“I have seen enough; let us go along.”

“All right,” agreed Frank. “A due west course is sure to bring us to Yucatan.”

“Very true,” agreed Wade, “but above all things go well armed and prepared for trouble. I feel sure that we have not seen the last of that schooner!”

The young inventor could not help a laugh at Wade’s earnestness.

“That is your bugbear,” he said. “How are they going to injure us at this depth of the sea? They have only the very crudest of diving-suits.”

“I don’t know,” replied Wade, “but I cannot help a feeling of that sort. I believe we have not seen the last of Poole.”

“It is a little curious that we have not as yet come to the sunken isle,” said Frank. “That I must regard as only a small part of the isthmus which did not sink in the first earthquake.”

“Beyond a doubt,” agreed Wade. “In that case we shall certainly come across it.”

“We will keep a lookout. It should be in about this latitude.”

The course they were pursuing was along the northern shore of the isthmus. It was easy to follow its conformation.