thing," he added, as he
bent closer.

"But I can hear something!" added Nort.

"Hear something?" questioned Bud.

"Yes, the sound of running water down there. Listen!"

He bent with his ear over the crack in the rocks. And in the silence,
broken only by the slight movements of their ponies, from which they
had dismounted, the boys heard the murmur as of water flowing along far
under ground.

"I'm afraid that doesn't mean anything," said Bud when he had signified
that he, too, heard the ripple. "Dad said there were a lot of
underground streams around here. This one must come from the little
brook that flows through Smugglers' Glen. It takes a dip down under
the rocks and comes to the surface again farther on."

"I guess you're right," admitted Dick. "It doesn't mean anything. But
I didn't know there was underground water in this section."

"Oh, yes, plenty of it," Bud added. "I've seen other places with rock
fissures like this where you could hear water bubbling along beneath
the surface."

"Then this goes into the discard," spoke Nort, meaning that it was
useless to form any theory about the mysterious deaths if it was to be
based on the underground streams.

"But we'd better get on to the cave mine!" cried Bud. "If those
fellows are at their poison gas game again, it's likely that Sam
Tarbell and the fellows we left on guard are in as bad shape as these
cows. Darn the luck, anyhow!"

"That's what I say!" chimed in Nort as the three hastened to where they
had left their ponies. "Just as we thought we were sitting pretty,
with nothing to worry about, along comes this! Wonder how they worked
the game, anyhow?"

"They must have got back in the cave--probably from the end where they
ran out the time we chased 'em with our gas masks on," said Dick.
"They sneaked up on our fellows, let loose a cloud of gas, put them out
of business and then came down here to kill the cows."

"But that's what I can't understand," said Bud. "Why should they go to
the trouble of killing cows? Cows can't spy on those gold mine
jumpers. Cows can't get out any gold. It's all so useless, this
killing of our beasts."

"I guess they're just natural devils as Billee claims," suggested Nort.
"But we'll pay 'em back!"

"You bet we will!" exclaimed Bud. "And now to the rescue! We've got
to save Sam and his crowd if we can!"

They galloped their ponies in the direction of the Glen, and reached
the opening to the sinis