Being left entirely to himself, the boy now devoted himself to the somewhat dismal task of keeping watch, an occupation that cannot be classed as the most cheerful in which a man may engage. The excitement and apprehension that marked the first two or three hours prevented the time from hanging too heavily upon his hands, but as the night stole along and nothing was heard or seen to cause alarm, the fear grew less and less, until, like a boy, he began to suspect that all these precautions were useless. For the twentieth time he stood up and listened. The soft, musical murmur of the Rio Pecos was heard, as it flowed by on his right, and now and then the gentlest possible breath of night-wind disturbed the branches overhead; but nothing else caught his notice. To prevent the feeling of utter loneliness from gaining possession of him, Fred occasionally emitted a low, soft, tremulous whistle, which was instantly responded to from the direction of Mickey. It was the old familiar signal which they had used many a time when off on their little hunting expeditions, and either, hearing it, could not mistake its source. But this grew wearisome at last, and he leaned back against a tree, looking out upon the moonlit valley beyond, where nothing as yet had caught his eye that looked in the least suspicious, and where everything still appeared as silent as a graveyard. “I don't believe there are any Indians within fifty miles,” he muttered, impatiently; “and yet we must have three or four men on the look-out till morning. Well, I s'pose it's the only safe thing to do, and I'm bound to stick it out till one o'clock. It must be near midnight now, and if Mickey should come around here, an hour from now, and find me asleep, I never would hear the last of it.” He felt very much like sitting down upon the ground, but he knew if he did that he would be sure to fall asleep, while, as long as he kept his feet, he was sure to retain his senses. When disposed to become too drowsy, a sudden giving away at the knees recalled him so vigorously, that it was a considerable time before the drowsiness crept over him again. Thus the night advanced, until all at once, Fred aroused himself as if a sharp pin had been thrust in him. “By George! I heard something then!” he exclaimed, in an excited undertone, looking sharply about him; “but I don't know where it came from.” His impression was that it came from some point directly before him out on the open space; but the most rigid scrutiny failed to reveal the cause. There was the level stretch of grass, unbroken by stone or shrub, but nothing that could be tortured into the remotest resemblance to a human figure. “It can't be there,” he muttered; “or if it was, it do n't amount--” His senses were aroused to the highest pitch, and he was all attention.