Experts have argued that the large sarsen stones at Stonehenge are local to the Salisbury Plain area. However, the origin of the smaller bluestones has been the topic of research for many years, although there has been little refinement of the research conducted by geologist Herbert Henry Thomas in 1923 about their original sources.
The new paper by Dr Richard Bevins (Amgueddfa Cymru – National Museum Wales), Dr Rob Ixer (Institute of Archaeology, UCL) and Professor Nick Pearce (Aberystwyth University), will soon be published in the Journal of Archaeological Science.
Spotted dolerite location In 2011, Bevins and Ixer confirmed for the first time the exact location of some of the bluestones known as rhyolites (a type of silica-rich igneous rock). Their research identified the source of the stone to the prominent outcrop of Craig Rhos y Felin near Crymych, Pembrokeshire. Now – along with Pearce – they are confident of the location of another major type of bluestone – the spotted dolerite (a type of relatively silica-poor igneous rock containing distinctive alteration spots).
H.H. Thomas from the Geological Survey published a paper in The Antiquaries Journal in which he claimed to have sourced the spotted dolerite component of the Bluestones to hilltop rock outcrops, exposed in the high Preseli, to the west of Crymych in west Wales. Specifically, he thought that the tors on Carn Meini and Cerrig Marchogion were the likely source outcrops. He went on to speculate about how humans had transported the stones to the Salisbury Plain, favouring transport across land rather than a combined land and sea journey. As a result of Thomas’s views recent archaeological excavations have concentrated on finding Stonehenge-related quarries at Carn Meini.
Using geochemical techniques, Bevins, Ixer and Pearce have compared samples of rock and debris from Stonehenge with Thomas’s findings and also geochemical data published in the early 1990’s by Richard Thorpe and his team from the Open University. The current findings conclude that the majority of the spotted dolerites analysed actually come from Carn Goedog which is about 1.5km away from Thomas’s originally proposed site of Carn Meini.
Dr Richard Bevins (Amgueddfa Cymru) who has been studying the geology of Pembrokeshire for over 30 years said:
“When the first part of our research was announced in 2011, we communicated our commitment to continue to work in the area and we have added to that initial work with papers in 2012 and 2013. I am very pleased that we have continued to revisit the area and be able to further study the standing stones and debris from Stonehenge!
“The geology of Pembrokeshire is unique, which is why I have spent so much time in the area. The area has much to offer in helping us understand what happens when magma is erupted from underwater volcanoes, and how those igneous rocks are transformed by the effects of increased temperatures and pressures during later mountain building events. Equally interesting of course is the fact that these igneous rocks have been used in the construction of Stonehenge and only once we know their correct geographical origins can we fully interpret the archaeological significance.
“I hope that our recent scientific findings will influence the continually debated question of how the bluestones were transported to Salisbury Plain.”
Continue the research
Dr Rob Ixer who studied his first Stonehenge bluestone twenty-five years ago said:
“As this and earlier papers show, almost everything we believed ten years ago about the bluestones have been shown to be partially or completely incorrect. We are still in the stages of redress and shall continue to research the bluestones for answers. This paper is a very important component of this search and must re-direct us (and others) to relook at the standing stones, their debris and possible quarry sites so that we can correctly determine their origins.”
Past Horizons. 2014. “Major source of Stonehenge spotted dolerites located”. Past Horizons. Posted: November 20, 2013. Available online: http://www.pasthorizonspr.com/index.php/archives/11/2013/major-source-stonehenge-spotted-dolerites-located