We were nearly ready to come out, when I took a dive from a post on the end of the wharf, and then turned, under water, to swim in shore.

I intended to try to keep under until I got into water shallow enough for me to touch bottom, and walk ashore.

After half a dozen strokes, I felt for the bottom and my feet touched it.

Then I raised my head, but I didn't raise it out of the water.

It struck something hard.
In an instant I knew what had happened.