"What have you done?" gasped Dick.
"Search me!" answered Bud in such queer tones that Nort laughed.
And then a strange thing happened. As Nort struck another match he and the boys on the rock could see the water all about them beginning to recede. Slowly it flowed at first and then, with a rush, it began running out of the place as fast as it had run in.
"What's up over there?" called the voice of Old Billee from "shore," so to speak. "What you fellers doin' with th' water?"
"I just pulled that lever," sang out Bud.
"Then you've done the trick!" said the old cowboy. "You must have opened some gate, and the water's running away. Better swim over here while you have the chance. When the water comes back that rock may be covered!"
But another strange part of their mysterious adventures was that they did not have to swim back. For the water receded so rapidly that, in a little while, it was possible to wade from the rock to the stone edge of the pool where the other members of the party stood. And wade back to their friends Bud, Dick and Nort did.
"Oh, boy! But we're glad to see you!" cried Old Billee, as he caught Nort by the hand.
"You let out a mouthful that time!" declared Yellin' Kid, and his voice nearly split their ear drums, so magnified was it by the echoing, vaulted roof of the cavern.
"But what all happened?" asked Snake Purdee. "Is there some old Mexican grain mill under here that has a water-wheel, sluices and gates?"