The roar of the canyon had been in his ears so long that it seemed like silence, and it had lulled him to sleep hours before. He was still suffering from hunger and longed for the return of his captor, for he thought he would bring food with him. Providentially the lad had stood in this position but a short time when he looked aloft toward the sky. At the moment of doing so he uttered an exclamation of affright and leaped back into the mouth of the cavern. The next instant a boulder that must have weighed a ton crashed upon the ledge where he had been standing, splintered off a number of pieces, and plunged into the torrent below. Fred did not try to make himself believe that the falling of this mass of stone was an accident. Motoza or one of his allies had been on the watch above for the appearance of the youth, and when the boulder had been adjusted as well as possible it was tumbled over into the canyon. Had Fred remained on the spot a few moments longer he would have been crushed like an insect under the wheel of a steam-engine. It was a startling occurrence, and in his weakened condition made him so faint that he withdrew still further into the cavern and sat down, trembling like a leaf. His hunger had vanished and hope almost departed. "It will not do for me to leave the cavern in the daytime, for he is waiting for me to do so. I can't do it at night without some one to guide me. He means to keep me here until I die of starvation." Fred had come really to believe this. He knew enough of Indian nature to understand that the race rarely inflict instant death upon an enemy when it is in their power to subject him to torture or slay in some horrible fashion. Motoza had not slain him before because he was unwilling that the one whom he hated so intensely should receive such mercy. It would be a hundredfold sweeter to the Sioux to see his prisoner dying by inches. "If he has a plan for making father pay a ransom for me it will take a number of days to bring the thing to an end. During all that time I am to be left without a morsel of food; he would deprive me of water, too, if he could." It was a shocking conclusion to form, but the usually clear-headed boy became convinced he was right. "Poor Jack must be worried almost to death," he murmured, sitting on the stones and giving rein to his fancies; "he will know that something has gone wrong with me, but he can never know what it was. Hank will lay it to Motoza, for he has said there is nothing too wicked for him to do, but the cowman has no way of finding what has become of me, and he can't make Motoza tell him. He and Jack may hunt for weeks without suspecting where I am." In this declaration Fred Greenwood, as is known, was not quite correct, though the search of his friends was fruitless. CHAPTER XX. A CLIMB FOR LIBERTY.