle had been dashed from his grasp by a protruding tree bough.

Bob had taken a position a number of yards from the others. He had intended to search another part of the jungle. The youth was holding his gun in readiness now, looking for a chance to take aim.

Then he thought the time had come to fire, and pulled the trigger.

Bang! The rifle spoke, but the bear had suddenly turned, and the bullet missed.

With a snort of rage the huge beast turned on Bob, showing its terrible teeth savagely.

Bob saw the danger and was hurriedly trying to work the bolt on his rifle. But unfortunately the mechanism had jammed.

Helpless, the youth would be at the mercy of those terrible teeth and claws! Already he could imagine the horror of what would follow.

Bang! Bang! Two rifles barked, and each bullet found its mark. Another shot and the huge bear fell dead, almost at Bob’s feet.

“Whew!” gasped Karl Sutman, holding his smoking rifle. “Another narrow escape to add to you fellows’ already long list.”

“We’re piling ’em up thick and fast,” said Bob. He could laugh, now that the danger was over.

They made their way back to camp, after having cut off the great skin. It was at once placed in preservative.

“One more prize specimen to add to our collection,” said Mr. Wallace. “I’m betting that Bob and Joe will prove a valuable asset to the expedition during the next few weeks. They’re both good shots, and they have plenty of courage.”

Indeed the youths tried to justify themselves of this tribute, and were successful in doing so. During the eventful days that followed they collected many specimens for the scientists, including about every form of life they could see in this wild region. Often they made long excursions into the adjoining mountains in search of new wild creatures, and usually found them. Taking moving pictures also occupied their time.

But although the naturalist party was meeting with success in its search for fauna, the men did not wish to remain here too long, for other duties at home prevented it. Especially was Mr. Wallace anxious to get back to Chicago.

It was arranged one day that he and Bob and Joe go with Karl Sutman in the monoplane back to the United States, preceding Mr. Holton and Mr. Lewis, who would arrive later by steamship. The youths’ fathers took it on themselves to attend to getting the specimens on muleback to the coast, where they would be loaded on the vessel.

The four leavetakers were given an affectionate farewell by Mr. Holton and Mr. Lewis, who expressed hope that their sons and friends would arrive in the United States without mishap.

On the way to the coast the air travelers stopped to see Dr. Rust and others of the archæologist party. Bob informed them of the Inca secrets he and his friend had found, and gave them the map he had made of the region. The scientists’ delight far exceeded the boys’ expectations. They literally mauled the youths in their intense enthusiasm.

When the chums, Mr. Wallace, and Karl climbed into the cabin, the scientists gave them a royal send-off, wishing them a safe journey.

And safe it proved to be. Karl’s ability as a pilot was greatly appreciated as they flew toward the United States, which they reached without incident.

“Now to get home,” said Bob, as he and Joe and Mr. Wallace hailed a taxi. The naturalist intended to spend another day or so with the boys before boarding a train to Chicago. Karl Sutman left them at the airport, promising to get in touch with them within the next few days.

At their homes Bob and Joe and their friend were given a profound welcome by Mrs. Holton and Mrs. Lewis, who were desirous of knowing about their experience.

“We had a wonderful time,” said Joe, as they all sat in the Lewis living room. “And we met with adventures aplenty. There’s nothing quite like exploration, especially when you’re looking for ancient secrets.”