Prof Tim Darvill, who's heading the current Stonehenge excavations, found what he reckons is the quarry where the bluestones came from at Carn Menyn in the Presellis.

The big problem with the glaciation theory is there's no 'trail' of bluestone debris between Wiltshire and Wales. It seems ridiculous to assume that either

a) every piece of bluestone was collected

or

b) There wasn't much anyway and the glacier conveniently left what there was on Salisbury Plain