Is there any clear evidence of glacial flow from the Preseli area to the Stonehenge area, or at least to the Avebury area, where the sarsens came from?

In other words, were the bluestones selected, like the sarsens, because the lay within a reasonable area to be drawn from? Why were the bluestones all deposited in one small area, with no other examples to be found today?

If not, then it's hard to believe any other theory than the Preseli one. There are prehistoric bluestone quarries there, and semi-dressed stones have been found there of the same shape and size as those found at Stonehenge. If a bluestone circle existed in the Preseli area, then it could have been robbed and taken to Stonehenge, but it would still mean the architects took it all that way.

Cheers,
TE.