It is, isn't it? I've not seen that before. Scuze my ignorance, but is there any significance to the segment of a large "circular" feature in the top right hand corner (just above where the cursus ends)? I had a quick glance at a map of the environs here:

http://www.archaemedia.net/st1.asp

and as far as I can see the segment isn't in the right position for Durrington Walls.