They were now rapidly leaving the region of low sand dunes behind. Rocks of all sizes and shapes became more numerous, and vegetation was more abundant. There were, however, stretches of coarse sand plains, which were now and then dotted with boulders. Suddenly, as they ascended a long low hill, Bob and Joe cried out in delight and pointed to something a half-mile or so away. "A lake!" exclaimed Joe happily. "A lake of water!" CHAPTER XIX Searching for the Ancient "Not a lake," said Fekmah, shaking his head. "Only another mirage. They are rather common all through this region, and we may see much more short time." "Well, if there was a real lake there beside that mirage, I wouldn't know which to pick," confessed Joe. "And look! Even waves are there. And foam caps!" "Wonderful facsimile, all right," remarked Dr. Kirshner. "Old Nature is capable of playing mighty big jokes on us sometimes." For over a half-hour the illusion was visible to the explorers; then, when they rounded a large pile of rocks, it could no longer be seen. "And I'm glad," said Bob. "Now maybe I can get my mind away from thinking only of water. It wasn't very pleasant to see what looked like it and not be able to have it." "When do we come to another oasis?" inquired Joe of Fekmah. "Tishmak say within next fifty miles," was the response. "It be very small, but there be much water to drink." Late that evening they came to the foothills of the Ahaggars. Majestic Mount Oudane was directly before them, and the whole Ahaggar range appeared to be only a few miles away in the clear desert air. They at last reached the small oasis among the many red boulders. After filling their containers, they continued toward the mountains, greatly refreshed and ready for action. But darkness was rapidly falling, and it would be necessary to stop before long for the night. Tishmak, however, thought it best to travel in the moonlight. The others were more than willing to do this, for now that they were so near their goal they hesitated to lose any precious time. "We can go on for a while," said Mr. Lewis, as daylight rapidly faded. "Then we'll turn in and get a few hours of sleep." Soon it became dark, making it necessary to stop. But before long the moon came out in full splendor, flooding the rocky vastness with enchanting light. The distant needle-like peaks took on a strange appearance, like mysterious towers of a fairyland. The scene was unusual and slightly weird, resembling the rough surface of the moon. For some time the Americans were silent, absorbed in thought. Finally Bob roused himself. "Those mountains seem rather intangible, or ghost-like," he remarked, as he and Joe rode at the rear of the caravan. Joe nodded. "It's like we're the characters of an Arabian Nights story," he muttered. "No vegetation, no life of any kind around anywhere. Gets under my skin a little."