Reade responded. "I want to know what the chances are, as based
on the record of the mine to date. Of course, Don Luis, you know
what it means, often, when pay ore fails to come out of a streak,
and a solid wall of blank rock is encountered."

By "blank rock" Tom meant rock that did not contain a promising
or paying amount of metal in the ore.

"What it means?" Montez asked. "No; I can't say that I do."

"The wall of blank rock, found at the end of a vein of gold, Don
Luis, often, if not usually, means that the vein has run out,
and that it is useless to dig further."

"I did not know that," murmured the Mexican, in a tone of merely
polite astonishment. "Then you believe that _El Sombrero_ will
not turn out much more profitable ore?"

"I didn't say that," Tom continued. "But I will admit that finding
the wall of blank rock ahead made me a bit nervous. Some great
mines have been started, Don Luis, as you must be aware. For
a few weeks they have panned out ore of the highest value. Much
capital has been put into such mines, and for a time men have
thought they owned a new Golconda. Then--suddenly--the blank
wall, and no more gold has ever come out of that mine. In other
words, it was but a pocket of rich gold that had been struck, and
nothing more. Hundreds of men have ruined themselves by investing
in such mines."

"I see," murmured Don Luis, thoughtfully.

"You did not know this before?" Tom asked, in some amazement.

"No, Senor Tomaso. I have been a good business man, I suppose,
for I have prospered; and much of my money has been made in mining.
Yet I have never had the assurance to consider myself a practical
mining man. Dr. Tisco, here, is--"

"An ignoramus on the subject of mining," declared the secretary,
who appeared just then to wake up.

"Carlos is modest," laughed Don Luis. "True, he is not a skilled
mining man, yet he knows so much on the subject that, compared
with him, I am an ignoramus. But that is what you are here for,
you two. You are the experts. Investigate, and then instruct
us."

"Have you any record of the number of times that you have encountered
the blank rock, and the number of feet in thickness of the wall in
each case?" Tom asked.

"Oh, no."

"That is unfortunate," said Reade, thoughtfully. "Hereafter we
will keep such a record carefully. Don Luis, I will admit that
I am perplexed and worried over this blank rock problem. I know
Hazelton is, too."

"Yes,