"An underground stream," said Professor Dodson. "They are not uncommon in this region. But——"
Suddenly he started back and withdrew his face quickly from above the crack in the earth.
"Hurry away from here!" he cried. "The gas is rising. I begin to understand now. It is the secret you have been trying to solve. Hurry away! It may not be deadly, but it will overcome all of us in a short time."
He ran down the defile, away from the long fissure, followed by the others, Billee and his men driving the ponies before them. Professor Dodson had made a strange discovery, after Old Tosh had put him on the track of it.
CHAPTER XXV
THE END OF DEATH VALLEY
Hurrying along, some of the men in their saddles, others stumbling on foot, not having taken the time to mount, the whole party rushed out of the defile. It was not until they had reached open country, some distance removed from the entrance to Smugglers' Glen, that the older scientist thought it safe to call a halt. And he did not do this until he had looked around, with his assistant, to make sure there were no earth fissures near, and had also ascertained the direction of the wind. He tested the air by breathing deeply of it and said:
"We're safe for a time. But there's no telling how long. This is a most remarkable natural phenomenon—one of the most remarkable I have ever happened upon."
"Very remarkable," agreed Professor Snath.
"But what's it all about?" asked Bud. "We've seen those earth cracks before."