The Preselis are the probable location of the quarry from where the bluestone was mined used in the second phase of the construction of an unusual stone circle in Wiltshire called Stonehenge. Seeing as how this is the only location in Britain the rock is found (a particular form of Blue Dolerite) one has to ask why did this rock had to be used, and if it was important then why that location (it is 135 miles away after all).
As an aside the bluestone was used for only part of stonehenge. The original site first existed as the earth bank and ditch enclosing a central area containing four stones at the solsticial points. Several hundred years later bluestones were brought and arranged in a circle within the henge. These stones are all about 3 meters tall (some part of which is below the ground) and have no lintels connecting the tops of the stones. That bluestone circle was dismantled and then partially re-erected as a different circle on the same site during the last phase of construction (over a thousand years after the site was first developed). This final phase in the building of stonehenge included the erection of the famous, characteristic and unique sarsen stone pillars topped with lintels.
Recent work on the carbon dating of material from various locations about the stonehenge site has come up with some detailed and interesting findings concerning the date and sequence of its construction. It now appears that the approximate dates we have for various parts of the monument are as follows:
Event in Stonehenge's History
8000 to 7000
Large wooden posts standing in deep holes, now located in the visitor's car park.
Date of the human bones found buried at the termination of the ditches surrounding the monument. These bones must have been preserved after the death of the person and kept for many years as they are much older than the date proposed for the construction of the ditches themselves.
Circular ditch and bank (henge) dug enclosing a central open space.
Circle of Sarsen stones erected. These are the large locally found stones which I had always imagined came last as they seem (along with the central, massive Sarsen trilithons) the most complicated part of the monument.
2450 to 2000
Avenue leading away from the circle towards midsummer sunrise constructed over this period. It is a wide avenue and not accurately enough placed, to be of much use for the prediction of the date of the solstice, but must have been built by people who already knew the direction in which to build it.
Initial stage of silting of the ditch, finds can be placed chronologically relative to each other by their position relative to this layer of silt.
The famous great trilithons were erected, the central horse shoe, comprising the most massive stones at the monument, also made from local Sarsen stone.
The bluestone circle was erected - these blocks are quite small at 3 metres tall each, but came from 200 km away in the Preseli hills of south Wales.
The central bluestone horse shoe erected.
Last discovered activity in the construction of the avenue (see 2450 BC).
Inner Z holes dug and filled with packing and cremations.
Outer Y holes dug and filled.
Pottery and a pin found deposited from this date.
Burial in the palisade ditch terminal. The site was obviously used well into the Iron Age, at this point the Celts would have been occupying the land. Though druids may have presided over the burial, they would have viewed the monument as a wonder, dating from before their known history. Despite the modern-day connection of druids and stone circles the two are separated by a lot of history.
For a while a prevalent theory was that the bluestones used in stonehenge were glacial erratics. That is bits of rock carried from some distance away by glaciers and dumped in a location where they would not normally be expected to occur. This theory has pretty much lost credible support as there appear to be no other similar erratics in the area - only those stones used in the circle itself.
A mate of mine proposed the most plausible explanation I have heard. He reckons the people whose circle it was, originally lived out in Pembrokeshire near the Preselis. They subsequently moved into the interior of the mainland, and took their most important belongings with them, including the circle. The move could have been prompted by climate or food source reasons. He may not be the first to propose this explanation but it was an original thought on his part.
It was either that or maybe it was only bluestones which were magically resonant in the right astral fields to adequately channel the orgone energy for the bronze age man's love temple.