s that grew against the base
of the cliff.

"Well, I declare, there it is for a fact!" exclaimed Bob, as he saw a
rough opening before him, which came almost together five feet from the
ground, leaving only a dark, uneven, slanting line that crawled up the
face of the cliff like the photograph of a zigzag bolt of lightning
taken with a snapshot camera.

"There you are," said Frank, with a broad smile. "Unless all signs fail,
here's the entrance to the mysterious Echo Cave. We have been more than
lucky to find it with so little trouble."

"Just to think of it," remarked Bob, as he bent over to look up into the
gap as well as he was able; "here's where the queer old Professor has
been hiding for all this time, and no one any the wiser. But Frank,
however in the wide world do you suppose he found out the way to get up
there?"

"We would have found it sooner or later, even if Charley Moi had not
seen the old Indian moving along," replied Frank, with the confidence of
one who knows what he is talking about.

"Y--yes, I reckon we would, after you'd prowled around a little, and had
some chance to look the ground over. Then you believe he must have found
the presence of those windows looking out of the cliff just like we did;
by using a powerful glass? And, thinking that here was the very place
for him to hide and study, he set about looking for the road up, and
found it, very likely."

"He did it by using common sense, and applying all he knew about the
ways of these people of the long ago," replied Frank. "And you can see
that if he chose, he could have thrown that bottle out of one of the
openings up there, so that it would drop in the passing current of the
Colorado, to be carried down-stream until somebody saw it; and finding
the message to my father, sent or carried it to Circle Ranch."

"Well," observed Bob, with a gleam in his eye, "now that we've found a
way to get up to Echo Cave, have we the nerve to start in?"

CHAPTER XIX

FORTUNE STILL FAVORS THE BRAVE

Instead of replying at once to this question, as Bob undoubtedly thought
his chum would do, Frank seemed to give a start. He dropped to his hands
and knees, and seemed to be examining some marks on the ground.

If ever the fair knowledge of reading tracks which Frank possessed was
called upon to do duty, it was now. Bob, of course, could not understand
what possessed his comrade; but simply stood there and stared, wondering
what Frank had foun