voice so low that only Old Billee
heard.

"Take our lanterns," suggested Snake Purdee.

"And ropes," went on Bud. "We may need 'em!"

Accordingly the food and other supplies, which the searchers after the
secret of the underground water course had brought with them, were put
up on the ledge, and then they started down the black passage through
which the stream appeared to have branched, carrying Nort with it.
There was room but for one to walk at a time on this "bank," as it
might be called, of the hidden stream, and they had to proceed in
single file.

"I'd like to see a map of this place, so we'd know where we were
going," spoke Old Billee, as he swung his lantern from side to side in
an endeavor to disclose the hidden secrets of the place.

"I have an idea that the underground stream is shaped like the letter
T," spoke Bud. "The top, or cross stem, is the part that extends from
the river to our reservoir. We are now walking along the upright
piece."

"But if the main part of the T is also a stream, and the water is
running down that, as it is, instead of along the main stem, it becomes
for the time being a letter L, doesn't it?" asked Snake.

"Yes," assented Bud. "And as long as the water turns at right angles,
as it does at the place where Nort fell in, and as long as the water
runs along this same side passage, we don't get any at Flume Valley.
The letter T is in our favor, and L is against us."

"But we didn't see anything like this when we were here before,"
remarked Dick.

"Because we weren't on this side," Bud answered. "And I have an idea
that, in time, this second passage finally fills with water completely,
and when it does the stream again flows along the cross stem of the T
and we get it."

"Mebby you're right," Old Billee agreed. "But this isn't finding Nort."

"Will we--will we ever find him?" faltered Dick.

"Sure!" declared Bud, as heartily as he could.

But as they progressed in the darkness, stopping now and then to look
about by means of the light, calling again and again, and as no reply
came, even the heart of the stoutest of them sank in despair.

All they could see was black, rushing water, flowing in a channel it
appeared to have cut, after countless years, in the solid rock. There
was a narrow footpath, so to speak, on either side of this stream, and
it was along this the searchers were walking.

Suddenly Bud, who was in the lead, uttered a strange cry.

"What's the