Frank, "and now having solved the great mystery--let's get back to
work."

The three adventurers went at the job with a will. The line was
about a hundred feet long and the method of procedure was this:
Frank tested the straightness of the line, as accurately as possible
with his eye, while Ben and Harry carried it stretched between them.
The end of each hundred feet was signalized by a stone, and Harry,
who was at the end of the line, carried his end to this mark before
they laid out a fresh hundred feet. In this way they must have
measured off very nearly half-a-mile of the mountain-side when Frank
gave a sudden sharp cry and pointed to a depression in the dark
range immediately below them. As the others looked they echoed his
cry and gave a dash forward.

Directly beneath them, about in the center of the little dip, was a
cairn of rough stones perhaps four feet in height. In a few bounds
they had reached the pile, which they knew meant the discovery of
the ivory cache and the end of the most difficult part of their
expedition. Little did they imagine the amazing things that were
yet to happen to them and of which they were but on the threshold.

"Good Lord, look at that, boys!" exclaimed Frank, as they stood at
the foot of the cairn.

There was a good reason for the boy's exclamation.

Distributed around the base of the pile were a dozen or, more human
skulls.