When, on the night before, the time had come for Ralph's watch to end,
his sister had awakened him, and when the captain, in his turn, was
aroused, he had not known that it was not the boy who had kept watch
during his sleep.

In the course of the morning Mrs. Cliff and Edna, having been filled
with an intense desire to see the wonderful subterranean lake, had been
helped over the rocky barrier, and had stood at the edge of the water,
looking over to where it was lighted by the great chasm in the side of
the rocks, and endeavoring to peer into the solemn, cavernous distance
into which it extended on the right. Edna said nothing, but stood
gazing at the wonderful scene--the dark, mysterious waters before her,
the arched cavern above her, and the picture of the bright sky and the
tops of the distant mountains, framed by the sides of the great opening
which stretched itself upward like a cathedral window on the other side
of the lake.

"It frightens me," said Mrs. Cliff. "To be sure, this water was our
salvation, for we should have been dead by this time, pirates or no
pirates, if we had not found it. But it is terrifying, for all that. We
do not know how far it stretches out into the blackness, and we do not
know how far down it goes. It may be thousands of feet deep, for all we
know. Don't go so near the edge, Ralph. It makes me shudder."

When the little party had returned to the cavern, the captain and the two
ladies had a long talk about the lake. They all agreed that the existence
of this great reservoir of water was sufficient to account for the
greenness and fertility of the little plateau outside. Even if no
considerable amount of water trickled through the cracks in the rocks,
the moisture which arose from the surface of the water found its way out