The Wiltshire Downs and Salisbury Plain is mostly chalk/limestone. That is a porous rock which will expand and contract on water ingress/egress and be affected by atmospheric humidity. I've no real idea but I suspect that Stonehenge will rise and fall vertically(ish) on a seasonal and other longer rhythms.
Widdershins: "in a direction contrary to the sun's course.." Interesting. The Eurasian plate is moving east, which is widdershins to the longitude, but not the latitude.
( Note: I am a Scot, and added widdershins to my dictionary. )
