"Will it be safe?" asked Ruth.
"Oh, surely. Why, we have to go in it when we make the moving picture, so we might as well get used to it. They say this ice lasts nearly all summer. It's down in a deep hollow, you see. Come on in."
"Go ahead! I'm game!" Paul said, grimly.
The girls hesitated, but only for a moment. Then they followed the young men into the cavern.
The entrance was rather small, and they had to stoop to get through it, but once inside the cave widened out until there was room for perhaps a dozen persons.
"What a lovely place for a dance!" cried Alice, as she slid about. "It's so slippery that you'd need those new slippers with rubber set in the sole. Come, on, try a hesitation waltz," she cried gaily to Ruth.
Paul whistled one of the latest popular airs, and Ruth and Alice slid about.
"Come on!" cried Paul to Russ. "I'm getting the craze, too."
The two young men danced together a moment, and then came an interruption that caused them all to look at one another.
There was a grinding, crashing sound outside, and the next moment the entrance to the cave was darkened.