sort of communication with him. This, under the circumstances, was
exceedingly difficult, as it was not likely that the Irishman would
suspect that his young friend had succeeded in reaching the outside until
he had received strong proof of it. Very fortunately, however, the couple
possessed a code of signals which were easily understood, if they were
only heard.

"I will try him on our old call," said Fred, as he crept as close to the
edge as he deemed safe, and emitted a whistle that must have extended far
within the cave.

"If he hears that, he will understand it," he added, turning his ear, so
that he could catch any response; but the dim, soothing murmur of the
cascade was the only sound that came up from the cavernous depths.

"He must be there--he must be there, and he will come back, so he will
catch the signal sooner or later."

There was one aspect of the business which had not yet occurred to Fred,
and which was likely to inure to the benefit of Mickey O'Rooney, the
gentleman who just then stood in need of everything that came along in
that line. The Apaches were skillful and wise enough to learn from the
trail which had first told them the story, that a boy and man had been
caught in the cavern, and it was very evident that they all believed that
there was no other avenue of escape except that by which they had entered.
At the same time, their knowledge of the peculiarities of their own
country must have convinced them that it was possible that other openings,
of which they knew nothing, might exist, and might become known to the
prisoners.