his search, his firebrand held over
his head.

It was a discouraging journey when the end was reached. Before him arose
a solid wall not less than twenty feet in height, at which elevation the
cavern appeared to continue. Allen gazed up at the wall with a hopeless
look on his face.

"Humph! How in the name of creation am I to climb up there?" he
muttered. "It's as steep as the side of a house and twice as slippery.
If I can't find some sort of stepping places I reckon I'm beaten and
booked to go back to where I started from."

Waving the firebrand to make it burn the brighter, Allen began to
scrutinize the face of the wall before him. He started at one end,
resolved that not a foot of the surface should escape him.

He had traveled along some fifteen feet when he came to something that
made him start back in astonishment.

"Great Caesar!"

Before him were a number of letters, cut in smooth rock, which was
apparently quite soft. The letters read:

BARNABY WINTHROP'S MINE.

Allen stared at the letters on the rock as if he had not spelled out the
words aright. But there was no mistake. They really read "Barnaby
Winthrop's Mine."

"Well, if this isn't the most wonderful discovery ever made!" ejaculated
the young man, finally. "So this is the place that Uncle Barnaby talked
of as being the richest claim in Idaho. I wonder how he ever found it?"

While Allen stood close to the rocky wall he reached the conclusion that
his uncle must have come there by the river, but whether a voluntary or
involuntary passenger he could not decide. He knew Uncle Barnaby was
exceedingly fearless, but was there any human being who would take the
awful risk of a journey on that underground river, not knowing to where
it led?

"He must have been caught, just as I was," said Allen to himself, at
last. "And that being so, the question is, how did he manage, after he
was once here, to get _out_?"

While Allen was debating this question he cast his eyes about for some
means of scaling the wall. He walked along its face until the very end
was reached, and there, to his joy, discovered a dozen rudely cut
niches, some of them were close together and others nearly a yard apart,
but, with the end of the firebrand between his teeth, he had no great
difficulty in pulling himself up to the level of the flooring of the
cavern above.

Allen now found himself in an opening not over fifty yards square. The
roofing was hardly out of reach, and th