The National Geographic gets it more or less right...

I never thought I'd ever say this, but this appears to be quite a well-balanced report on the National Geographic web site....  and I like the bit about the sheep farm - makes it all sound very rural.  And "it's official" ?!!   What does that mean?  Has HM Office of Provenancing now given the official seal of approval?

Apart from the inevitable over-simplification here and there, we can live with this.

It's Official: Stonehenge Stones Were Moved 160 Miles

Ancient bluestones match outcrop near Wales sheep farm, experts say.

Dave Mosher

National Geographic Magazine 

http://news.nationalgeographic.com/news/2011/12/111222-stonehenge-bluestones-wales-match-glacier-ixer-ancient-science/

Published December 22, 2011

Some of the volcanic bluestones in the inner ring of Stonehenge officially match an outcrop in Wales that's 160 miles (257 kilometers) from the world-famous site, geologists announced this week.
The discovery leaves two big ideas standing about how the massive pieces of the monument arrived at Salisbury Plain: entirely by human hand, or partly by glacier.
As it looks today, 5,000-year-old Stonehenge has an outer ring of 20- to 30-ton sandstone blocks and an inner ring and horseshoe of 3- to 5-ton volcanic bluestone blocks.
The monument's larger outer blocks, called the Sarsen stones, were likely quarried some 20 to 30 miles (32 to 48 kilometers) away in what's now England, where sandstone is a common material.
The origin of the bluestones, however, has weighed heavy on the hearts of archaeologists. Rocks resembling the material under a microscope haven't been found anywhere relatively near Stonehenge—at least until now.

[[ That of course is untrue -- we have all known since 1922 that many of the stones have come from the eastern Preseli area.  It's the PRECISE provenancing that's new.....]]

Pinpointing the stones' origins is crucial to understanding how so many heavy hunks of rock made their way to the open plain where Stonehenge now stands.
"There's no way of explaining how these stones were transported without knowing where they came from," said study co-author Robert Ixer of the Univ of Leicester in the U.K.

Stonehenge Source Near Sheep Farm
For about two decades, Ixer and study co-author Richard Bevins, of the National Museum of Wales, have searched for the origins of the bluestones in outcrops around Wales.
As late as two years ago, the pair thought the blocks couldn't have come from the country—no samples from Welsh outcrops matched the Stonehenge blocks.
But not all of the samples collected over 20 years had yet been prepared for examination under a microscope. To be absolutely certain, the geologists began slicing up their remaining rocks.
The very first one—a chunk of rock collected in Wales 20 years ago—was a perfect match to the Stonehenge bluestones. The geologists spent the next two years checking a piece of Stonehenge bluestone against other outcrops around Wales.
"We sampled extensively and did not find anything that came anywhere close," Ixer said.
The rocky outcrop fingered by the duo's analysis is called Craig Rhos-y-Felin, which is now located on private land near a sheep farm.
The site is a long, bush-covered set of crags the size of four double-decker buses.

Next Step: Search for Tool Marks
The new find leaves two prominant theories for how the Welsh rocks got to Salisbury.
Humans could have quarried the site and dragged the blocks on wooden rafts. Or a giant glacier may have chiseled off the blocks and ferried them about a hundred miles (160 kilometers) toward Stonehenge, with humans dragging them the rest of the way.
If humans did the digging, archaeologists might detect marks left by tools or some other evidence. But if signs of human quarrying are lacking, the glacier idea might gain the upper hand.
"If we could find a quarry site," Ixer said, "we could tell if mankind was involved" in carving out the blocks.
But settling the issue, Ixer says, isn't up to geologists such as himself: "I have never betted in my life" and will not start now, he said.
"We need archaeologists. If they can show the rocks were quarried, that would suggest those rocks were transported by man."

[[We might add to that:  "We  also need geomorphologists.  If they can show that the rocks were quarried by overriding ice, that would suggest that those rocks were transported by a glacier."  It's interesting that the geologists hardly ever mention their earth science colleagues in this context, or admit that they have a real contribution to make.  What was I saying about "geology in the service of archaeology"....?]]