he rope nearest him. If he had not been in such a hurry, he
would have seen that the other should have been severed first. As it
was, he had cut the one that held the boat's bow to the stream.
Instantly the flat-bottomed craft swung dizzily around, and still held
by her stern mooring, dashed against the bank.

For a minute the boys feared she was stove in, but there was no time to
waste on an examination.

Slash!

One stroke of the knife severed the remaining rope, already drawn as
taut as a piano wire. But, as Jack's knife fell, the place became
filled with shouts and confusion.

Ramon had been a little in advance of his men, and now they were all in
the place. A second's glance showed them what had happened. Not only
were the boys about to escape, but if they did not stop them the secret
of their underground route across the border would be discovered, and
its usefulness at an end.

No wonder they strained every nerve to reach the boys. Ramon himself
had bounded to the side of the subterranean river as the boat swung
round. As her gunwale had struck the bank, he had leaped aboard. But
before he could use his revolver, Walt's powerful arm knocked the
weapon out of his hand, and it fell on the bottom of the boat. With a
snarl of rage, Ramon flashed round on the boy. But whatever the
Mexican might have been able to do with knife or pistol, he was no
match for the muscles of the American lad.

Walt fairly picked the lithe form of the gun-runner from the floor of
the boat as Jack's knife fell across the remaining rope. With a splash
and a loud cry, Ramon pitched overside into the stream. As he fell,
though, he managed to clutch the side of the craft and he hung on,
desperately endeavoring to draw himself up into the boat.

His followers, seeing what had happened, rushed down on them. A
tempest of bullets rattled about the boys' heads as they felt the rope
part. It was no moment for sentimental hesitation. Walt raised his
foot, and the next instant brought his heavy boot down with crushing
force on Ramon's clinging fingers.

With a yelp of pain, the fellow let go and was rolled over and over in
the river, while half a dozen of his men waded in to rescue him.

"Yip-ee-ee-ee! We're off!" yelled Jack, with a true cowboy yell. The
lad was carried away by the excitement and thrill of the adventure.

With a lurch and a bump, the frail craft carrying our three young
friends shot forward. The lamp-lit