said Gwyn; "but, somehow,
being down here as we were, I seemed to be stunned, and it has always
been hard work to recollect all we went through. I'd forgotten lots of
these galleries and pools and roofs, just as one forgets a dream, while,
going through them again, they all seem to come back fresh and I know
them as well as can be. But what makes this faint rumbling, Sam? Is it
one of the little trucks rumbling along in the distance?"

"No, sir," said Hardock, with a chuckle. "What do you say it is, Master
Joe?"

The lad listened in silence for a few moments, and then said slowly,--

"Well, if I didn't know that it was impossible, I should say that we
were listening to the waves breaking on the shore."

"It aren't impossible, sir, and that's what you're doing," said Hardock;
and the boys started as if to make for the foot of the shaft.

"What's the matter," said Hardock, chuckling. "'Fraid of its bursting
through?"

"I don't know--yes," said Gwyn. "What's to prevent it?"

"Solid rock overhead, sir. It's lasted long enough, so I don't see much
to fear."

"But it sounds so horrible," cried Joe, who suddenly found that the
gallery in which they were standing felt suffocatingly hot.

"Oh, it's nothing when you're used to it. There's other mines bein'
worked right under the sea. There's no danger so long as we don't cut a
hole through to let the water in; and we sha'n't do that."

"But how thick is the rock over our heads?"

"Can't say, sir, but thick enough."

"But is it just over our heads here?"

"Well, I should say it warn't, sir; but I can't quite tell, because it's
so deceiving. I've tried over and over to make it out, but one time it
sounds loudest along there, another time in one of the other galleries.
It's just as it happens. Sound's a very curious thing, as I've often
noticed down a mine, for I've listened to the men driving holes in the
rock to load for a blast, and it's quite wonderful how you hear it
sometimes in a gallery ever so far off, and how little when you're close
to. Come along. No fear of the water coming in, or I'd soon say let's
get to grass."

The boys did not feel much relieved, but they would not show their
anxiety, and followed the mining captain with the pulsation of their
hearts feeling a good deal heavier; and they went on for nearly an hour
before they reached the spot familiar to them, one which recalled the
difficulty they had had with Grip when he ran up the