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.