[Fred Nerks]

Erratic boulders...they sure get around, sitting on top of a mountain in the USA and on an island off the coast of Scotland...for example:

http://www.oceanlight.com/lightbox.php?x=glacial_erratic_boulder__mountain_and_peak__natural_world

http://www.tireeimages.com/collections41.html

...but the pic I really like is the one below with the huge 'pothole' - how might that have happened?

http://www.fotolibra.com/gallery/image/?s=4681826&sid=21

I agree. The builders of Stonehenge may have used erratics...it's the glacial origin that's not convincing IMO.

[blam]

"...but the pic I really like is the one below with the huge 'pothole' - how might that have happened? "

A water vortex when it was part of a stream in it's past?