I was all ready to wade in with the old 'when is a recumbent stone circle not a recumbent stone circle' debate but noticed this had been dont to death before so in the interest recycling check out the old forum entries ; http://www.themodernantiquarian.com/forum/?thread=9844
No, I can't find that but it looks as though the rocks keeled over as they were halfburied in the soft earth of the henge. Most of the stones seem to be there ...