“It is good enough ore,” Montez replied, with a polite shrug of the shoulders.

“Now, from the second tunnel that we entered, and where we also found a pile of loose ore, here is another sample.  It is as rich as the first sample.”

“Certainly, Senor Tomaso.”

“But in this second tunnel I had a drilling made and a blast fired.  Here,” picking up a third envelope and emptying it, “is a sample of the ore that we saw taken from that blast.  If this sample contains any gold or silver the quantity is so small, evidently, as to render this kind of ore worthless.”

“Yes?” murmured Don Luis, softly.  “What is it that you have to say?”

“Why, sir, how does it happen that, right on top of such extra-fine ore we run upon blank rock at the very next blasting.”

“That sometimes happens in El Sombrero,” Don Luis replied, smoothly,

“How often has it happened?” asked Tom, looking up from the table and glancing keenly at Don Luis.

Dr. Tisco, though he appeared to be almost asleep, stirred uneasily.

“How often has it happened?” repeated Don Luis.  “Oh, perhaps a dozen times in a few months, taking all the tunnels together.”

“How long have these streaks of blank rock been?” insisted Tom Reade, while Harry wondered at what his chum was driving.

“How long?” echoed Montez, with a shrug of his shoulders.  “Oh, how should I know?  Personally I am not interested in such things.”

“But have you gone as much as a whole week drilling and blasting through blank rock?” Tom pressed.

“A week?  No; not for two days.  Of that I am certain.  But why do you ask all this, Senor Tomaso?”

“In order that I may better understand the nature of the mine,” 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.”