Some interesting posts on this. Pont Saeson is in the area of Fishguard Volcanics, running in a broad swathe of country from the eastern end of Preseli along the North Pembs coast and towards Strumble Head. Have a look at my Stonehenge Thoughts blog and do a search for "Pont Saeson". I've considered the new evidence at length.

No reason to get all excited about the discovery that one or more of the Stonehenge bluestones came from Pont Saeson or somewhere near it. After all, there are more than 30 different stone types represented at Stonehenge -- and every new piece of geology seems to suggest additional stone sources. As Judd suggested a very long time ago, this simply looks like a collection of glacial erratics. Pont Saeson, Carn Goedog, Carn Alw, Carn Llwyn, Carn Clust-y-ci and other sites on the northern slopes of Preseli are exactly the sort of places where you would expect glacial entrainment to occur, with ice coming in from the NW and flowing towards the SE. I think more locations will be found in that general area as the geology work by Rob Ixer and others proceeds.

In my view the key factor in the decision to build Stonehenge where it is was simply the availability of stones -- of many types and sizes. That in itself may have given the area "significance" or "power" and triggered off the building project. The stones will not ALL have been AT Stonehenge -- they may have been scattered over quite a wide area. To assemble them and use them was undoubtedly an impressive feat. Why destroy a good story by bringing in all this fanciful stuff about mighty land and sea journeys by intrepid stone collectors? It was fanciful in 1922, and it is infinitely more fanciful today, now that we know much more about geology, glaciology and geomorphology.