ize as to width, resembling more a rugged passage or
subterranean canal made by nature, regardless of direction or size, than
a cavern; but to the boys it was a weird, strange place, full of awe and
mystery. Every time oar or boat-hook touched the rocky side, there was
a strange, echoing noise. Now and then the keel of the boat grated on
some unseen rock, or was lifted by the water and dropped softly, as it
were, upon some portion of the stony bottom as the water rose and fell.

The opening was left behind, and it seemed horrible to Arthur that calm
coolness with which his father sat still and allowed Josh to thrust the
boat along farther and farther till it became too dark for them to see,
and Josh laid his boat-hook down. As he did so there was a silence for
a few moments, in the midst of which, heard beneath the dripping musical
tones of the falling water, came a curious hissing, whispering sound
from beyond them farther in the cave.

"What's that?" said Arthur in a low voice as he spasmodically caught at
his brother's arm.

Truth to tell, the mystery of the place had impressed Dick, who suffered
from a half self-confessed desire to get out into the daylight once
more; but now came this evident display of dread on his brother's part,
and its effect was to string him up at once.

Laughing at Arthur meant laughing at himself, and he snatched at the
opportunity as Arthur whispered once more, "Dick--Dick--what's that?"

"That?" said Dick in the same low tone. "That's the bogle-booby
breathing. He's asleep now, but when he wakes he'll roll about so that
he'll fill the place with foam."

"Don't you take any notice of him, Master Arthur," said Will gently.
"He's making fun of you. That whispering noise is made by the water as
it runs gurgling up the cracks of the rock and comes back again."

"Cr-r-r-ack!"

Arthur uttered a shrill cry, and Dick burst out laughing.

"Why, it was only a noisy match, Taff," he exclaimed, as, after a loud
cracking scratch, there was a flash of light, and then a clear glow was
shed around by the lantern, whose lamp Josh had just lit, its rays
showing dimly the rugged walls of granite, all wet with trickling water,
while the shadows of the boat and its occupants were cast here and
there.

"Now, Master Dick, if you'll take the lantern and hold it up I'll send
the boat farther in, so as if there be any seals you'll have a chance of
seeing 'em."

"You think there are some then?" sa