Does this look like anything interesting, to those that know about such things?
http://www.geograph.org.uk/photo/430565
The RCAHMS record doesn't want to pick a date. There's various stories about it being somewhere to weigh wool. but then 'thirl' seems to have something to do with milling grain. It's on the boundary (where it changes direction). Just strikes me as a lot of effort to go to.