ad slept, but they were awakened by the
ringing of a bell and felt the vessel was coming to a stop. They were
still far beneath the surface; indeed, the boat was resting on the
bottom, for in the light of two or three powerful search-lights they saw
a wide succession of submerged hills, vales, and rugged cliffs. Before
them was a great mountain-side and in it they saw the mouth of a dark
tunnel. They had scarcely noticed it before the vessel rose a little and
glided toward the tunnel and entered it. Through the glass walls they
could see that it was narrow, and that the ragged sides and roof were
barely far enough apart to admit them.

Suddenly one of the men came in and drew a curtain down behind them,
and, with a vexed look on his face retired.

When he was gone Johnston put his lips close to Thorndyke's ear and
whispered:

"Did you see that?"

"See what?"

"Just as he drew the curtain down I saw what looked to me like a cliff
of solid gold. It had been dug out into a cavern in which I saw a vessel
like this, and men in diving suits digging and loading it."

This took the Englishman's breath away for a moment, then he remarked:
"That accounts for the heel-tap we found; who knows, these people may be
possessors of the richest gold and silver mines on earth."

The bell rang again. "We are rising," said Johnston. "If this is the
only way of reaching the king's domain, we could never get back
to civilization unless they release us of their own accord, that's
certain!"

"Heavens, isn't it still!" exclaimed the Englishman. "The machinery
of this thing moves as noiselessly as the backbone of an eel. I wish I
could understand its works."

"I am more concerned about where we are going. I tell you we are being
taken to some wonderful place. People who can construct such marvels of
mechanical skill as this boat will not be behind in other things; then
look at the physiques of those giants."

Just then the man who had drawn down the shade came in and raised it.
Both the captives pretended to be uninterested in his movements, but
when he had withdrawn they looked through the glass eagerly.

"See," whispered Thorndyke, in the ear of his companion, "the walls are
close to us, and are as perpendicular as those of the lake in which they
found us."

Johnston said nothing. His attention was riveted to the walls of rock;
the vessel was rising rapidly. An hour passed. The soft music had
ceased, and the air seemed less dens