The cave was crossed by another underground stream, all of twenty feet wide, and flowing onward with tremendous swiftness.
It came out from under one rocky wall and disappeared under the wall opposite.
Taking a bit of driftwood, Dave threw it into the water, and it flashed out of sight instantly.
"I can't swim across that," he thought, dismally. "To attempt it would be foolhardy."
Now what was to be done?
He examined the walls carefully.
They were perfectly smooth, thus affording hold for neither foot nor hand.
"If the stream weren't quite so wide I might jump it," he reasoned. "But I—somebody is coming!"
He was right; somebody was entering the cave from the outer end.
The newcomers were two men, one dressed in the suit of an American business man and the other in the garb of a sailor.