done?" eagerly Bud asked.

"I don't know. But it's worth trying. You say you have gas masks?
They will be needed I think."

"Plenty of 'em!" cried Bud. "Come on back to the ranch where we still
have them. We may win yet!" he said to his cousins. "If the gold mine
peters out, as it has done, we'll get rich raising cattle in one of the
best valleys of the west--providing the poison gas can be done away
with."

"There's always an _if_ in the road," murmured Nort.

But when, a little later, the scientists, the boy ranchers and some of
the men, wearing gas masks, penetrated to the far end of the defile,
they found conditions which were distinctly encouraging. Professor
Dodson located the mass of mineral which, when wet, gave off the vapor
that caused death or disablement according to its strength.

"All that needs to be done," he said, indicating the stream which ran
for some distance in the open before plunging underground, "is to build
a small dam, change the course of this little river and send it down
_outside_ the defile, instead of _through_ it. Keep this stream
entirely in the open and you will do away with the poison gas. It is
really a not very difficult problem in engineering and irrigation. It
will not cost much to do this."

"Then it's going to be done, and it means the end of Death Valley
forever!" cried Bud. "I mean a happy ending," he added. "For we'll do
away with all danger."

"Thanks to you gentlemen and to Old Tosh," said Nort. "For he helped,
didn't he?"

"Indeed he did," agreed Professor Snath.

"And when the course of the stream is changed," went on his chief,
"there is no reason why the old herb doctor cannot resume work in his
cave if he wants to. It will be safe then."

"Guess he'll be glad to hear that!" chuckled Nort. "He's been like a
lost dog these last few weeks. Then those fellows, with their gas
tanks, didn't have anything to do with killing our cattle?" he
suggested.

"Not a thing," declared Professor Dodson. "It was a war against nature
you were fighting."

"We've only just begun to fight her!" cried Bud.

Mr. Merkel was not much disappointed when he learned that the cave mine
had petered out.

"I never took much stock in it," he told his son over the telephone.
"But I'm glad you've solved the mystery of Death Valley. I'll send
some engineers over, we'll change the course of that stream and go in
for cattle raising. That's our business, anyhow, not minin