of rock."

"That's so, Frank. Wow! but it makes me shiver to even think of it.
Talk about Joe's narrow squeak, it wasn't any worse than mine," and Bob
started to crawl after his better-trained chum.

Two more evidences came to them of the violence of the unseen force
that was making Thunder Mountain shake, before Frank stopped to let his
chum reach his side, so that he might exchange a few sentences.

"Looks like that might be the hole ahead," he ventured.

"I can see something that seems blacker than the night itself; is that
what you mean, Frank?" asked Bob.

"Yes," his chum continued. "When Joe pointed up this way I took note
of just the line, and followed it closely. That was why we came so
near the precipice. And if that is the opening to the cave, we want to
lie here and listen."

"Why, do you really believe the racket comes out of that hole?"
demanded Bob, astonished at the very idea of such a thing.

"Wait and see," replied the other, confidently. "In the meantime,
here's our opportunity to pick up a few candles that will come in
handy."

They had come to a halt directly under a tree; and Bob had already
discovered that the ground was thickly strewn with broken branches.
Some of these were apt to be fat with the inflammable gum that exudes
from certain species of cedar, and would, as Frank said, make splendid
torches.

Frank was already on his hands and knees searching for suitable ones;
and as Bob grasped the idea he, too, set to work.

"I have four already; how do you stand?" asked Frank, presently.

"Just as many--no, here's the fifth one, and the best of the lot," came
the reply from the Kentucky lad, who went into everything with ardor
and enthusiasm.

"That ought to do for us," Frank went on. "And now, listen for all
you're worth, because the war is on again!"

Lying there, Bob heard what seemed to be the first signal. It was as
though some giant hand had tapped the solid rock with his club. Then
faster came the blows, and more and more did the din increase, until it
was fairly deafening. Only for his intense eagerness to hear every
sound Bob might have been tempted to thrust his fingers into his ears
in order to shut out the awful clamor.

To him it seemed as though a thousand anvils were being beaten in
chorus, with a few other minor chords thrown in for good measure.

And what interested Bob most of all, as he crouched there listening,
was the fact that all this dreadful nois