nd forward, but not from side to side.

"Let's try the other way, now," suggested Dick.

Once again Old Billee pulled on the copper shaft, which, as they could
see by the light of all their lanterns combined, seemed to have been
rudely hammered out, for it bore the rough marks of a primitive forge.

And no sooner had the lever been pulled to its limit in the slot than
there sounded again the rushing, roaring tumult of noises, and, after a
little, the water began receding once more.

"We've discovered the secret!" cried Dick.

"No, only part of it," said Bud. "We've got to find where the water
goes, and if pulling this lever sends it into our reservoir. That's
the main thing to discover."

"But we're on the track of part of it," went on Dick. "I wonder who
built this secret water gate, and the lever that operates it?"

"It may be part of the work of the ancient Mexicans, the old Indians or
the Aztecs, who inhabited this land ages ago," said Bud. "Copper will
last almost forever, you know, even in water, as it doesn't rust. And
you've read how the ancient Aztecs used to build great vaults under the
mountain, and arrange to flood them to keep their gold away from the
Spaniards."

"Yes, I've read of that," admitted Dick.

"Say, where can you get a book like that?" demanded Old Billee.

"I've got one at the camp," Bud answered. "I'll let you take it. Of
course my theory may be all wrong," he went on. "But I begin to
believe we've stumbled on some ancient Aztec water system."

"You don't mean to say those old Mexicans, for that's what the Aztecs
were, are still hanging around in this cave, turning your water on and
off, do you?" demanded Dick.

"No, it's some one more modern who's making trouble for us," Bud
declared. "But we're on the track of a big discovery, I believe.
Look, the water is almost gone!"

This was true. The pool was emptying itself as it had done before,
and, in a short time they could walk back to where Nort awaited them.

"What's the next thing to do?" asked Dick.

"Get back where we left our grub and feed our faces," suggested Snake
Purdee.

"Yes, I think that will be best," Bud said. "Then we can talk over the
next move. I begin to feel hungry."

"I hope we won't be disappointed," remarked Yellin' Kid and his vocal
powers seemed to be on the mend, for he called loudly.

"Disappointed? How?" asked Old Billee.

"I mean I hope we find our grub where we left it," Kid explai