swim
across to Harry, counting on his voice as a guide; but the conflicting
echoes produced by the slightest sound rendered such an attempt
dangerous.

I crept along that wet, slimy, treacherous surface, it seemed, for
hours. I could see nothing--absolutely nothing; everything was black
void; it was hard to appreciate reality in such a nightmare. On the
one side, nameless dangers; on the other, the unseen, bottomless lake;
enough, surely, to take a man's nerve. My fear for Harry killed
anxiety on my own account. We kept continually calling:

"Harry!"

"Yes."

"Steady."

"Yes. I'm coming along. I say, we're closer, Paul."

I hesitated to agree with him, but finally there was no longer any
doubt of it. His voice began to reach me almost in natural tones,
which meant that we were near enough for the vibrations to carry
without interference from the walls.

Nearer still it came; it was now only a matter of a few feet; Harry
gave a cry of joy, and immediately afterward I heard his low gasp of
terror and the sound of his wild scrambling to regain a foothold. In
his excitement he had forgotten caution and had slipped to the edge of
the water.

I dared not try to go to his assistance; so I crouched perfectly still
and called to him to throw himself flat on his face. How my eyes
strained despairingly as I cursed the pitiless darkness! Then the
scrambling ceased and the boy's voice sounded:

"All right, Paul! All right! Gad, I nearly went!"

A minute later I held his hand in mine. At that point the incline was
at a sharp angle, and we lay flat on our backs. For many minutes we
lay silently gripping hands; Harry was trembling violently from nervous
fatigue, and I myself was unable to speak.

What strength is there in companionship! Alone, either of us would
probably have long before succumbed to the strain of our horrible
situation; but we both took hope and courage from that hand-clasp.

Finally he spoke:

"In Heaven's name, where are we, Paul?"

"You know as much as I do, Harry. This cursed darkness makes it
impossible even to guess at anything. According to Felipe, we are
being entertained by the devil."

"But where are we? What happened? My head is dizzy--I don't know--"

I gripped his hand.

"And no wonder. 'Tis hardly an every-day occurrence to ride an
underground river several miles under the Andes. Above us a mountain
four miles high, beneath us a bottomless lake, round us darkn