ried up. However,
it didn't cave in, except in a few places, and we now use it to bring
water to Flume Valley. There is really only a comparatively short
length of pipe at either end, one end being where the water from the
Pocut River enters, and the other where the pipe delivers the water to
our reservoir."

"How are you going to find the break?" asked Dick.

"Or stoppage?" suggested Nort.

"Well, I aim to ride over the mountain tonight," answered Bud, "and see
if all is clear at the river intake end of the line. If it is, I'll
know there must be a stoppage, or break, somewhere inside the old water
tunnel."

"How you going to find that?" inquired Nort.

"Why, we'll get lanterns and ride through," replied Bud. "That's easy!"

"Ride through an underground river!" cried Dick. "You can't!"

"No, we couldn't if the old underground river course was _full_,"
agreed Bud, "but it _isn't_. There's only a comparatively small amount
of water flowing through the old course, which is wide enough for two
of us to ride or walk abreast, and twice as high as you need. I've
ridden through more than once. It's like a long, natural tunnel under
the mountain, with water flowing in the center depression, so to speak."

"Must be rather spooky inside there," suggested Nort.

"It is a little; and it's nearly an all-day's ride. But it's the only
way to find the trouble. Professor Wright said that some day the water
might work through, and go off on a new course, and in that case I'd be
dished until I could stop up the break."

"Well, we'll help all we can," offered Nort.

"Sure thing!" echoed his brother.

"We'd better take it a bit easy now," spoke Bud, as the ascent of the
mountain became more steep. "We don't want to wind the ponies, and we
may have a hard day ahead of us to-morrow."

"It _is_ quite a climb," admitted Nort. "Are we going to ride all
night?"

"No, we'll turn in about midnight," said Bud. "But this will give us a
start so we can get to the Pocut River end of the flume by morning. We
can stop any time you fellows want to."

"Oh, we aren't tired!" Dick hastened to say, a sentiment with which his
brother agreed. "This is as much fun as riding herd, and driving off
the cattle rustlers."

"Glad you like it," commented Bud. "And the rustlers might as well
drive off our stock, if we don't soon get this water to running again.
Old Billee said I'd have bad luck when that black rabbit crossed my
path,