“The river was here once,” said Uncle Tod, “but it’s gone now.”

“How can you tell it was here?” asked Chot.

“By the way the stones are worn,” was the answer. “See how smooth and rounded they are, where water has been flowing over them for years and years. But there is no water now, worse luck!”

The boys easily recognized the dry bed of some former stream—Lost River beyond all doubt. But where was Lost River now? That is what they wanted to know.

As Uncle Tod had said, the tunnel was much shorter than he had supposed. They had come not more than three miles under the mountain—a long enough passage if it had been dug by the hand of man for a railroad, as it was all through solid rock—but the rushing water which had, seemingly, bored the passage, took no note of time. It had centuries at its disposal, and had worn its way slowly.

Entering the tunnel at the camp, the explorers had wound their way through it, with the comparatively unimportant accidents I have described, and had emerged through a hole in the side of the mountain. All about them were water-worn stones, and they could trace where the stream had flowed downward from where they stood, but in the opposite direction from that in which they had been traveling. In other words they had walked against the direction of the stream.

“And that’s the queer part of it,” said Uncle Tod. “All along, boys, we’ve been going up grade through the tunnel, and that means the water of Lost River flowed down, just as it did before my mine went dry. Now we get here and at this point the course of the stream shows that the water must have flowed the other way, in the same direction we have been going.”

“You mean this hole here, where we just came out, is a sort of diving place,” suggested Rick.

“That’s it—a miniature watershed. Back of us, in the tunnel where we just came from, the water flowed east. Here it began and flowed west—that is when there was any water.

“So I can’t see,” went on Uncle Tod, “any use in keeping on. Lost River was here, but it’s gone. When it will come back—no one knows. Not much use waiting for it, I reckon. I don’t see why Sam and I didn’t find this out before, but he got frightened by a lot of queer noises in the tunnel, and wouldn’t keep on. I didn’t dare risk going alone, and we never got as far as here.