don't walk out, and when they do so, we'll hold them up with our guns
until we can build up a barrier which will keep them in."

"One of the boys certainly must understand the code we are so anxious
about," Fenton observed. "That's the kid we want. We've certainly got to
find out what that message contains! If the people in the east are
trying to steal our plans, we certainly ought to know it!"

The boys, however, heard nothing of this talk and passed on down the
north side of the creek. As soon as they came opposite the cavern, in
sight of the light once more, they stopped and began signalling.

As they did so, Cameron and Fenton came nearer and waited anxiously for
the lads to enter the cavern.

"I'd like to know what all that signalling means!" said Cameron.

"Boy Scout signals," replied Fenton.

"You can't read them, can you?" asked the miner.

"Of course not," replied Fenton, "I'm no Boy Scout!"

The boys continued to signal back and forth until the situation was
fairly well understood. Will and Ed knew that Bert had been found and
that all three were barricaded in the cave.

They were disposed to make their way to the rescue of the boys without
further delay, but George advised them to wait until it became darker,
as Cameron might return at almost any moment. The news that Bert had
regained consciousness was very welcome and, confident of their ability
to thwart the plans of the miner, the boys looked forward to quiet hours
in the cabin.

Of course the boys had no suspicion that their enemies were close at
hand watching every movement. Cameron and Fenton became impatient, after
a time, and began advancing slowly toward the boys, who were now not
very far from the mouth of the outer cavern.

Something better than an hour passed, and then George signalled from the
interior of the cavern that it might be well for the boys to come up and
begin the work of removing the rocks which barred their egress.

"Sneak In," George signalled. "Don't show yourself more than you have
to. Cameron may be about! It may be that he has seen our signals
already!"

Sandy replied that he had not discovered any indications of the presence
of the miner, and the two boys advanced to the shelf of rock which faced
the opening. It was nine o'clock then.

"What's that strange noise?" asked Will as they moved along the shelf.

"You've got me!" replied Ed, "The ground's tipping!"

There came a deafening crash and the whole face