on of it. I can read you that";
and, taking a letter from his pocket, he read to Tom a geological
description of the hard rock.

"Hum! Yes," mused Tom, as he listened. "It seems to be of the nature of
obsidian."

"Bless my watch chain!" cried Mr. Damon. "What's that?"

"Obsidian is a volcanic rock--a sort of combination of glass and flint
for hardness," Tom explained. "It is brittle, black in color, and the
natives of the Admiralty Islands use it for tipping their spears with
which they slay victims for their cannibalistic feasts."

"Bless my--bless my ear-drums!" gasped Mr. Damon. "Cannibals!"

"Obsidian was also used by the ancient Mexicans to make knives and
daggers," Tom went on. "When Cortez conquered Mexico he found the
priests cutting the hearts from their living victims with knives made
from this volcanic glass-like rock, known as obsidian. It may be that
your brother has met with a vein of that in the tunnel," Tom said to
the contractor.

"Possibly," admitted Mr. Titus.

"In that case," Tom stated, "I may have to use a new kind of explosive.
That used for my giant cannon would merely crumble the hard rock for a
short distance."

"Then will you accept the contract, and help us out?" asked Mr. Titus
eagerly. "We will pay you well. Will you come to Peru and look over the
ground?"

"And kill two birds with one stone, and come with me also?" put in Mr.
Damon.

Tom pondered for a moment. He was about to answer when the tunnel
contractor, who was looking from the library window, suddenly jumped
from his chair crying:

"There he is again! Once more dogging me!"

As he rushed from the room, Tom and Mr. Damon had a glimpse of a face
at one of the low library windows--a face that had an evil look. It
disappeared as Mr. Titus ran from the room.

Chapter IV

Tom's Experiments

"Bless my looking glass, Tom, what does that mean?" exclaimed Mr.
Damon. "That face!"

"I don't know," answered the young inventor. "But the sight of some one
looking in here seemed to disturb Mr. Titus. We must follow him."

"Perhaps he saw your giant Koku looking in," suggested the odd, little
man who blessed everything he could think of. "The sight of his face,
to any one not knowing him, Tom, would be enough to cause fright."

"It wasn't Koku who looked in the window," said Tom, decidedly. "It was
some stranger. Come on."

The young inventor and Mr. Damon hurried out after the tunnel
contractor, who was running