New research has cast doubt on the journey which the Stonehenge Bluestones - the famous stones formimg the distinctive inner circle and horseshoe of the ancient monument - took from Pembrokeshire to the famous site in present-day Wiltshire. One type of bluestone, the so-called spotted dolerite, was convincingly traced to the Mynydd Preseli area of North Pembrokeshire in the 1920s, but the origins of many of the others have remained a mystery. However, whilst the new findings have also linked a second type of stone - rhyolites - to the area, they call into question how the stones arrived in Wiltshire.
     Perceived wisdom had it that Stone Age man transported the giant slabs via raft, up the Bristol Channel and River Avon. But the recent findings point to a source for the stones in a major group of volcanics to Pont Season north of the Preseli Hills. So, it may look unlikely that ancient people would have been able to navigate the terrain in order to get the enormous rocks to the coast. An alternative theory was that nature drove the stone to Stonehenge, in the path of an Ice Age glacier, although the absence of any other Welsh rock in the region seemed to have ruled out the possibility.
     Dr Richard Bevins, Keeper of Geology at Amgueddfa Cymru, in partnership with Dr Rob Ixer, University of Leicester and Dr Nick Pearce of Aberystwyth University, have been working on the rhyolite component of the bluestones, which leads them to believe it is of Welsh origin. "If humans were responsible then an alternative route might need to be considered. However, if, as some believe, the stones were transported by the actions of glacier sheets during the last glaciation, the Pont Saeson discovery will need appraising in the context of this hypothesis. It's a further step towards revealing why these mysterious stones were so special to the people of the Neolithic," Dr Bevins said.
      A very detailed mineralogical analysis with Dr Nick Pearce from the University of Aberystwyth allowed the researchers to get some unexpected results. "The first result was the recognition that the huge sandstone Altar stone does not come from Milford Haven but from somewhere between West Wales and Herefordshire and has nothing to do with the Preseli Hills. This calls into question the proposed transport route for the Stonehenge bluestones. The second unexpected result was that much of the volcanic and sandstone Stonehenge debris does not match any standing stones - it may be the debris is all that is left of lost standing stones: it is difficult to see what else it could be. The third is that the geographical origins for many of the Stonehenge rocks are not from impressive outcrops high on the hilltops but in less obvious places, some deep in valleys," Dr Ixer said.
     But the new match does not explain the absence of any other Welsh Bluestone in the Stonehenge area, if indeed glaciation was responsible for carrying them there. Prof Mike Parker Pearson, from Sheffield University, called it "a hugely significant discovery which will fascinate everyone interested in Stonehenge. It's a further step towards revealing why these mysterious stones were so special to the people of the Neolithic."
     The team of researchers is now looking for the sources of the other Stonehenge volcanic and sandstone rocks.

Edited from BBC News, Culture24 (22 February 2011), University of Leicester (25 February 2011)