having been discovered.

Boom!

Over by the ridge where Gage and his fellow rascals lay it looked
as though a volcano had started in operation on a small scale.

Fragments of rock, clouds of dirt, splinters and bits of brush
shot up in the air.

Following the report came a volley of terrific yells from Dolph
and his fellows.

They had been on the instant of firing when the big explosion
came. Jim Ferrers, too, was taking careful aim at the moment.

It is a law of Nature that whatever goes up debris, mixed with
larger pieces of rock and clots of earth, descended on the scene
of the explosion. Yet little of this flying stuff reached Dolph
Gage and his companions, for they were up and running despite
the mark that they thus presented to Ferrers.

Nor did the rascals stop running until they had reached distant cover.

"Stop it, Jim---don't shoot!" gasped Tom Reade, choking with laughter,
as Ferrers leaped to his feet, taking aim after the fugitives.

"I want Dolph Gage, while I've got a good, legal excuse," growled
Ferrers, glancing along rifle barrel at the forward sight.

"Don't think of shooting," panted Tom, darting forward and laying
a hand on the rifle barrel to spoil the guide's aim. "Jim, it
isn't sportsmanlike to shoot a fleeing enemy in the back! Fight
fair and square, Jim---if you must fight."

There was much in this to appeal to the guide's sense of honor and
fair play. Though scowled, he lowered the rifle.

"Tom, you everlasting joker, what happened?" demanded Harry Hazelton.

"You saw for yourself, didn't you?" retorted Reade.

"Yes; but-----"

"Are you so little of an engineer that you don't know a _mine_
when you see one, Harry?"

"But how did that mine come to be there?"

"I planted it."

"When?"

"Today, when you started on your ride."

"Oh!"

"You see, Harry, I was pondering away over mining problems this
morning. As you had the only horse, that was all that there was
left for me to do. Now, you must have noticed that most of the
outcropping rock around here is of a very refractory kind?"

"Yes," nodded Hazelton.

"Then, of course, you realize that for at least a hundred feet down
in the mine the rock that would be found would be the same."

"Undoubtedly."

"So, Harry, I was figuring on a way to blast ore rock out whenever
we should find refractory stuff down a shaft or in the galleries
or tunnels of a mine."

"Fine, isn't it?" retorted Hazelton. "A great sche