“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, it is very strange,” agreed Harry, looking up.  Truth to tell, he had hardly been following the talk at all.  Harry Hazelton was quite content to be caught napping whenever Tom Reade had his eyes open.

“Now, I would like to go back to the mine and stay there until some time in the night,” Tom proposed.  “I would like to take Hazelton with me.  Soon we will arrange it, if necessary, so that Harry and I shall divide the time at the mine.  Whenever, in any of the tunnels, blank rock is struck, whichever one of us is in charge will stay by the blank rock blasting, keeping careful record, until pay ore is struck again.”

“You two young engineers are too infernally methodical,” grumbled Dr. Tisco under his breath.”

“That is a very excellent plan,” smiled Montez, amiably.  “We will put some such plan into operation as soon as we are fairly under way.  But not to-day.”

“I would like to start at once,” Tom insisted.

“Not to-day,” once more replied Don Luis, though without losing patience.  “Yet, if you are anxious to know how the blank rock is coming I can telephone the mine and get all the information within five minutes.  That will be an excellent idea.  I will do it now, in fact.”

Crossing the room, Don Luis rang and called for the mine.

“Our young engineers are very sharp—­especially Senor Reade,” murmured Dr. Tisco to himself, while the telephone conversation was going on in Spanish.  “Yet I wonder if our young engineer does not half suspect that Don Luis has no man at the other end of the wire?”

Tom did not suspect the telephone trick.  In fact, the young chief engineer had as yet no deep suspicion that Don Luis was a rogue at heart.

“The report is excellent,” called Don Luis, gayly, as he came back.  “In that tunnel where we saw the blasting done the blank rock has been penetrated, and the rich ore is coming again.”