here," she continued.
"It's all a guess as to how thick that wall of earth and rock is, and
we may be using on it the strength that we need for other things. If
you had an implement of some kind it would be different. But with your
bare hands together with what little help I can give you it may be
impossible."

"Yes," he was forced to concede, "I can't go on forever. Sooner or
later my strength will give out. But what can we do but keep on
trying? I'd go raving mad if I didn't keep on taking the one little
chance we have."

"But is it the only chance we have?" she argued. "Did you bring your
revolver with you?"

For answer he took it out of his belt and put it in her hand.

"Have you any extra cartridges?" she asked.

"Not a single one, but the revolver itself is fully loaded. That's
just six we have to count on."

She was silent for a moment.

"There isn't any likelihood we'll have to use these for defending
ourselves," she said at length. "There doesn't seem to be any living
thing in this cave of which we need to be afraid. But, nevertheless,
suppose we keep two for emergencies. That would give us four to
experiment with, wouldn't it?"

"Experiment? How?" he inquired.

"I was thinking that perhaps father"--here her voice faltered a
little--"and Tyke might be somewhere in the neighborhood hunting for
us. If we should discharge the revolver they might possibly hear one
or more of the shots and get some idea of where we were. I know it's
only a forlorn hope, but we've got to try everything just now."

"It's a good idea!" exclaimed Drew, though he knew in his heart how
slender a chance it offered. "And in the meantime, I'll keep on
digging, so that if the shots aren't heard we won't be any worse off
anyway. You fire the four shots at intervals of a minute or two and
we'll see what happens."

He went savagely to work again and Ruth at short intervals discharged
the revolver. The noise and the echoes in that compressed space were
deafening and it certainly seemed as though the sound ought to
penetrate to the world outside.

But though they fairly held their breath as they listened for a
response, no answering sound penetrated from the outside into the
cavern, and their hearts sank as they realized that one more of their
few hopes had failed them.

"It's of no use," observed Ruth sadly, as she handed the weapon back to
Allen. "Either they didn't hear the shots, or, if they did, they
though