The scientist nodded his head.

“Yes,” he said, “I am satisfied. Let us go back.”

Frank was glad to lead the way out again into the street. They then turned their footsteps toward the submarine boat.

Barney and Pomp were waiting for them. Straight to the gangway they came.

In a few moments they were safe in the cabin once more. The trip had been a success.

But Wade was still looking ahead, and was anxious to continue on his way along the isthmus.

So the Diver arose and headed for awhile over the sunken city. Then it left it behind.

The presence of the sunken city settled a number of facts. It was true beyond peradventure that there had once been an isthmus between Capes San Antonio and Catoche.

It was also certain that there had once dwelt upon it a race of people of great intelligence. That the sea had wiped all out of existence was certain.

Wade studied the matter thoroughly and most scientifically. So he said to Frank: