It’s definitely rotten. It’s very fragile. Every time I pick it up, I have to be careful not to crush it further. It feels like rotted wood.

I just looked up teredo. Wow that is one nasty critter. I assume it’s fairly well controlled, or I would have learned about it a long time ago. And the photo in Wikipedia looks exactly like what I have. Plus, not shown in the photos I took is the center. There is some sort of bolt hole that passes through and it looks like there’s tar around it. I read that creosote is what they use to protect against this scourge. Looks like it didn’t work completely in this case. Although the small area around the hole/tar is intact.

Losing fingers since 1969