ent, then, when you are told that the footsteps abruptly
vanished at the summit of the zig-zag trail. Although dust lay thick
on the chambers within the mesa, not a solitary foot-mark marred its
soft gray surface. With the exception of the numerous footsteps on the
trail to the summit, there was no other sign of human visitors.

Like most old plainsmen and all wild animals, Pete was suspicious of
anything he couldn't understand, and it certainly did seem inexplicable
that a party of men should have visited the mesa and contented
themselves with running or walking up and down the causeway outside, or
promenading the summit. Such, however, appeared to be the only
explanation, and as such they were forced to accept it.

But such speculations as these were far from monopolizing the minds of
the professor and the boys. They eagerly traversed chamber after
chamber, finding these latter to be small "apartments," so to speak,
giving upon a common passage just beyond the "Council Hall." The
professor told them that each of these small chambers was formerly the
home of an aboriginal family. In the floor of the passage he pointed
to numerous bowl-like holes, which, according to him, had been used for
the sharpening of spears and arrow heads.

In some of the small chambers specimens of rude pottery were found, all
ornamented with the same figure of the human-headed rattlesnake.
Evidently the form represented must have been a deity of the tribe.
Each of the small chambers was lighted by one of the holes cut in the
face of the cliff, which they had noticed from below. The boys darted
in and out of the various rock chambers, like ferrets in a rabbit
warren, followed at a more leisurely pace by the professor and Coyote
Pete.

"Maybe we'll find some treasure," suggested Ralph Stetson, as, with
flushed faces, plentifully begrimed with dust, they paused in the last
of the rocky chambers.

"Say, you've got treasure on the brain, ever since we found that chest
of Jim Hicks' in the passage-way under the old mission, and started our
bank accounts," laughed Jack. "You must be forgetting that this mesa
has been visited frequently by cattlemen and wandering prospectors."

"Well, I should hardly call it frequently, Jack," put in Professor
Wintergreen, who was now standing with Coyote Pete at his elbow, in the
narrow entrance to the rocky chamber.

"Nope," added Coyote Pete; "you can bet your boots we didn't come here
except when w