"That's it," he said emphatically. "That must be it."
"What?" asked Jack.
"Why, there's a big level place just below the cave I was tellin' you 'bout. A plateau. Smooth as a floor."
The hum of the airplane had died away. The boys and their guide never had caught sight of the machine in the darkness.
Suddenly Frank pointed in the direction whence the sound of the airplane had come, ahead and slightly to the left.
"I thought I saw a light there," he whispered. "It was just a faint streak of orange. Now it's gone."
"Look here," said Bob to Tom Bodine, "does that cave face this way or is it on the other side of a hill?"
"It's on t'other side," answered Tom, "an' near the top."
"Well, I'll bet you there's somebody in that cave. And the light that Frank saw was some kind of a signal to the airplane."
The big ex-cowboy scratched his head.