All of them were very tired after that long day's traveling, and, since no danger could come upon them out on the arid waste, sentries were dispensed with. Dick sat up longer than the rest, thinking he ought to keep an eye on the dusky guide; but the Indian appeared to be soundly sleeping, and weariness finally compelled the boy to succumb. The morning came and brought with it a very disagreeable surprise. At some time during the night the sorely tempted Indian guide, forgetting his obligations to Captain Lewis, had taken an extra horse they had along and started on the back trail; not only that, but he had also carried off considerable of their supply of water, leaving the adventurers face to face with a terrible calamity. CHAPTER XXV THE OASIS "I'M sorry now I allowed myself to go to sleep at all," said Dick, as he heard what had happened. This was the first Roger knew of his suspicions, for Dick had felt that it was hardly worth while taking his chum into his confidence. "Do you mean you didn't like the way that Indian acted, and that you meant to stay awake to keep an eye on him?" demanded Roger. "I did at first, but I was very tired, and he seemed to be sound asleep; so I gave it up. Perhaps, if I had kept awake for just another half hour, I might have caught him in the act." All of them were feeling depressed over the incident. It was not so much the horse they regretted, though the animal might prove valuable to them later on; but having their supply of drinking water cut short told heavily. They started on with heavy hearts, and the future looked dismal, indeed. Still, it was not the nature of such a man as Captain Lewis to despair when, after all, there might be no occasion for trouble. His good nature presently infected the remainder of the party, and hope again found lodgment in their hearts. By being careful, the water could easily be made to cover two days, and by that time it was believed they would have found a fresh supply. It had been only recently that the two boys had learned certain facts that gave them considerable cause for worry. One of the trappers, who had been out hunting just before the caravan reached the foot of the mountains, had discovered two men who wore the garb of whites. They were armed with guns and had horses in the bargain. He had not been able to creep close enough to hear anything they said, but, from the description which he gave of the strangers, both Dick and Roger felt sure they knew who they must be. The one with the black hair and beard was the vindictive French trader, François Lascelles; while his companion could be no other than the treacherous Andrew Waller, who had been kicked out of the camp when his duplicity became known. The two rascals had evidently joined forces, and continued to follow after the explorers, bent on having a sweet revenge for the indignities that had been visited upon their heads, though rightly, by Captain Lewis.