"But we reached here just in time!" declared Old Billee. "Now let's get t' th' bottom of this. We know there's a main stream, an' two branching streams. One of th' branching streams is controlled by th' water gate with th' copper handle."
"And there must be another gate here, or else Del Pinzo and his crowd couldn't have shut off the water as they did before they ran away," went on Bud. "There must be a whole maze of water-courses in this old tunnel. Probably the Aztecs dug 'em to save their gold and other valuables. But I'd like to know what that roaring is?" and as Bud and the others listened they could hear a subdued murmur, a rumbling and roaring sound, that seemed to shake the whole tunnel near where they stood.
"Maybe this leads to it," suggested Dick, as he walked along and suddenly flashed his lantern across another opening—a natural stairway leading down into black depths.
"Let's try it," said Bud.
Down it they went, one at a time, carrying their lanterns. And as they advanced, descending until they came to a level passage, the murmur and roaring became louder.
"Would you look at that!" suddenly cried. Bud, in an awe-stricken voice, as he came to a stop and pointed ahead.
And then, as the others gathered about him and looked, they saw a wondrous sight.
They had entered a cavern, similar to the one where Nort had been found, but not so large. And from the very centre, it appeared, of the uneven rocky floor of the cave there spouted out a stream of water about three inches in diameter.
Solid white was this stream of water, like a bar of glass, and it shot out of a round hole in the floor as a stream comes from the nozzle of a fire hose. It was inclined at an angle of about forty-five degrees, was this strange stream of water, and whence it came and whither it went to the boys and their friends could only guess.
It was this powerful, rushing stream, under immense head and power it seemed, that caused the rumbling, roaring sound. It appeared to strike against some rocky wall a long distance off, so far that the light of the lanterns could not penetrate to it, and the searchers did not feel like venturing beyond the point where the terrific stream issued.