d time and again by
curious folks hoping to discover some treasure, or keepsakes of the
extinct people. No chance for the old professor to hide away there."

"But pretty soon we're going to discover a new batch of those caves in
the face of the rock, something unknown to all other searchers. We'll
find it by the aid of this same glass; and because we're looking for it,
high up. In all these other cases you see, Bob, there were shelves of
rock above shelves; and new ladders have been made by the guides, so
that anybody with nerve could climb up and up. Now these ladders give
the thing away. And I've somehow got the notion in my head that in the
case of the rock dwellings where the professor is hiding himself, there
is no outward sign in the shape of ladders."

"But in that case, Frank, how under the sun could the old fellows ever
get up to their dens, which you said must be near the top of a high
cliff?"

"Well, that's something we're going to find out later on, you see,"
replied the other, serenely. "Perhaps they had some way of lowering
themselves from the top by means of a rope, or a stout, wide grape vine.
Then, again, there may be some cleft in the rock farther away, that no
one would notice; but which was used as a trail, running up into the
cliff, and to the rock houses."

"It does take you to figure out these things," declared Bob, in
admiration, as they trudged along, with Charley Moi in advance.

"Then we haven't yet got to the place where the Chinese buyer meets his
employer with the eatables?" Bob remarked after a little silence.

"The last time I asked him he kept saying it was only a little farther
along," replied Frank.

"There, look at him stopping right now; and Frank, he's grinning at us
in a way that can only mean one thing. That must be where he always
waits for the queer old gentleman to show up."

"How about that, Charley; is this the place where you hang out?" asked
Frank, as they hastened to join the guide.

"Allee samee place," replied Charley Moi, waving his yellow hand around
him. "Not know where shaib come fromee, always turn roundee rock," and
he pointed to a large outlying mass that had, ages ago, become detached
from the towering cliff overhead, and fallen in such a fashion as to
partly obstruct the canyon trail.

Frank looked around him eagerly.

"We must be getting warmer all the time," he remarked; "and if you just
take a look at that river right now, you'll see that up yond