g," said Vince, as he rose up, finding that
his head nearly touched the shell-encrusted roof.

"Yes; to force our way out," said Mike excitedly. "We must before it's
too late."

"It is too late, as I told you before," said Vince sharply. "Look for
yourself. Can't you see that the arch is too small for the sides of the
boat to get through? and at any moment another of those waves may come
in. It's all right, Ladle, if you'll only be firm."

"I'll be as firm as you are," said the boy angrily.

"Then help me push her along."

Mike pressed his hands against the roof, Vince did the same; and they
both thrust hard, but in spite of all the boat did not stir.

"Why, you're pushing to send it in," said Mike.

"And you to drive it out! What nonsense! This place is sure to get
bigger inside, where the water has washed it out. We must get right in,
beyond where the water rises."

Mike shuddered; for the silence and darkness of the place would, he
felt, be horrible, and all the time he knew that the water would be
gradually chasing them, like some terribly fierce creature, bent on
suffocating them in its awful embrace.

Vince's was the stronger will; and his companion yielded, changing his
tactics, and forcing the boat along for some distance before there was
any change in the roof, which crushed down upon them as low as ever, and
Mike began once more to protest.

"It's of no use," he said: "we may as well be smothered where we can see
as here, where it is so dark. Let's go back as far as we can."

"No; I'm sure this place will open out more if we go farther in."

At that moment there was a loud, plashing noise far inward, and this
raised such loud reverberations that Mike was fain to confess that the
roof must be far higher.

Vince took advantage of this to urge his companion on; and a minute
later they could not touch the rock above them with their hands, while a
little farther on it could not be reached with an oar.

"Yes, it's bigger," granted Mike; "but we shall be suffocated all the
same. There can't be enough air to last us till the tide goes down."

"We shall see," said Vince; and then, quite cheerily: "I say, this is
better than wading, the same as we did in the seal hole."

"Yes, but there are seals here. I heard them."

"Yes, so did I, but what of that? We mustn't interfere with them, and
they won't with us. Besides, we're in a boat now, recollect."

Mike recollected it well enough, but it