“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.