He gaped upward at the bare-faced wall that arose for hundreds of feet, without any particular ledge or outcropping where even a nimble Indian could find safe lodgment for his moccasined feet. "But, Frank, however could the old Moqui get up there to see Uncle Felix?" he asked. "D'ye suppose he made some sort of signal, and the hermit lowered a long rope with a noose at the end, which would draw him up? Wow! excuse me from ever trying to fly in that way! It would make me so dizzy I'd be sure to drop, and get smashed." "You're beating on the wrong track, Bob," remarked the other. "No rope could be lowered all that distance; and even if it could no one man would be able to pull another all the way up." "But there must be some way of getting to the place where the slits in the face of the cliff tell of windows. However do you think he did it, Frank?" "Just because you don't happen to see a ladder, Bob, is no evidence there isn't a way to mount upward. One thing about this great cliff I guess you didn't happen to notice. That shows you pass things by. Look again, and you'll see that it seems to have been split by some volcanic smash, ages ago. There's a regular crevice running slantingly up the face of the rock. You see it now, don't you?" "Sure I do; and I was blind not to take notice of the same before," Bob replied. "Fact is, I did see that uneven mark, but just thought it was a fault in the make of the cliff, as a miner would say." "Well, that crack extends four-fifths of the way up to the top; and far enough to reach the place where we noticed all those dark marks, which we believed must be windows of the many rooms or houses of the cliff dwellers. Get that, Bob?" "Sure I do, Frank, and after your explanation I can see what you're aiming at. But where does that ragged crevice start from down here, do you think?" Frank stepped forward. Just as if he had it all figured out, he bent down, and with his hand drew aside the bushes 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.