Sharply at three o'clock Dr. Kirshner was up stretching himself and suggesting that they continue the journey. "It isn't the thing to wait too long," he reminded his friends, "even if we are drowsy. By night we want to have covered another hundred miles or more. I'm especially anxious to reach the mountainous region and see what I can find in the way of records of ancient peoples who might have lived there before the desert became a desert," he added, laughing. The others were more than willing to start on. When sleepiness or drowsiness threatened to overpower them at the wrong time, the thought of the two thieves who had stolen Fekmah's map spurred them on to action. "I don't know that it is necessary to set a guard while we take our afternoon rests," remarked Fekmah casually, as they packed the tent back in its place for the journey. The Americans looked at him wonderingly. "The dromedaries will give us warning," he explained. "They are much uneasy if stranger come near camp. They jump up and make noise." "A bit like watchdogs, are they?" said Mr. Holton. "Well, we'll give them a tryout the next time." They again took up the journey, winding in and out among the rolling sand hills. Occasionally they would come to a dune several hundred feet high. They seemed to be gradually mounting higher, for the camels did not move as rapidly as before. Vegetation increased still more, giving the dromedaries an opportunity to nibble often on the various plants and shrubs. A few scattered trees began to be seen, their sharp thorns protruding threateningly. "Camels don't bother with thorns," remarked Bob. "They know just where to take a mouthful without cutting their mouths." "And they aren't particular about their diet, either," Joe added, remembering what Fekmah had told him some time before. "Leather, paper, wood--almost anything will satisfy their appetites." At last they came to the region of high sand dunes that were visible the day before. Many of the hills towered five and six hundred feet, and a few were much higher than that. The explorers were lucky in finding a narrow lane that passed between the mounds. How long the good fortune would continue, they did not know. "Getting to look more like the dunes in Indiana, back in the United States," remarked Joe. "But of course these stretch a hundred times as far." In some places the ground was hard and brittle, while in others it was strewn with loose sand. At last the lane stopped, and the adventurers found themselves face to face with a high hill. "Guess we'll have to climb it," said Mr. Holton, looking about. "There is no other way out. The sand seems to be hard and safe enough. And it could be a great deal steeper." "Let dromedaries go slowly," cautioned Fekmah. "Do not hurry them." They began the dangerous ascent, keeping their eyes glued to the ground. Slowly the camels trudged up, feeling their steps carefully.