tter grip, and this was a wise provision, for it was desperate
holding at best.

Frank followed his brother, and then, at the last stand, they clung
there together, listening to the lapping of the water that, raised up
as they were, even now wet their legs.

How long they clung thus they did not know. It seemed a long time, but
it could not have been more than fifteen minutes they agreed afterward,
for the water did not gain much. But suddenly the silence of the night
outside was broken by a loud report.

"Signal guns!" exclaimed Andy. "Some vessel is in distress."

"No, that's thunder!" said Frank. "There's a storm coming up. But we
won't know it--in here."

"I hope our boat is safe, and that the _Gull_ is well anchored," went
on the younger lad anxiously.

"As if that mattered," thought Frank, but he did not say so. He began
to think they would never have any further use for their craft. He
choked back the dreadful fear that seemed to take possession of him.

Once more came a terrific clap of thunder, and it seemed to shake the
very island to its center.

"It's a fierce one," murmured Andy.

In quick succession came a number of awful reports. The earthy wall to
which they were clinging seemed to tremble. The water gurgled below
them, rising higher and higher.

"I wonder--" began Andy, after a terrific clap, but his words were
silenced in the thunderous vibration that followed. It was the hardest
clap yet, and the boys felt a tingling, numbing sensation in their
fingers.

"That struck near here!" yelled Frank.

His face was turned upward toward the roof of the cavern. He felt
something falling on his cheeks. It seemed to be particles of dirt.
Then he felt a dampness that was not from the waters below him. More
particles fell.

"What's the matter?" cried Andy. "Something is happening. What is it?"

Before Frank could answer, had he known what was taking place, there
came a loud splash in the water at Andy's left.

"Is that you Frank? Have you fallen?" he called desperately.

"No, I'm here," replied his brother. "That must have been part of the
side or roof of the cave jarred off by the thunder. Hold fast, Andy."

There came a second splashing sound in the water, followed by another.
The drops of dampness and particles of earth continued to rain into the
faces of the lads.

"The cave's crumbling in!" cried Andy. "The roof is falling."

"Hold--" began Frank.

A roar interrupted