itrogen."

"But where do they get the moisture?"

"That is another one of nature's great surprises, and shows how every
contingency seems to be provided for. I suppose you have both cultivated
corn--that is, have gone between the rows with a cultivator, and stirred
up the earth. You did this, as you were told, to keep down the weeds.
That was one reason, but it is not the principal one. A dry crust forms
over the surface of the ground, owing to the heat of the sun. When the
cultivator breaks up the crust the heat from the sun draws up the
moisture from below, and you are therefore watering your corn, and what
is more, you are breeding bacteria so as to supply food for the plants."

"After learning this I am glad we discovered the stone."

A more persistent search was now made, and George's "hole" was really
found to exist. It was just as he described it. Everywhere along the
hillside were rocks projecting out from the surface, but here was a
depression, or hole, fully fifteen feet square, with rocky sides, the
wall on the upper side of the hill being fully fifteen feet high,
whereas the lower margin of the hole had a wall not over four feet high,
so that it will be seen George had no difficulty in getting out after he
had recovered from his fall.

The Professor was in the hole in an instant. The growth about the
depression was so dense that it made the hole dark, but there was an
unmistakable odor of asphaltum. Some of the overhanging branches were
trimmed off, and every portion of the walls examined.

"What do you think made this? Was it washed out?"

"Some one dug this hole," was the Professor's response.

"What makes you think it was dug out?"

"There is plenty of evidence to show that. Look at the marks of tools on
the walls all about you."

"Do you suppose it was made to get oil?"

"No; but to get metals."

"What kinds, do you think?"

"Gold or silver; most likely silver."

"Do you think we have silver here?"

"Unquestionably; we have some samples of it at the Cataract now."

"When did you get it?"

"At the time we found the lead ore. Silver is usually a partner of lead,
and from my examination of the samples we have it is rich in silver. It
is likely that the indications of lead and silver all along this ridge
attracted the attention of a mining engineer, and this was a test hole
in prospecting for the ore."

"But if this hole was dug out, as you say, where did they put the dirt
and rock whi