nothing more.

Then we crept back up the wet ledge, and once more stood on dry ground.

The surface was perfectly level, and we set off at a brisk pace, hand
in hand, directly away from the lake. But when, about a hundred yards
off, we suddenly bumped our heads against a solid wall of rock, we
decided to proceed with more caution.

The darkness was intensified, if anything. We turned to the right and
groped along the wall, which was smooth as glass and higher than my
best reach. It seemed to the touch to be slightly convex, but that may
have been delusion.

We had proceeded in this manner some hundred yards or more, advancing
cautiously, when we came to a break in the wall. A few feet farther
the wall began again.

"It's a tunnel," said Harry.

I nodded, forgetting he could not see me. "Shall we take it?"

"Anything on a chance," he answered, and we entered the passage.

It was quite narrow--so narrow that we were forced to advance very
slowly, feeling our way to avoid colliding with the walls. The ground
was strewn with fragments of rock, and a hasty step meant an almost
certain fall and a bruised shin. It was tedious work and incredibly
fatiguing.

We had not rested a sufficient length of time to allow our bodies to
recuperate from the struggle with the torrent; also, we began to feel
the want of food. Harry was the first to falter, but I spurred him on.
Then he stumbled and fell and lay still.

"Are you hurt?" I asked anxiously, bending over him.

"No," was the answer. "But I'm tired--tired to death--and I want to
sleep."

I was tempted myself, but I brought him to his feet, from some impulse
I know not what. For what was the use? One spot was as good as
another. However, we struggled on.

Another hour and the passage broadened into a clearing. At least so it
seemed; the walls abruptly parted to the right and left. And still the
impenetrable, maddening darkness and awful silence!

We gave it up; we could go no farther. A few useless minutes we
wasted, searching for a soft spot to lie on--moss, reeds, anything. We
found none, of course; but even the hard, unyielding rock was grateful
to our exhausted bodies. We lay side by side, using our ponchos for
pillows; our clothing at least was dry.

I do not know how long I slept, but it seemed to me that I had barely
dozed off when I was awakened by something--what?

There was no sound to my strained ears. I sat up, gazing intently into