g for shelter
from the storm, because Senor Peg wished it. I entered. Hardly had I
taken ten steps than something flew at me. I think it was a demon, for
it had sharp claws, and I thought I could smell brimstone and sulphur.
Just then the mountain yawned, and what with the terrible noise, and
having to fight off that unseen enemy, I climbed out of there fast, but
with all my fine clothes ruined. That was why I came down the side of
the mountain in such haste that I caught my foot. I thought that fury
was chasing me. Nothing in this wide world could tempt Spanish Joe to
go back there. The storm, it is a joke besides that terror of the
darkness!"

If he expected to alarm Frank, the Mexican cowman mistook the character
of the boy. Frank believed that the fellow's fears had made him
imagine more than half of what he declared had happened to him.

"Well, we leave you here, then, Joe," the boy remarked, sturdily;
"because we're going to find that cave, and see what lies inside it.
If you want to come along, all right; if not _adios_!"

He turned and started to climb, Bob tagging at his heels. But Spanish
Joe could not bring himself to accept the invitation. He looked after
the disappearing figures of the two saddle boys, and shook his head.

"No, not for Joe," he muttered. "He knows when he has had enough.
Money could not drive him to enter there again, and meet that unseen
thing. Out here the danger can be understood, but Joe he takes off his
hat to the young Senors; for grit they surely possess. _Adios_, Senor
Frank; but I doubt much whether we ever meet again."

But staunch of heart, Frank was leading the way upward, determined to
accept of the challenge which the cowboy's due seemed to throw at his
feet.

CHAPTER XVI

THE VENT HOLE IN THE WALL

The way grew rougher with every yard they traversed. How Spanish Joe
had come dashing down over this ground at headlong speed without
breaking his neck was a puzzle.

Frank was feeling his way along carefully when he heard Bob call his
name. The rattle of falling shale at the same time gave him a pretty
strong suspicion as to what had happened.

"Hello! what's the matter Bob?" he cried.

"I slipped, and fell over the edge of some sort of place here," came
back the answer. "Luckily I've managed to get hold of a rock and
stopped my tumble. But don't waste any time lending me a hand, Frank,
because it seems to me I feel the thing move. If another