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Research chips away at Stonehenge mystery

According to the University of College London (UCL), which led the research team, geologists have known since the 1920s that the smaller stones in the Stonehenge structure, known as bluestones, originated in the Preseli Hills, a mountain range in west Wales, UK.

However, the archaeology team only recently began collaborating with geologists to locate and excavate the actual quarries from which the bluestones were sourced.

The combined research team included archaeologists and geologists from UCL, the University of Manchester, Bournemouth University, the University of Southampton, the University of Leicester, National Museum Wales and the Dyfed Archaeological Trust.

Quarry techniques

Stonehenge’s bluestones are composed of two types of volcanic and igneous rock, and the team identified the “Carn Goedog” and “Craig Rhos-y-felin” outcrops as the main sources for the spotted dolerite and rhyolite bluestones, respectively.

Dr Josh Pollard from the University of Southampton explained that the special geology of these outcrops formed natural pillars of rock, which would have allowed prehistoric quarry workers to detach large pieces of stone with relative ease.

“They only had to insert wooden wedges into the cracks between the pillars and then let the Welsh rain do the rest by swelling the wood to ease each pillar off the rock face,” he said. “The quarry workers then lowered the thin pillars onto platforms of earth and stone – a sort of ‘loading bay’ from where the huge stones could be dragged away along trackways leading out of each quarry.”

Transport routes

{{image2-a:r-w:320}}These new findings, and the location of the quarries on the north side of the Preseli Hills, challenge previous theories that suggested the bluestones were transported southwards and then floated on boats or rafts to their final resting place on England’s Salisbury Plain.

“The only logical direction for the bluestones to go was to the north then either by sea around St David’s Head or eastwards overland through the valleys along the route that is now the A40 [a major UK road],” the director of the research project, Professor Mike Parker Pearson of UCL’s Institute of Archaeology, commented.

“Personally, I think that the overland route is more likely. Each of the 80 monoliths weighed less than two tonnes, so teams of people or oxen could have managed this. We know from examples in India and elsewhere in Asia that single stones this size can even be carried on wooden lattices by groups of 60 – they didn’t even have to drag them if they didn’t want to.”

Timing questions

Radiocarbon dating of material retrieved from the prehistoric quarry workers’ camp fires also raised interesting questions about the timing of Stonehenge’s construction.

“We have dates of around 3400 BC for Craig Rhos-y-felin and 3200 BC for Carn Goedog, which is intriguing because the bluestones didn’t get put up at Stonehenge until around 2900 BC,” Pearson said.

“It could have taken those Neolithic stone-draggers nearly 500 years to get them to Stonehenge, but that’s pretty improbable in my view. It’s more likely that the stones were first used in a local monument, somewhere near the quarries, that was then dismantled and dragged off to Wiltshire.

“If we can find the original monument in Wales from which it was built, we will finally be able to solve the mystery of why Stonehenge was built and why some of its stones were brought so far,” Pearson added.

It was said that further excavation at the bluestone quarries was planned for 2016. Research is also being undertaken in north Wiltshire to trace the source of Stonehenge’s larger standing stones, which are composed of a sandstone local to the region called sarsen.

Research criticism

The team’s findings were recently published in the Antiquity journal, but not everyone is convinced of their validity.

Brian John, a geologist that is local to the Pembrokeshire area where the supposed Stonehenge quarries are located, posted a scathing critique of the UCL-led team’s research on his blog. He argued that the article omitted important scientific detail and had “a powerful bias”.

John has also previously been mentioned in the media for debunking the “bluestone myth” that quarry workers travelled hundreds of miles to drag the Stonehenge stones from the Preseli Hills to Salisbury Plain.

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Ancient route discovered at Stonehenge
Stonehenge's quarry discovered

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