d have a fine old time getting out if you hadn't brought
that ball of twine!"

"Tell you what we'll do," Sandy said, as the boys turned their faces
down the gangway, "we'll pass around the next shoulder of rock and then
shut off our lights. Perhaps the kids who gave the cry of the pack in
there will then show their light again."

"That's a good idea, too!"

The boys came at length to a brattice, which is a screen, of either wood
or heavy cloth, set up in a passage to divert the current of air to a
bench where workmen are engaged, and dodged down behind it, first
shutting off their lights, of course.

"Now, come on with your old light," whispered Tommy.

As if in answer to the boy's challenge, the light showed again,
apparently but a few yards away from their hiding place.

A moment later the call of the pack, sounding louder than before, rang
through the passage. The boys sprang to their feet and switched on their
lights.

"Why don't you come out and show yourselves?" shouted Tommy.

"I don't believe you're Scouts at all!" declared Sandy.

There was no answer. The boys could hear the drip of water and the
purring of the current as it crept into a lower gangway, but that was
all.

"That settles it for tonight!" exclaimed Tommy. "I'm not going to hang
around here waiting for Boy Scouts who don't respond to signals!"

"That's me!" agreed Sandy. "We'll go to bed and think the matter over.
There may be some way of trapping those fellows."

"Suppose it should be Jimmie Maynard and Dick Thompson?" asked Tommy.

"Then we'd have the case closed up in a jiffy!" was the reply.

Before leaving that particular chamber, Tommy selected a large round
piece of "gob," placed it in the center of the open space, and laid
another small piece of shale on top of it.

"What are you doing that for?" demanded Sandy.

"Don't you know your Indian signs?" demanded the boy. "That means 'This
is the trail.' Now I'll put a stone to the right, and that will tell
these imitation Boy Scouts to turn to the right if they want to get
out."

"I guess they can get out if they want to," suggested Sandy.

Thirty or forty feet further on, where, following the string, the boys
turned again, this time to the left, Tommy laid another signal which
showed the direction to be taken.

"There," he said with a grin, "we've started them on the right path. If
they don't want to follow it, that isn't our fault!"

"We must be getting pretty near the