He had been walking but a short time when he abruptly halted, under the impression that he had seen an Indian run across the gorge directly in front of him.  This caused a wilder throbbing of his heart, and another examination of his gun, which was loaded, as he had assured himself some time before, and ready at any time to do him one good turn, if no more.

“He wouldn’t have skipped over in that style if he had known I was so near,” was the reflection of the boy, as he sheltered himself in the shadow of the rocks and looked and listened.  “How did he know but what I might have picked him off?  What was to hinder me?  If he did n’t know I was here, why, it ain’t likely that he would loaf along the side of the ravine.”

By such a course of reasoning, he was not long in convincing himself that the way was open for his advance.  He hurried by on tiptoe, and drew a long breath of relief when certain that he had passed the dangerous spot.  But he was only a short distance beyond when his hair fairly arose on end, for he became certain that he heard the groan of a man among the boulders over his head.

“I wonder what the matter is there?” he whispered, peering upward in the gloom and shadow.  “It may be some white man that the Indians have left for dead, and that still has some life in his body, or it may be an Indian himself who has met with an accident—­helloa!”—­

Just then it sounded again, and a cold shiver of terror crept over him from head to foot, as he was able to locate the precise point from which it came.  The frightful groaning did not stop as suddenly as before, but rose and sank, with a sound like the wail of some suffering human being.

As Fred stood trembling and listening, his shuddering fear collapsed; for the sound which had transfixed him with such dread, he now recognized as the whistling of the wind, which, slight in itself, was still manipulated in some peculiar fashion by a nook in the rocks overhead.

“That does sound odd enough to scare a person,” he muttered, as he resumed his walk.  “It must be a regular trumpet-blast when the wind is high, for there isn’t much now.”

The two incidents resulting so harmlessly, Fred was inspired with greater confidence, and advanced at a more rapid walk along the ravine, suffering no check until he had gone fully a mile further.  Just then, while striding along with increasing courage, he came to a place where the side of the ravine was perpendicular for two or three hundred feet.

He was close to this, so as to use the protection of the shadow, and was dreaming of no danger, when a rattling of gravel and debris caused him to look up, and he saw an immense mass of rock, that had become loosened in some way, descending straight for his head.

CHAPTER XIX THE MYSTERIOUS PURSUER

Young Munson made a sudden bound outward, and, just as he did so, a mass of rock weighing fully a dozen tons, fell upon the precise spot where he had stood, missing him so narrowly that the blast of wind, or rather concussion of the air, was plainly felt.  The boulder broke into several pieces, its momentum being so terrific that the ground for several feet around was jarred as if by an earthquake.