The detective really wished to examine the bottom of the cove. The idea did not occur to him because he believed that he would discover any suggestive trace of the pirate down there, but he put the thought into words because it was his professional habit never to neglect even the most trivial and apparently unimportant item from his investigations.
The idea of examining the bottom of the Sound for traces of a vessel which had passed over that spot would be absurdly ludicrous; but, all the same, there was one idea which had been suggested to Nick by the description Kane had given him of the pirate craft, and he believed it to be more than possible that there might be an indication of the fact—if it were a fact—to be found at the bottom, not far from the buoy to which the yacht was moored.
It will be remembered that he asked Kane if he thought the pirate craft was a submarine, and it must be recorded that, notwithstanding the reply he received, he thought it more than probable that the silent approach of the vessel had been accomplished in that way.
Nick knew that the bottom of that cove was soft, and largely composed of clay, especially at points where it attained as great a depth as that where the yacht was moored.
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?”
“I didn’t know but that was why you stayed under water so long. I thought maybe you had gone after her.”