Ah yes, as you say that just looks like some shading on the map.+Martin Helsdon
Indeed, I was of course just referring to the megaliths. Earthworks are all over the place and are, as you say, in a lot of cases either highly eroded or already destroyed. But there must be tons of undiscovered ones still out there. Aerial photography combined with the right soil conditions (e.g. after a drought) turns them up all the time, as I'm sure you know. Cursus features are quite fascinating to me, as are causewayed enclosures.