of an hour watching the light
come and go, but there was the danger of their being inclosed in some
portion of the cavern where the roof was low, and the boat would be made
a prisoner within a prison. So Josh urged the boat forward towards
where Mr Temple had been so busy with his researches, and after a
little examination he bade Will cover the lanthorn with his jacket.

"It's a long time since I were in here," he said; "but I think as the
air-hole ought to be somewhere about here. One moment, Will, lad; hold
the light up and lets see the roof."

The rocky summit was in the highest part, some twelve feet above their
heads, and satisfied as to this, Josh had the light darkened, and then
began to look upward.

"No," he said. "Must be the next. Show the light."

He thrust the boat along once more, grinding and bumping over fragments
of rock, till they had passed under another low part of the roof, when
this rose once more, and the lanthorn being hidden Josh pointed upward
to a narrow crack, through which came a faint light.

"There y'are," he said. "Don't matter how high the water gets, we can
get plenty of fresh air. Tide won't get up there."

The position seemed more hopeful now, for the tide would have to rise
fourteen or fifteen feet to carry them to the roof; and though in
certain places from low water to high water might be perhaps forty feet,
they were now so near the height of the tide that it was not likely to
rise much farther.

"Don't be frightened, Taff, old chap," said Dick in a whisper; "father's
with us, and he'll mind that we don't get hurt."

"I'm not going to be frightened," said Arthur coolly; and then Mr
Temple began to talk cheerily as he stood up in the boat and held the
lanthorn here and there; but first of all Will noticed that he took his
geological hammer and chipped the rock on a level with the water, and
soon after he made a clear bright sparkling chip about a foot higher,
the granite rock glittering in the feeble rays of the lanthorn.

"I should not be a bit surprised if a good lode of metal were discovered
here," said Mr Temple; and he went on chatting lightly about mines and
minerals and Cornwall generally, but somehow he could not draw the
attention of his companions from that bright mark on the rock, towards
which the water was constantly creeping, and then seemed to glide away,
as if exhausted with the effort.

And certainly it was a horrible position to sit there with n