“That is true,” he cried. “It is a river, as I live!”

At once an idea seized Frank.

He started back for the shore.

“Where are you going?” asked Roger, in surprise.

“Back to the boat.”

“What for?”

“I’ll tell you when we get there.”

Roger said no more.

He followed Frank to the shore and got into the boat.

They rowed back to the Explorer and clambered aboard.