He was in a peculiar humor. Like the dog who did not want the bone, he was angry at any other dog getting it, and so Max, while he would not marry Girzilla, was furious and jealous at the thought of Ibrahim claiming her as his wife. Sherif el Habib walked back to the camp, and orders were given to follow the course of the stream. For four hours the march was continued through the long grass. It was almost as wearisome as journeying across the sand. After two hours journey on the next day, a quagmire prevented them from following the stream, and they had to make a detour to the right. The river was kept in sight, however, and for two days it could be seen flowing briskly along toward the realm of illimitable sand. “Where is the river?” asked Max. The mystery increased. The river seemed to end abruptly in a sand bank. It was true. All vegetation ceased; the oasis had been crossed. The green grass was to give way to dry sand. That did not surprise them. They expected it, but what puzzled them was that a little stream, rising from springs at one end of the rectangular oasis, had swollen into a river, whose rippling waves showed a strong current, and when some great lake was expected, or another river, of which it might be tributary, nothing was found but sand. “It was all a mirage,” suggested Max. “What do you mean?” “Why, we only imagined the river.” “You are a fool!” angrily exclaimed Ibrahim. “Thank you; we are brothers,” retorted Max. Ibrahim laughed, and acknowledged that Max had the best of it. “Seriously, though, there was a river and the water must empty itself somewhere.” “Of course.” “Well, where does it go to?” “To the place where it empties itself,” answered Max. “Confound you, Max! be serious. Who knows but that we are on the verge of a great discovery?” “Yes; and that we may be heralded all over the world as the mighty explorers who found the river Ibrahim, which had its rise in an atom of sand, and flowed into the lake of nothing.” Then, pausing, he suddenly slapped Ibrahim on the shoulder. “Say, wouldn’t we make money as lecturers? You should go as the great Persian pasha, warranted genuine; while I would introduce you----” “Boys, there is a mystery here,” said Sherif el Habib, coming up at the time; “and if I were your age----” “So you are, pasha,” said Max. “Yes, my boy, and older. But if I were young I would find a way to solve the mystery.” “May we try it?” “Yes; and may Allah and the Prophet guide you.” “But what says Girzilla?” asked Max. “She is willing,” responded Sherif, solemnly. CHAPTER XIII. DANGEROUS JESTS. Sherif el Habib, having chosen a camping ground in the oasis, and being supplied with provisions enough for several months, agreed to wait for the return of the young explorers. No sooner were Max and Ibrahim away from the camp than they felt like boys. They were their own masters, and not only that, but they had two Arabs with them as stewards and porters.