and then--why, it will go down again--that's all."

"But suppose it fills this cave?"

"Nonsense! It can't. I'm not going to suppose anything of the sort.
Now come on. Let's see if we can move this rock."

Together they pressed on the stone with all their strength. They might
as well have tried to budge the side of a mountain. The rock was
firmly wedged in place.

"It's no use," spoke Andy, in a dull, hopeless tone.

"Oh, don't give up so easily," urged his brother. "If we can't do it
one way, we may another. See, it has slid down in a sort of groove.
Only a little ridge of rock on either side holds it in place. Now if
we can break away those upright ridges, which are like the pieces on a
window sash up and down which the window slides, we may be able to push
the rock out. Let's try. Use your knife and take a rock for a hammer."

Frank placed his torch on a ledge of rock, tying the spring down by a
piece of cord so that the light would focus on the big bowlder. Then,
with their pocket-knives as chisels, and stones as mallets, they began
their futile attempts to cut away the holding ridges of rock.

That it was a futile attempt was soon made evident, for their knives
slipped off the flint-like stone, and several times when the blades
unexpectedly shut, the lads received severe cuts on their hands.

Suddenly Andy uttered an exclamation:

"The water! It's getting deeper!" he cried

It was up to their knees now.

"Of course it getting deeper," said Frank, with a cheerfulness that he
was far from feeling. "The tide isn't half in yet."

Andy shuddered.

"What will we do when it's high water?" he asked.

Frank did not answer, but kept on chipping away at the rock. He
managed to break off several pieces, but it was easy to see that it
would take much more work to loosen the retaining ridges so that the
bowlder that imprisoned them would fall outward.

"There it goes!" suddenly exclaimed the older brother in despair.
"I've broken my knife blade! You'll have to do all the work, Andy."

"Oh, what's the use?" sighed the younger lad. "The water is coming in
faster. See, it's up to our waists now, and the tide is nowhere at
full! We're doomed, Frank!"

"Not a bit of it. See that ledge of rock up there? We'll climb up on
it and wait until the water goes down. Then maybe someone will come
for us, or we can get out. Climb up, Andy. We won't try to break off
any more rock."

Frank helped his b