Old painting on slate - where do I find value?

I've had this since about 1978 when I had an antique store. At this point, my kids have convinced me they don't want my 'stuff' and I should start downsizing and use the money for ourselves to travel or whatever. I've tried a lot of different phrasing to try and search for something similar to no avail. It's 20"x14". I repaired the frame myself at the time I got it. My ex used to clear out houses for people so I don't know whether it was from NH or MA. No signature in either corner, but I doubt it's a famous artist. Either that roof is caving in or they were very amateur.

 

Possibly both - an amateur and the roof wasn't long for this world. Somebody cared about it though; they put it in a good frame.

 

It doesn't look like the work of a fully-trained artist. Can't see much in your photograph but... You've done a search for grist mills in those two states?

Debora