This might make you laugh. I call it 'The case of the curious curve.'
While I was looking at the southern inner circle at Avebury, trying to decide for myself if there were 29 or 30 stones originally, I looked at the historical maps on Google for 2003 and seemed to see a definite curve marked out on the ground:
I looked also at the Google map for 2002 and sure enough, there it was again:
Now this line is in a clear open field and there is no reason for any modern person to walk this exact line to the extent that it makes itself visible from a satellite picture, several years running.
I concluded that the track was ancient, probably dating from a time when there were more stones in the circle. At the north-east, the track seems to curve in more. I assumed that this was because the existing stones gave out at this point and people made a bee-line for the corner of the garden and exited that way. I thought the curve in the grass might be because of a change in vegetation. Perhaps the stones were fenced off, so the undergrowth grew outside the circle of stones and people walked around that and we can still see it, just like we can still see the ancient pasture boundaries in these pictures.
Now my putative circle of 30 stones, rather than a smaller circle of 29 stones, seemed to fit this crop feature better. I know the next diagram below is confusing, but the red lines and orange numbered stones are the conventional 29 stone solution published everywhere, whereas the white hatched lines and white circles are where I think a 30 stone circle really went. There are only those five stones left today in the south west:
The curious curve followed my white line very well until the stone marked 125 where it tracks in.
I looked at Aubrey's old plan, pre-Stukeley, the earliest plan we have:
Yup, he shows existing stones petering out exactly where I was thinking the stones petered out and the cropmark started to veer away from a nice circle.
So surely I am on the right track? No, of course not.
So what is the answer? What made that track so prominent that it shows on Google from year to year?
It was Pete Glastonbury to the rescue. "Ah, that will be Gordon", he says.
"Gordon who?", I say.
"Gordon Rhymes", says Pete.
"OK", I thought.
Pete then told me he'd showed Gordon where the missing stone depressions in the soil are, which are visible on the ground. I've looked too, you can actually see them better on the ground than in aerial photos.
Each and every day, being a pagan fluid Druid dude, Gordon dutifully walked this exact path for some years, causing the rut visible on Google. Gordon is still to be seen playing guitar in the Red Lion at Avebury on some nights, but regrettably he has ill health and no longer is able to walk the path every day.
You can enjoy Gordon walking his path here on Youtube:http://yt.cl.nr/lQOa9SWKNsg
Now the interesting thing for me is it is a proof of some kind for my construct. Because Gordon was walking outside the visible depressions (clockwise, by the way, as all good Druids do, sunwise) he was in fact establishing for me where the stones went, which is a bigger circle than conventional estimates. So I believe Stukeley was right in saying 30 stones for this circle, not the 29 you will see on most reconstructions.
Gordon's circle and my circle of 30: