"All right, I'm ready to hear it," Frank remarked, laughingly. "Felix Oswald!" replied his father, quickly. The boy was indeed intensely surprised, if one could judge from his manner. "Your Uncle Felix, dad, who has been gone these three years, and whose mysterious disappearance set the whole scientific world guessing. And you say his name is there, signed to that paper found in the sealed bottle? Well, you sure have given me a surprise. Then he's still alive?" "He seemed to be when he wrote this," the cattleman said, reflectively; "but as he failed to put any date on it, we can only guess how long the bottle has been cruising down the Colorado, sucked into eddies that might hold it for weeks or months, until a rise in the river sent it forth again." "Say, doesn't that beat everything you ever heard of, Bob?" declared Frank, turning to his chum. "It certainly does," replied Bob, and then the ranchman's boy continued: "Perhaps you remember me telling you some things about this queer old uncle of dad's, Bob, and how, after he had made a name for himself, he suddenly vanished in a night, leaving word behind that he was going to study the biggest subject any man could ever tackle. And as he didn't want to be bothered, he said he would leave no address behind. They've looked for him all over Europe, Asia and Africa, but he was never heard from again. And now to think that he's sent word to dad; and in a sealed bottle too!" "That looks as if he must be somewhere on the Colorado River, don't it?" suggested Bob. "Undoubtedly," replied the stockman; "in fact, in this brief communication he admits that he is located somewhere along the Grand Canyon, in a place where travelers have as yet never penetrated. I can only guess that Uncle Felix must have been seized with a desire to unearth treasures that might tell the history of those strange old cliff dwellers, who occupied much of that country as long as eight hundred years ago. All he mentions about his hiding place is to call it Echo Cave. You never heard of such a place, did you, Mr. Hinchman; and you've lived on the lower river many years?" "I never did, Colonel," replied the man from Mohave City; "and perhaps few people have climbed through that wonderful gash in the surface of the Arizona desert as many times as I have." "In this brief note," continued Colonel Haywood, "Uncle Felix simply says that he has become aware of the passage of time; and since his labors are not yet completed, and he does not wish to allow his friends to believe him dead, he has concluded to communicate with me, his nephew. And as he knew of no other way of doing so, he resorted to the artifice of the floating bottle." "Mighty considerate of him, that's sure," chuckled Frank. "Been gone now two or three years, and suddenly remembers that there are people who might worry about his dropping out of sight."