Bob.

"That's so," returned his chum; "just as Nick said; we're here, and
we've just got to stick it out, no matter what comes."

"But do you take any stock in what Peg said about an avalanche?" asked
Bob.

"Mighty little," Frank replied. "This mountain is made up mostly of
solid rock. That's what makes lots of people believe in the volcano
idea. A slide would be hard to start here, and it just couldn't carry
much along with It. Where mountains have sides made up of earth and
loose rocks, that happens sometimes."

"I'm glad to hear that," remarked the other. "But there comes another
shake. Whew! feel how she trembles, Frank! Whatever sort of power can
it be that makes this noise and shivering sensation?"

Frank waited until the convulsion had passed before replying.

"I've got a strong suspicion, Bob," He said, finally; "and it's
something that came into my mind since _feeling_ the sound, for that's
the only way I can express it. Now, what does it make you think of,
most of all?"

"I did think it was thunder," declared Bob; "but now it seems to me the
only thing I can compare it to is the beating of the terrible billows
against the coast away up in Maine, when a fierce northeast storm is
blowing. They seemed to make the rocks quiver just as this does now."

If Frank had intended to reply to this remark he was prevented by
something unexpected that happened just then. This time it was not the
furious roar of the unknown force within the mountain that disturbed
him; but a cry that rang out shrilly.

"Help! Help!"

Bob clutched his companion's arm.

"Something has happened to Peg!" he exclaimed. "Perhaps the guide has
thrown him over, and he's lost, and scared nearly to death!"

But Frank was more accustomed to reading voices in the open than was
his chum.

"No, you're wrong there!" he cried, "that's Spanish Joe yelping; and he
must be in a bad hole to call for his companions. Come on, Bob, we've
just got to see what we can do to help him. Rascal that he is, he's
human. Follow me!"

CHAPTER XV

SPANISH JOE DROPS A CLUE

"Where can he be, Frank?" cried Bob, after they had been climbing for
several minutes up the side of the rough mountain, almost groping their
way, such was the darkness around them.

"Listen!"

"Help! Nick, this way, quick, or I'll go under!" came a shrill shout,
only a little way above them.

They started for the spot; but before they had taken half a dozen s