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!”