As soon as the low-lying ground was traversed, the journey became heavy. Often the travellers were more than ankle-deep in the hot sand, while, as they came to the slope of the hill, they frequently found that their feet slipped back more than they gained. But by dint of great exertion they reached the summit of the hill. Here the three stood spellbound. Beyond, the desert extended unbrokenly for nearly a mile, then the ground rose abruptly to a height of about four hundred feet. The summit of this hill was clothed in verdure, while above the tops of palms appeared the battlemented walls and towers of a large town. Some of the latter were flat-topped, while others were capped by conical roofs of bright metal that glittered in the sunlight. From the topmost turret floated a banner, but the distance was too great for the spectators to discern its device. "Hurrah!" shouted Hugh. "We're saved. But what a strange sort of town to tumble against in the midst of the desert!" "It looks more like a city in the fairy-tale books," said Gerald. "Let's push on at once." "Steady, lads!" exclaimed Reeves. The man spoke as if lost in thought. "It may be that---- Ah!" Even as he spoke, the hill upon which the city stood appeared to be riven asunder. The walls and turrets oscillated as if shaken by an earthquake; then, as if wiped out by a titanic hand, the vision vanished, leaving only the trackless desert shimmering in the rays of the powerful sun. "A mirage!" exclaimed the three simultaneously; then dismay once more overtook them, as they saw only the pitiless waste in front of them. "Surely there must be a real town over there!" exclaimed Gerald at length, pointing in the direction of the vanished scene. "Of that I have no doubt," replied Reeves. "A mirage is the reflection of a real object, but that object may be ten miles away, or it may be a hundred--or more. That sort of thing has often lured men to death." The lads did not reply. Hugh was looking steadily at a point on the distant horizon. "What's up, Rags?" asked Gerald. "I believe I can see palm trees. There--more to your right. You are pointing straight at the place." "So do I," assented Gerald, with no uncertain voice; then, as an afterthought, he added: "I hope it isn't a mirage as well!" "What did you say?" asked Reeves, who was standing a short distance away. "We can see palms." "I believe you are right," was the response, "only I cannot be sure of it." "Gerald suggested that it might be a mirage. If not, it's a clump of palms, right enough." "We've had disappointments enough for one day," replied Reeves decisively. He had shaken off his meditative mood, and was now alert and resourceful. "We'll go back now and rest till to-morrow. At dawn we'll come here again, and if in the clear morning light the trees are still visible, we will then know that it is not a mirage. In that case we'll make a dash for it."