we were brought to a halt. A sheer wall of rock had
appeared before us, with no chink through which a mouse could have
slipped. There was no escape for us there.

We stood with bitter hearts staring at this unexpected obstacle. It
was not the result of any convulsion, as in the case of the ascending
tunnel. The end wall was exactly like the side ones. It was, and had
always been, a cul-de-sac.

"Never mind, my friends," said the indomitable Challenger. "You have
still my firm promise of a balloon."

Summerlee groaned.

"Can we be in the wrong cave?" I suggested.

"No use, young fellah," said Lord John, with his finger on the chart.
"Seventeen from the right and second from the left. This is the cave
sure enough."

I looked at the mark to which his finger pointed, and I gave a sudden
cry of joy.

"I believe I have it! Follow me! Follow me!"

I hurried back along the way we had come, my torch in my hand. "Here,"
said I, pointing to some matches upon the ground, "is where we lit up."

"Exactly."

"Well, it is marked as a forked cave, and in the darkness we passed the
fork before the torches were lit. On the right side as we go out we
should find the longer arm."

It was as I had said. We had not gone thirty yards before a great
black opening loomed in the wall. We turned into it to find that we
were in a much larger passage than before. Along it we hurried in
breathless impatience for many hundreds of yards. Then, suddenly, in
the black darkness of the arch in front of us we saw a gleam of dark
red light. We stared in amazement. A sheet of steady flame seemed to
cross the passage and to bar our way. We hastened towards it. No
sound, no heat, no movement came from it, but still the great luminous
curtain glowed before us, silvering all the cave and turning the sand
to powdered jewels, until as we drew closer it discovered a circular
edge.

"The moon, by George!" cried Lord John. "We are through, boys! We are
through!"

It was indeed the full moon which shone straight down the aperture
which opened upon the cliffs. It was a small rift, not larger than a
window, but it was enough for all our purposes. As we craned our necks
through it we could see that the descent was not a very difficult one,
and that the level ground was no very great way below us. It was no
wonder that from below we had not observed the place, as the cliffs
curved overhead and an ascent at the spot would have seem