This was rather vague theorizing, however. Look and stare as much as he chose, he could detect nothing that resembled man or animal. He shrank to one side and waited several minutes, in the hope that the thing would explain itself. But it did not, and, after waiting some time, he resumed his journey along the ravine, keeping close to the shadow on the right side, and using eyes and ears to guard against the insidious approach of any kind of foe. Sometimes, under such circumstances, when a sound has very nearly or quite died out In the stillness, there seems to come a peculiar eddy or turn of wind, or that which causes the sound, passes for an instant at a point which is so situated as to impel the waves of air directly to the ear of the listener. Fred did not exactly understand how this thing could happen, but he had known of something of the kind, and he was gradually bringing himself to explain the thing in that fashion, when his theory was upset by such a sudden, violent rattling of hoofs, so close behind him, that he leaped to one side, fearful of being trampled upon. “That's a pretty way to come upon a fellow!” he gasped, whirling about with the purpose of shooting the red-skin for his startling introduction. But neither rider nor horseman was visible. The watcher could scarcely believe the evidence of his own senses. It seemed to him that the Apache, as he believed him to be, must have turned abruptly aside, into some opening in the side of the ravine, but he could not remember having seen any place that would admit of such strategy. When he came to reflect upon it, it seemed impossible. “Well, that beats everything,” he said, with a perplexed sigh. “That sounded so close that I expected to be run over before I could get out of the way, and now he's gone.” He waited some minutes, and, hearing and seeing nothing, once more resumed his stealthy way along the gorge, a new, shivering fear gradually creeping over him, as it does over anyone who suspects himself in the presence of the unexplainable and unnatural. “I wonder whether they have ghosts in this part of the world?” he said to himself. “I used to hear the men talk of such things, but father said there was nothing in them, and so I didn't believe them--but I don't know what father would say or think if he was in my place.” There was the strong counter-belief, also--the conviction that most likely there was a reality about the thing--which kept Fred on the _qui vive_. He was determined, if possible, to prevent a repetition of the startling surprise of a few minutes before. He scrutinized the side of the ravine as he walked along, on the lookout for any opening or crevice which would permit a man and a horse to find shelter. It did not seem possible that any retreat that would shelter them could escape the eyes of the lad. “I haven't seen any such place yet, so, if the Indian is trying any such trick, he can't do it here without my seeing him, and if I do--Heaven save me!”