Clay is impressionable. It will receive and hold the shape of an article which rests upon it a considerable time, and the detective argued that if the Shadow, as she was called, had at any moment rested upon the bottom at that particular point, she would have left her mark there. That she was a submarine, or at least was capable of diving beneath the surface and remaining there for some time, he had not a doubt. The very fact that she had approached the Goalong so silently that her proximity was not suspected was sufficiently satisfactory of that idea to him.
The water was, fortunately, unusually clear, and Nick had no difficulty in examining the bottom almost at his leisure. When he came to the surface again, and climbed up on the deck to a seat beside his friend, he remarked:
“Well, Max, it is as I thought. Your pirate craft is some sort of a submarine.”
“Is she? How do you know that? Have you seen her?”
“Well, not exactly.”
“I didn’t know but that was why you stayed under water so long. I thought maybe you had gone after her.”
“Well, you weren’t far wrong, at that. I figured that if she could dive, that was pretty nearly the explanation of how she approached you so silently, and, following up that idea, I decided that if she did dive, she must have left a mark of some kind on the bottom not far from that buoy.”
“And you found one, eh?”
“Yes, I found one.”