It must have been two hours later when they ventured forth.  Silence and loneliness brooded everywhere, not so much as a breath of air stirring the leaves.  The unspeakable, unsolvable mystery of it all rested like a weight on the spirits of both men.  It, was a disquieting thought that bands of savages, eager to discover and slay, were stealing among the shadows of those trackless plains, and that they must literally feel their uncertain way through the cordon, every sound an alarm, every advancing step a fresh peril.  They crossed the swift, deep stream, and emerged dripping, chilled to the marrow by the icy water.  Then they swung stiffly into the wet saddles, and plunged, with almost reckless abandon, through the darkness.  Murphy continued to lead, the light tread of his horse barely audible, Hampton pressing closely behind, revolver in hand, the two pack-horses trailing in the rear.  Hampton had no confidence in his sullen, treacherous companion; he looked for early trouble, yet he had little fear regarding any attempt at escape now.  Murphy was a plainsman, and would realize the horror of being alone, unarmed, and without food on those demon-haunted prairies.  Besides, the silent man behind was astride the better animal.

Midnight, and they pulled up amid the deeper gloom of a great, overhanging bluff, having numerous trees near its summit.  There was the glow of a distant fire upon their left, which reddened the sky, and reflected oddly on the edges of a vast cloud-mass rolling up threateningly from the west.  Neither knew definitely where they were, although Murphy guessed the narrow stream they had just forded might be the upper waters of the Tongue.  Their horses stood with heads hanging wearily down, their sides rising and falling; and Hampton, rolling stiffly from the saddle, hastily loosened his girth.

“They ’ll drop under us if we don’t give them an hour or two,” he said, quietly.  “They ’re both dead beat.”

Murphy muttered something, incoherent and garnished with oaths, and the moment he succeeded in releasing the buckle, sank down limp at the very feet of his horse, rolling up into a queer ball.  The other stared, and took a step nearer.

“What’s the matter?  Are you sick, Murphy?”

“No—­tired—­don’t want ter see—­thet thing agin.”

“What thing?”

“Thet green, devilish,—­crawlin’ face—­if ye must know!” And he twisted his long, ape-like arms across his eyes, lying curled up as a dog might.

For a moment Hampton stood gazing down upon him, listening to his incoherent mutterings, his own face grave and sympathetic.  Then he moved back and sat down.  Suddenly the full conception of what this meant came to his mind—­the man had gone mad.  The strained cords of that diseased brain had snapped in the presence of imagined terrors, and now all was chaos.  The horror of it overwhelmed Hampton; not only did this unexpected denouement leave him