"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.
"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[p. 220] 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.