"I believe I have," came the reply.
"And it has to do with this misty feeling in the air; has it?" continued the Kentucky boy.
"If my idea proves the right one, and I'm bound to find out before I go away from this place, it's got everything to do with it, Bob."
"Where there's smoke you'll find fire; and where there's mist I reckon water can be looked for," remarked Bob, quickly.
"Just so. Now Bob, have you ever been up in the Yellowstone Park region?"
"I can't say that I have, Frank."
"Then you see I've got the advantage over you; and that's what gave me a point in the game. Because I've stood and watched Old Faithful and the other great geysers play every half hour or so," Frank went on, as they slowly advanced into the passage which seemed possibly to act as one of many funnels through which the tremendous roaring sound was carried to the outside world.
"Geysers!" cried Bob. "Oh! now I get onto what you mean. You think, then, that in the heart of Thunder Mountain a giant geyser spouts every once in a while; and that as the water is dashed against the rocky walls it makes the ground shake. Is that it, Frank?"
"Yes," replied the other, "and the noise is so like thunder that when it is forced out through several queer, funnel-shaped openings like this one, it has puzzled the Indians for hundreds of years. Bob, more than that, I believe that every once in so many years, when an extra convulsion shakes things up here, the water bursts out through some passage, and rushes down that barranca in a wave perhaps twenty feet high."
"But they call it a cloud burst, Frank," suggested Bob.