"Look ahead! Look ahead! What is that—a river?"
"There is no river of size in this locality," declared the professor, quickly, training his glasses on the white streak that appeared on the ground ahead.
Phineas Roebach struggled forward to the operator's bench. He gasped:
"This is worse than I ever thought flying could be. Do you have to go so fast? I cannot get my breath. Hullo! That's the glacier ahead. The dog trail to Aleukan follows the ice for more than fifty miles."
"A glacier it is," agreed Professor Henderson. "It seems pretty smooth,
Jack. You can descend still farther."
That they were all suffering from the rarity of the atmosphere was plain. It seemed as though the envelope of breathable air surrounding the earth had suddenly become vastly rarified. If the atmosphere had been so changed all over the globe it would be a catastrophe unspeakable.
"We certainly can't cross these mountains—nor the Rockies," groaned
Jack. "How are we ever going to get home again?"
"If the air remains as it is now?" asked Mark. "You're right! We're imprisoned in this part of Alaska just as fast as though we were caged behind iron bars."
"If we only had some of those torches we used on the moon," said Jack.
"What will we do, Professor?" begged Mark.