Let that be as it may, here the tunnel extended stretching its snake-like course before me.  Along it I carefully felt a passage, nervously gripping the knife hilt, and vainly seeking to distinguish definite outlines amid the darkness.  My groping feet encountered numerous obstructions along the path—­here a pile of loosened earth over which I plunged headlong, or a flat stone dropped by the rotting away of its supporting prop, or some sharp declivity, as though softer earth had yielded to rude implements; yet it became evident from the start that the tunnel level rapidly descended, boring deeper and deeper into the bosom of the earth.  Finally, my fingers came into contact with small fragments of rock strewing the side walls, and I comprehended I must already be beneath the base of that rounded mound upon the summit of which the house of Naladi stood.  What worried me most was to what end this tunnel was made.  Such vast labor had surely never been performed without adequate purpose.  Besides, completed, the passage was well cared for.  I met frequently in my blind groping with evidences of comparatively recent labor.  Yet for what purpose was it designed?  Where did it lead?  To my bewildered judgment the general trend appeared northward; but that would carry it directly across the broadest portion of the upper basin.  To have an unconcealed entrance in the centre of that unprotected, open plain would be foreign to savage nature; while to imagine that such a tunnel as this, from which a vast amount of earth had been borne upon the backs of workmen, could extend below the full extent of that valley, was beyond conception.  Besides, the air was light and pure, as sweet to inhale as if it blew directly upon me from the open sky; itself proof positive that some opening could not be far distant.

Thus questioning, I groped slowly forward.  To one accustomed to living in the open there is something peculiarly oppressive in being cooped within the confines of such narrow entries, and being compelled to reflect upon the immense mass of rock and earth resting above, and prevented from crushing him down into everlasting silence only by insignificant props of wood, whose melancholy groaning in the darkness bore evidence of the vast weight they upheld.  There was nothing for me but to struggle onward, although I do not claim that it was without quaking heart, or many a start at odd noises echoing and re-echoing along that grim gallery.  It is comparatively easy to be courageous where the peril is of a nature to which we have long accustomed ourselves, but many a trained nerve gives way before little ventures amid the unknown.  I am told that soldiers coming to these colonies—­veterans who had faced unflinchingly the flames of battle—­will tremble and shrink like frightened girls at the slightest sign of a storm at sea; and there was once a famous war-chief of the Shawnees, who had fought fiercely with tomahawk and knife, yet who fell dead at the