rs coming from the dark reaches of the cavern,
but they were not quite certain.

"There may be real Beavers in here for all we know!" suggested Will.

"That's all you know about it!" chuckled George. "Beavers only operate
in running water."

"Well, isn't that water out there running?" asked Will.

"No jokes now!" replied George. "I've got all I can endure now without
standing for any of your alleged witticisms!"

While the boys sat in the boat, occasionally moving it from side to
side, a shaft of light appeared directly above the point where the shale
had been heaped up. It moved swiftly about for an instant and then
dropped out of view. It was a moment before either boy spoke.

"That's some of Tommy's foolishness!" Will declared.

George repeated the Beaver call several times, but no answer came.

"That's a searchlight, anyway!" insisted Will. "And I don't believe
these ginks in the mines have electric searchlights to lug around with
them!"

Will unshipped an oar and struck the water with the flat of the blade
several times, exerting his whole strength.

"Keep it up!" advised George. "That sounds exactly like a beaver's tail
connecting with the surface of a stream!"

"Yes, keep it up!" cried a voice out of the darkness. "Keep it up, and
perhaps some beaver'll come along and build a dam to get you out of that
mess you're in! You're always getting into trouble, you two!"

"You've got your nerve with you!" exclaimed Will, half-angrily. "Here
you go out in the night and get lost, and we come out after you, and the
mine gets flooded, and we get tied up between the solid wall and a
bend in the passage, and then you blame us for getting into trouble!"

"Can you climb?" chuckled Tommy, throwing the rays of his searchlight on
the boat. "If you can, just mount up on that pile of shale and work your
way through the opening between the two levels. This might have been
used as a sort of an air hole a few hundred years ago," he went on, "but
I'll bet that not one out of a hundred of the miners of today know that
there is an opening here!"

Leaving the boat, the boys mounted the pile of shale and were soon
making their way up the rugged face of the shaft in the direction of the
level, which ran along above the one now being flooded.

"Can you find your way out of this dump, now?" asked Will as the boys
stood with their chums at the end of a long passage.

CHAPTER VII

A TREACHEROUS FOE

"There seems to b