AT Dr. Kirshner’s dread explanation, Joe cried out in surprise and fear.

“Captured!” he mumbled in a strange voice. “Find out how long they are going to keep us.”

The scientist put the question before the Arabs, who laughed mockingly.

“Until the treasures have all been taken from the hidden cave,” they replied in the native language.

Dr. Kirshner could hardly believe his ears.

“Then—the riches have been found?” he demanded.

“Yes. And we are to keep you away. We know not how long it will be. If you act right, we will treat you well. But if you try to get away you will be severely punished.”

“Where are you taking us?”

For answer the Arabs only laughed.

“What do you think of it?” asked Joe, after his friend had translated the natives’ words.

Dr. Kirshner shook his head.

“Looks like we’re not going to get back to camp today,” he said gravely. “Worst thing is, these rascals may hunt out our friends and capture them also. If we could just leave some word that would give them a hint to be on the lookout——”

The two Americans were forced along the narrow edge of a deep canyon, and more than once they felt that they were but an inch from death. Their tempers were thoroughly aroused, but they knew that they had no chance against such a horde.

“These fellows are a bit different from American roughnecks,” Dr. Kirshner said. “Arabs would not hesitate to stick a knife through you if not satisfied with your actions, but our own countrymen would ordinarily think twice before doing such a thing.”

The two explorers were in the midst of the group, with swarthy natives on each side of them. To attempt to break loose would indeed be futile.

“I wonder if we will be taken near the hidden riches?” muttered Joe, gazing ahead at the distant country.

“Hard telling,” the archÆologist replied. “Of course it is possible, but I doubt it. Still they might purposefully show us the treasure to let us know how much we are missing.”

A half-hour’s traveling brought them to the base of an unusually high peak. It might, thought the Americans, be Mount Oudane or Illiman, as it was every inch of ten thousand feet.

There was a small well in a crevice between the rocks, and much to their great delight the prisoners were given the opportunity to drink to their hearts’ content. The water was unusually cool, protected as it was from the heat of the sun.

But only a few minutes’ rest was allowed, even though the Americans were very tired after the ceaseless afternoon tramp.

Another hour of hiking over the rough country brought them to a high hill, which Dr. Kirshner said led to the central plateau of Atakor. For a great distance it was almost flat country, with little or no vegetation.

The prisoners were forced to climb a narrow ledge and came at last to the top of the mountain. To their right was a large entrance that led undoubtedly into a cave.

The Arabs motioned for the whites to stop and turn into the cavern. Dr. Kirshner and Joe hesitated for a moment then did as directed.

At first they found themselves in utter darkness. As their eyes became more accustomed to the blackness, they saw that a long, narrow tunnel stretched away from the back of the cave. Whether it led to any place in particular they did not know.

“Well, I guess we’ve come to the end of our tramp,” observed Joe, looking about to see what the Arabs intended to do next.

There were no chairs or boxes to sit on, but slabs of rock invited the newcomers to sit down.

As soon as it became evident that the Americans had settled themselves, the Arabs stationed themselves at the entrance of the cave. Before long, however, all of the men but three departed.

“Looks bad for us,” remarked Dr. Kirshner. “We were fools to start out alone in this country when we knew we were getting near the hidden riches.”

“Too late now,” mourned Joe. “We’ll have to make the best of it, I guess. But I’d feel a lot better if we had some way to warn Dad and Bob and the others. Perhaps they’ll walk right into a trap set by those Arabs.”

The cave in which they were guarded was in the side of a wall of rock, which was several hundred feet above the surrounding mountains. From their lofty positions the Americans could look out over scores of miles of rugged country.

Dr. Kirshner had his binoculars strapped over his shoulder and took them out to view the distant panorama. The binoculars were of very high power, made by a well-known firm.

Suddenly his eyes fell on something that made him gasp in astonishment.

“The cave of riches!” he cried. “I can see it! And there are five or six Arabs walking inside!”