On the beach he carefully scrutinized the sandy shore in search of some evidence of a small boat having been at this spot.

There was no evidence.

Barnes, however, said:

“It is doubtful if any tracks would be left, for the tide has risen since they have been here.”

The detective nodded.

“Nevertheless, I am sure that no small boat was here. If one had been some track would have survived the effacing action of the tide. But there is a stronger reason than that for being so sure.”

“What is it?”

“Have you used your eyes?”

“I think so.”

“Then you should know as well as I and require no telling.”