"Then we'll have to swim back where Nort is," Bud answered.

"Shucks! You won't have to do nothin' of the sort!" declared Old Billee stoutly. "She won't come up any farther than it did before!"

And he was right. When the water around the rock lapped the erosion mark, which had been worn in the hard stone by centuries of the flow of the fluid, the flood ceased. The roaring, bubbling and seething, like that which takes place in a ca.n.a.l lock, came to an end, and the water of the pool became quiet.

"There! What'd I tell you?" cried Old Billee. "I closed th' water gate, that Bud opened to let th' water out, an' she come back. Now all we have t' do, so we can walk back, is t' yank this lever again."

"Does it only work two ways?" asked Yellin' Kid, his voice again softened, as the mystery of the place seemed to cast a shadow over him and the others.

"Seems to," Bud answered, holding his lantern down close to where the copper handle entered the rock.

There appeared to be a slot cut in the hard stone--a slot about three inches wide, and a foot long, in which the copper lever could be moved backward and forward, but not from side to side.

"Let's try the other way, now," suggested d.i.c.k.

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 d.i.c.k.

"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 d.i.c.k. "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 d.i.c.k.

"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 d.i.c.k.

"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 d.i.c.k.

"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 explained.

"Why wouldn't it be there?" Old Billee wanted to know. "Do you think them Hatchet-texts have sneaked in and took it?"

"You mean Aztecs?" laughed Yellin' Kid. "No, I wasn't referrin' to them. I mean I hope our monkeyin' with that copper handle didn't send the flood over the place where we left our things."

"I never thought of that," said Bud. "By Zip Foster! I hope nothing like that _has_ happened!"

With anxious hearts they hastened back to the place where Nort had been swept away. They had left the strange lever set to drain the pool, and what state of affairs they would find on returning to their point of digression no one could say.

"Maybe we'll find the water running on into Flume Valley," suggested Nort, who seemed to be almost himself again, except for a feeling of weakness.

"I hope so," spoke Bud.

But this was not the case. On reaching the place where the tunnel branched, they found no water there at all. None was running in the main channel, and none was turning off down the "stem of the T," to use the ill.u.s.tration I first employed.

"Keeps on being strange, doesn't it!" said Bud.

They all agreed with him.

"What's the next move?" asked d.i.c.k, as they gazed about, finding their food and supplies safe, and no water, to mention, anywhere about.

"Let's grub!" suggested Snake.

"And make a fire and heat the coffee," urged Bud. "I don't believe the smoke will do any harm, and there's plenty of dry driftwood in the higher places, and on little ledges."

"Some hot coffee would go down mighty well!" remarked Nort.

"Then you're going to have it!" a.s.serted his cousin. They had brought some of the cold beverage along in tin flasks, and these were soon heating over a little blaze that was kindled along the bank of the underground stream that was again dry.

The food and hot drink put new hearts into all of them, especially Nort, and when appet.i.tes were appeased they gathered about the cheerful, if small, blaze, which gave off scarcely any smoke, and held a discussion.

"What I think we had better do," said Bud, "is to travel on until we come to the place--if such a place there is--where this stream again shunts off to the side. For I'm sure there is such a place if we find that the water is running into the tunnel from the river."

"We can't be sure of that, though," Old Billee said.

"No, but we can find out when we get to the other end of the tunnel,"

declared Bud. "My idea is--though, of course, I might be wrong--that there are two side pa.s.sages, so to speak. Sometimes the water branches off the main channel and fills the pool where we found Nort on the rock. Then it may flow down another channel, farther on, but nearer to the river end of the tunnel."

"But if the water came along the main channel, until it got here, and then filled the pool to the limit, as was evidently the case,"

suggested Nort, "why wouldn't the water then back up and go on to our reservoir--and it didn't do that."

"There may be some outlet from that pool and cavern where we were,"

said Bud.

They considered this for a moment, and agreed that he might be right.

"Then what we've got to look for," went on Bud, "is another side pa.s.sage where the water is shunted off, that is, providing it is not cut off at the river pipe. And if there is such a pa.s.sage it must be on the right-hand side of the stream, as was the one where Nort fell in. For we went all along the left-hand bank the other time, and didn't discover anything."