Stonehenge 181
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Stonehenge

Stone shifting 5

I agree with all your points and I think the idea was generally dismissed for those reasons.

However, it would aid getting the stone across marshy ground using Gordon's method .....

Do we know what the climate was like in those days? The winter of 1987 was sufficiently severe to freeze the top 10" of ground (I know 'cos I was digging foundations for my house), so that would have been more than ample to render boggy ground passable. However, in recent years, the ice crust would have been pretty thin. I don't think it would have supported a 40 tonner.