Below them the searchlight showed a deep defile between rocky hills. And upon the sides of those hills there were leafless trees, with arms and branches and trunks as natural as life.

The wonderful chemical action of the water in these seas had doubtless caused a species of petrifaction. Astounded, the voyagers gazed upon the wonderful spectacle.

Wade was right in his element.

His hobby, his pet theory, had found verification. It only needed more extensive research to establish the fact of the complete isthmus.

For there was, of course, always the chance that this might be a part of the sunken Island of Mona. But Wade would not credit this.

“It is the isthmus,” he declared; “of that I am very sure. Now, to locate its coasts and contour. This can only be done by following it.”

So the Diver sailed slowly on, it being an easy matter to trace the line of the sunken shore.

“Which way shall we go first?” asked Frank. “To Cape San Antonio or to Cape Catoche?”

“To the last,” replied Wade; “then we’ll come back and make a sure thing of the lines.”

Over the deep defiles and rocky heights the submarine boat sailed slowly on.