It's worth mentioning that the Ordnance Survey didn't employ any archaeologists until the 1920s, and "stone" on a map in non-antiquity typeface means just that, a stone. It didn't have to be standing, or have anything to indicate artificial placement. It was just a stone big enough to warrant someone noticing it. I'm sure there were guidelines about how big a stone had to be to show, but I'm also fairly certain that different surveyors/draughtsmen interpreted the guidelines slightly flexibly!
None of which is to dismiss the idea that there could have been circles, just to point out that in itself a "stone" appearing on a 19th century 6 inch map is a pretty unreliable basis for a theory without something else to support it.
So I shall add this lost piece of information gleaned from the map to the Bitton Barrow http://www.themodernantiquarian.com/site/5494/bitton.html, though the stones seem to have no logic, history has laid them alongside a Roman road, which would seem to prove that earlier settlements existed. Thank you for making me go back and visit an old 'theory'....
http://maps.nls.uk/geo/explore/#zoom=16&lat=51.4175&lon=-2.4674&layers=6&b=1
