But when, wholly unable to explain or to credit it, he turned his attention to the other tracks to discover if they, too, bore similar witness, he noticed that these had meanwhile undergone a change that was infinitely worse, and charged with far more horrible suggestion.  For, in the last hundred yards or so, he saw that they had grown gradually into the semblance of the parent tread.  Imperceptibly the change had come about, yet unmistakably.  It was hard to see where the change first began.  The result, however, was beyond question.  Smaller, neater, more cleanly modeled, they formed now an exact and careful duplicate of the larger tracks beside them.  The feet that produced them had, therefore, also changed.  And something in his mind reared up with loathing and with terror as he saw it.

Simpson, for the first time, hesitated; then, ashamed of his alarm and indecision, took a few hurried steps ahead; the next instant stopped dead in his tracks.  Immediately in front of him all signs of the trail ceased; both tracks came to an abrupt end.  On all sides, for a hundred yards and more, he searched in vain for the least indication of their continuance.  There was—­nothing.

The trees were very thick just there, big trees all of them, spruce, cedar, hemlock; there was no underbrush.  He stood, looking about him, all distraught; bereft of any power of judgment.  Then he set to work to search again, and again, and yet again, but always with the same result:  nothing.  The feet that printed the surface of the snow thus far had now, apparently, left the ground!

And it was in that moment of distress and confusion that the whip of terror laid its most nicely calculated lash about his heart.  It dropped with deadly effect upon the sorest spot of all, completely unnerving him.  He had been secretly dreading all the time that it would come—­and come it did.

Far overhead, muted by great height and distance, strangely thinned and wailing, he heard the crying voice of Defago, the guide.

The sound dropped upon him out of that still, wintry sky with an effect of dismay and terror unsurpassed.  The rifle fell to his feet.  He stood motionless an instant, listening as it were with his whole body, then staggered back against the nearest tree for support, disorganized hopelessly in mind and spirit.  To him, in that moment, it seemed the most shattering and dislocating experience he had ever known, so that his heart emptied itself of all feeling whatsoever as by a sudden draught.

“Oh! oh!  This fiery height!  Oh, my feet of fire!  My burning feet of fire ...!” ran in far, beseeching accents of indescribable appeal this voice of anguish down the sky.  Once it called—­then silence through all the listening wilderness of trees.