There are a lot of Sarsens that have been reused to control the flow of the Ogbourne at its source.
There is a strange conical mound that I have yet to find that Hamish Millers claims is a node on the Mary ley line in his book The Sun and the Serpent (p196) but locals I know claim it is a recent construction.
Looking at the photo in the book the top of the mound appears too pointed for it to old.