Guesses On What This Is?

[Uncle Jesse]

It's junk. That's what it is.

You are entitled to your opinion, but if you see junk you are taking a very narrow vision. In my opinion, it is a relic of times long ago, probably a key piece that made the production of lumber possible using the power of a small stream. When they moved the rest of the mill it was probably too heavy to handle with the men and equipment available at the time and for whatever reason the owner never returned to claim it. It was probably relatively expensive there are machined steel shafts of considerable size, around 2.5 inches I would guess and two machined plates which were possibly cast iron, maybe steel. I have never had the opportunity of visiting that part of the world, but I would guess there are probably building still around where the lumber was sawn on that mill. Of course, it could have been a grist mill, then there's a different story and list of things that happened.