did not want to make his chum nervous by confessing that he had
another reason for agreeing to remain there idle the balance of the
day, besides the fact of there being no hurry, and that they could take
notes just as easy there as farther up the mountain.

The fact was, he had concluded, it would be safer for them to remain in
hiding while daylight lasted, and do what searching they expected to
accomplish in the darkness of night.

It was too easy, for anyone who had no scruples, and wished to do them
injury, to drop a rock down from the wall of the canyon. Against this
sort of attack their rifles would be useless; and terrible damage might
result.

As to who would be guilty of such an outrage, Frank only remembered
that Peg was in a white heat of indignation, and fully capable of doing
some madcap prank in order to frighten off the two saddle boys. He was
also not a little worried about the rustlers, supposed to be lurking
somewhere not far distant.

Last, but not least, there were the prospectors to whom little Lopez
had admitted he was carrying the supplies that were secured on the pack
burro. Frank had not heard of any treasure-hunters having invaded the
slopes and valleys around Thunder Mountain; but this did not mean it
could not be true.

If these men were secretly taking out possibly large quantities of
precious ore, and did not wish to be discovered, or disturbed in their
operations, even they might try to alarm the invaders by hostile
demonstrations.

"It's as pretty a mixup as ever I heard tell of," Frank had said
several times that afternoon, while they were exchanging confidences in
connection with the remarkable possibilities around them. "What with
the rustlers, Peg and his crowd of thunder investigators, the little
Mex. boy and his unknown prospector bunch; and last but not least, Bob,
ourselves, it sure has me going some."

"Yes," the other had returned, "but I hope we'll keep clear of the
whole lot, and be able to find out something worth while. I wish the
next night was over, and we were galloping along over the plains headed
for good old Circle Ranch."

"Me too, Bob, always provided we carried with us an explanation for
those deep grumblings that shake the earth, and seem to come out of the
heart of Thunder Mountain. I'm a stubborn fellow, as I reckon you
know; and when I throw my hat into the ring I like to stick it through
till they carry me out."

"The same here," Bob had declar