b the walls, Bob."

"Whew! then perhaps I'd better be keeping an eye out as we go along,
and see how the land lies?" suggested the boy from Kentucky.

"A good idea, Bob. Just notice where the chances look half-way decent
for a climb. And remember, at the same time, that the wave may be all
of thirty feet deep when it sweeps through here."

"You don't say? That would mean some hustling then to get up out of
reach, Frank."

"I reckon it would. Look out for that nasty rock; it nearly tripped
me, Bob."

"What was that flash, Frank? Don't tell me it was lightning, real
lightning, and that the long delayed storm is going to break right now,
when it's got us cooped up in this hole?"

"It was lightning, all right. There, that proves it!"

Frank's words were drowned in a crash of genuine thunder that made the
foundations of the mountain shake just as much as the mad efforts of
the imprisoned geyser had ever done.

"No mistake about that sort of thing," cried Bob, as he stumbled along
after his chum. "There it comes again, Frank. I guess I'd better be
picking out a good way up the wall somewhere, for it looks like we'd
have to climb!"

Frank was doubtless sizing up the situation in his mind. He was also
listening for some sound which he expected to hear, but which was going
to prove a very unwelcome one.

"No use going any further, Bob, if so be you've seen anything that
looks promising here," he declared, when the reverberations of the
thunder had ceased to echo through the canyon.

"Then you think we're going to get caught here, Frank?" questioned the
other.

"I'm afraid to take the chances of keeping on any further. It may be a
long run to the next broken wall, that offers us a chance to climb.
Some places the sides go up as smooth as glass. Have you see an
opening here, Bob?"

"Yes, yes, right on the left, Frank!" exclaimed Bob, eagerly. "I
couldn't see so very far up, but it looks good to me."

Frank turned his gaze up to where his comrade pointed.

"I think it's rough as far as that ledge," he said; "and let us hope
that will be out of the reach of the water. Come on, Bob; let's see
how you can climb; but be careful, boy, be mighty careful!"

"Frank, that roaring sound didn't seem like the others we've been
hearing; d'ye think it means anything has happened?" Bob called, as he
started to clamber up the rough face of the wall, taking advantage of
every jutting rock, and showing a nimbleness