"It is strange how that tool got on the surface of the ground," he remarked, as they turned the dromedaries ahead. "Other expeditions have penetrated into this region, and it is quite obvious that they would have found it had it been in sight." "Perhaps a rainstorm washed it out of the ground," suggested Mr. Holton. They rode until late that night, for they were anxious to come to the gorge of Arak some time the next day. "We should see it tomorrow afternoon," predicted Fekmah. Notwithstanding this, they rode all the next morning without coming to the landmark. Finally Tishmak gave up in disgust and stopped in the shade of an overhanging rock. It was nearly noon, and the necessity to get a meal was becoming more apparent. When they had finished eating they continued to rest in the tent. At this high altitude the sun was less hot than it had been on the plateaux, and it would have been possible to ride farther. But they had become accustomed to the usual afternoon rest and were loath to depart from this regularity. But Dr. Kirshner had sat only a few minutes before he got up and stretched. Mr. Holton and Mr. Lewis were asleep, but Fekmah and Tishmak remained awake. Bob and Joe sat in one corner of the tent, sleepily gazing out at the distant peaks. "I'm going out and look around," Dr. Kirshner said to them. "Care to go along?" Bob replied in the negative, but Joe arose and walked over to his rifle. "Don't stay too long," advised Bob, as Joe and the archæologist started out. They were familiar with the country in the immediate vicinity of camp. As there was nothing of new interest to be found there, they hiked farther to the south. The scientist wished particularly to find more ancient inscriptions, and, if possible, other evidences of ancient civilizations. "What's this?" cried Joe, slapping his hand to his face. "Well I'll be---- Some kind of a fly." "It is a wonder we haven't come across insect pests long before this," Dr. Kirshner said. "They are very common all through this section." The flies had been discovered while they were trudging through a long, hot passageway between two high wall-like rocks. Now, as the two adventurers passed farther on, they came into more of the insects, which swarmed about as if thirsty for human blood. "Ought to have some kind of a spray," remarked Joe, pushing them away in great numbers. "We have, in camp," his friend said. "If the pests bother us much we'll have to make use of it." After an hour's hike they came to another dry river bed, and again Dr. Kirshner found flint implements scattered about. Joe had a small motion-picture camera with him, and at the scientist's request he filmed the half-buried primitive tools as they lay hardly visible in the sand. "I want proof that these antiquities came from the Sahara," Dr. Kirshner said, placing them in the small box he carried over his shoulder for the purpose.