ahead to where he saw a more narrow place that
would enable him to leap across from the right to the left side of the
channel.

And then, while the others hung back for a moment, and Nort thus dashed
ahead alone, his companions saw him quickly disappear. The wall of
water suddenly rushed forward, but it never came quite to the place
where the party of five now stood in nameless terror--five, for Nort
had disappeared into the depths of the stream that had so mysteriously
appeared again out of the blackness.

From whence it came, and whither it was rushing, not to foam entirely
over that startled group, none in it could say. But it had engulfed
Nort--that they had seen.

CHAPTER XXI

THE FIGURE ON THE ROCK

Horror and surprise held the five speechless for a moment. Then, as
they heard the noise of the rushing water, and saw, by the light of
their lanterns, that it came almost to them, but suddenly turned to the
right, they came to their senses.

"Nort! Nort!" yelled Dick, his voice being flung back at him in echoes
from the rocky, vaulted roof of the tunnel.

"What in th' world happened?" asked Old Billee in trembling accents.

"Nort fell into the stream, and was carried away," answered Bud, his
voice choking.

"But why doesn't the water reach us?" asked Snake.

"That's what we'll have to find out," asserted Bud, bravely. "Come on!"

"But be careful," cautioned Billee. "Something may happen t' us, an'
then we can't help Nort! Go easy!"

He spoke only in time, for the next moment, with an exclamation of
horror, Bud and Dick, who had forged ahead, recoiled back.

"Look out!" shouted Bud, and he made such a lurch backward to recover
his balance that the lantern was flung from his hand. It dropped, as
they all could see, into the midst of black, swirling waters, white
foam-capped on top.

And it was into this stream that Nort had fallen and been carried away,
and into this stream that Bud and Dick had been nearly precipitated as
they dashed forward.

Bud's lantern was extinguished with a hiss as the waters penetrated it
and covered the wick. It sank from sight, but not before it had, in a
flash, illuminated the surface of the water.

"It's a good thing we took the right-hand side," said Billee, as he and
the others saw what it was that had caused the water to rush almost to
their feet and then branch off. "I mean it's a good thing, for it may
help us to solve the mystery. But as for poor