feet.

"Look out now!" cried Tom, suddenly. "If things go right there won't be
a rock left for you to 'bash' anybody's head with, Rad. Look out!"

The three cowered inside the shack, which, though it was rudely made,
was built of heavy logs and planks, with a fronting of sod and bags of
sand.

Tom turned a switch. There was a loud report, and where the stone pile
had been there was a big hole in the ground, while the air was filled
with fragments of rock and dirt. These came down in a shower on the
roof of the shack, and Eradicate covered his ears with his trembling
hands.

"Am--am de world comin' to de end, Massa Tom?" he asked. "Am dat
Gabriel's trump I done heah?"

"No, you dear old goose!" laughed the young inventor. "That was just a
charge of my new explosive--a small charge, too. But it seems to have
done the work."

He ran from the shack to the place where the rock pile had been, and
picked up several small fragments.

"Busted all to pieces!" exulted Tom Swift. "Not a piece left as big as
a hickory nut. That's going some! I've got the right mixture at last.
If an ounce did that, a few hundred pounds ought to knock that Andes
tunnel through the mountain in no time. I'll telegraph to Mr. Titus."

Leaving Koku and Rad to collect the wires and firing apparatus, there
being no danger now, as no explosive was left in the shack, Tom made
his way back to the house. His father met him.

"Well, Tom," he asked, "another failure?"

"No, Dad! Success! This time I turned the trick. I seem to have gotten
just the right mixture. Look, these are some of the pieces left from
the big rock--one of the samples Mr. Titus sent me. It was all cracked
up as small as this," and he held out the fragments he had picked up in
the field.

Mr. Swift regarded them for a few moments.

"That's better, Tom," he said. "I didn't think you could get an
explosive that would successfully shatter that hard rock, but you seem
to have done it. Have you the formula all worked out?"

"All worked out, Dad. I only made a small quantity, but the same
proportions will hold good for the larger amounts. I'm going to start
in and make it now. And then--Ho! for Peru!"

Tom struck an attitude, such as some old discoverer might have assumed,
and then he hurried into the house to telephone a telegram to the
Shopton office. The message was to Mr. Titus, and read:

"Explosive success. Start making it at once. Ready for Peru in month's
time."