The oasis was about forty miles away, situated on a barren sand plain surrounded by mountains. The Tuareg explained that there was no other well near and that the prisoners would be forced to stay there for an indefinite period, for no caravans passed along that way. In order to get to the place it was necessary to go through the mountains, and traveling was not any too easy. But they rode with a determination and finally arrived at the oasis. The Arabs were commanded to dismount and walk forward. Then, after filling their canteens with water, the Americans and the Tuaregs started the return journey, herding the dromedaries ahead of them. "Now that that's over, maybe we can rest easy," said Dr. Kirshner. "Those Arabs can't get away because of not having camels, and the monotony will punish them greatly." Bob, the scientist, and the Tuareg made good time that afternoon, arriving at the explorers' camp just before sundown. The chieftain lost no time in getting back to his village, after being thanked warmly for his services. "We'll see that those Tuaregs get a reward," said Mr. Holton. "Just as soon as we get to the hidden treasure we'll give it to them." The natives had not been told of the cave of riches, however, for fear that their age-old desire to raid might get the better of them. Very early the next morning the explorers got their belongings placed on the dromedaries and started out for the cave of treasure. Although it would mean only a few hours' journey, they were extremely impatient. "Wonder if those Arabs carried any of the riches away?" asked Bob, as they rode toward the high wall of rock, in the side of which was the cave. "No," Mr. Holton returned. "They hadn't started yet. Were just looking over everything. At least that's what our guards told us. It seemed that they intended to carry the stuff out in a day or two." "Wanted to catalog everything first, huh?" asked Bob. "Well, it's a good thing we stopped them when we did." Fekmah found it necessary to consult his duplicate map very frequently, and he wondered if he had remembered to put in all the details accurately. Finally, after they had passed the tall wall of rock and were following a narrow trail up the mountain on the opposite side of the cliff, Dr. Kirshner turned to Bob. "You asked the other day how we were to get into the cave," he said. "Of course it would be impossible to scale that lofty cliff. Fekmah's map points out a narrow opening in the rock somewhere in this vicinity, and we ought to find it in a very few minutes now." He had scarcely uttered the words when Fekmah cried out in delight and pointed to a peculiar rock formation not far ahead. "There it is," he declared joyfully. "There is where we enter mountain to get cave of treasure." The explorers, led by Fekmah, moved on up to the spot. "Here's an opening!" cried Joe, pointing to a small crack that was barely large enough to let them in.