on of considerable size.

"Nothing doing here!" Will exclaimed as he flashed his searchlight
around the place. "This chamber looks as if there hadn't been an ounce
of coal mined here for a hundred years."

"Then let's get out," George proposed, "and make our way back to the
shaft if possible. If we can't, we'll make noise enough to attract
Canfield's attention and let him come and lead us out."

"Here we go, then," cried Will, giving the boat a great push toward the
dip. "We can't get out any too fast."

The boat came up against a solid projection of rock!

"I don't seem to see any way out!" George exclaimed.

"Well, it's there somewhere!" declared Will.

"I see it now!" cried George. "It's under water!"

"Under water?" repeated Will.

"Yes, under water!" answered George. "If we don't get out of this hole
before the pumps get to working we'll have to swim!"

Will turned his searchlight on the dip and saw that it was now full
clear to the down dropping roof.

"I guess we'll have to swim," he agreed.

"That black water doesn't look good to me," George exclaimed with a
little shudder. "It seems to me that I can see snakes and alligators
wiggling in it from here. Looks worse to me than the swamps of the
Everglades! And there was a quart of snakes to every pint of water down
there!"

"But we got to swim just the same!" urged Will. "In half an hour from
now the air in this chamber will be unbreathable. There is no vent at
all, now that the water fills the dip, and the coal gas is naturally
seeping in all the time."

"That's all right, too!" admitted George. "But I'm not going to jump
into that black water until I have to. If a rope or something should
twine around my legs while I was in there, I'd drop dead with fright!
Besides," he went on, "the chances are that Canfield will get the pumps
going before long now."

The boys waited for a long half hour, during which time the water rose
steadily. It seemed certain that the mine was about to be flooded
throughout all the lower levels.

"Tommy and Sandy may have bumped into just such a situation as this,"
Will said, as he pushed the boat from side to side in the hope of coming
upon some exit from the place.

"Serves 'em good and right!" exclaimed George.

Will chuckled to himself and held a wet hand high up toward the roof of
the chamber or passage.

"There's a current of air here!" he said.

"Then we won't smother to death!" George grunted.

"And, loo