"I guess most of the rocks here are red," remarked Bob, who had studied books on the Sahara. "Burned that color by the sun, huh?" "Seems reasonable, doesn't it? Come to think of it, though, the ground in the Land of Thirst is black." "The Land of Thirst?" "Yes. I heard Fekmah talking about it this morning. It's a region where there are few or no wells, and you have to be very careful to have a good supply of water in the tanks before you plunge into it." "Looks like even then it would be dangerous. What if a storm or something would hold you back for a long time?" "Have to take that chance," Bob replied. "Wouldn't doubt that quite a few caravans come to a tragic end there." "Will we go through it?" Joe asked. "Fekmah said we might," was the response. Finally they came to the well that Mr. Holton had told about. There was a steady flow of water, which was comparatively cool. "Drink all you want," said Dr. Kirshner. "Tishmak says we won't see another for a long time." The explorers drank and drank, until they could hold no more. Then they began the task of replenishing the tanks. But as little had been taken out, this was finished in a very few minutes. "Now let's get on," urged Mr. Lewis. "We want to cover a good many more miles yet before we stop for the noon meal." Another hour brought them again to a region of hard soil, and the dromedaries increased their pace several miles per hour. "Wish it would stay like this all the way," said Joe, noting that ground was being covered much faster. "Won't though. But we'll have stretches of it here and there." As the minutes passed, the glare from the sand became more intense, and the temperature went steadily up. The boys had dark-colored glasses but hesitated to put them on so soon. "Wouldn't a good cold drink come in fine now?" asked Bob, keeping his hands off his canteen with difficulty. "Sure would. But we must fight the temptation to drink too often," returned Joe. "Remember, we're on the desert now, and not in the mountains, where there are plenty of springs." They rode rapidly on, the country remaining about the same. The red pebbles, however, grew more numerous, some of them glowing like rubies. Joe remarked that they were gradually ascending, and Bob nodded. "There's a line of high dunes over there," he said, pointing to the distant horizon. "Fekmah said when we reach those we'll have climbed a good many hundred feet. We should get to them tomorrow." In a short time they passed beyond the stretch of hard soil and again plodded through loose sand. From all indications, it was heated to a high degree by the fierce sun. How the dromedaries stood it was a mystery to the boys. "I wonder how Tishmak can find the way to the Ahaggar Mountains?" mused Joe, glancing up ahead at the guide. "He isn't using a compass."