like the other cave, has also a cross-shaped formation, and
the treasure should be at the south branch."

"Here it is," whispered George.

"What, the treasure?" was Harry's eager question.

"No; the south branch."

"You are undoubtedly right. There is no other opening."

This branch was followed less than a hundred feet, when a solid white
wall appeared in front, and it was readily seen that the channel
terminated in the chamber.

The floor of this chamber was one mass of uneven projections, entirely
unlike the other parts of the cave, and what was more singular still, it
was fully six feet higher than the floors of the other portions, but it
was absolutely devoid of any treasure, or anything which could contain
such a hoard as the chart seemed to indicate.

"It is just as well," said John, resignedly. "I suppose we have enough
for our purposes."

While crawling down the rough portion which formed the elevated floor of
the chamber Harry slipped, and broke off a portion of the stalagmite
overlaying the side. It was dark beneath.

[Illustration: _Fig. 21. Diagram of the Cross-Shaped Cave._]

"This is not calcareous matter," exclaimed John.

"What is it?" asked both in a breath.

The lights were concentrated on a sample, and as John raised his head he
looked at the boys, and slowly uttered one word:

"Copper!"

The boys did not at first grasp the true significance of the word. It
was marvelous to them that copper should be found there, but John
thought of something else. It offered a possible explanation to the
origin of the buildings. Where were the mines? Were they in the cave
itself? This was not copper ore. It was a partly refined product.

It was evident to John, and further verified that the entire chamber,
which was fully sixty feet long and fifty feet wide, was covered with a
layer of this copper for a height of six feet. A calculation of the
value could be readily made.

John and the boys made their way out and past the fires that were still
burning, and which would be relighted no more. The two absent ones were
not found. They had not returned. The reason was explained when the
village was reached. They were captured by Uraso before they had left
the cave a thousand feet.

During the day and the succeeding night the patients improved each hour.
Both of the invalid boys were able to sit up. Rogers wanted a full meal,
but still none were allowed to indulge. John announced that a start for
home