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It is an archaeological enigma which last week a team of experts professed to have resolved: if and how the ‘bluestones’ at Stonehenge were excavated and transported from Pembrokeshire by our prehistoric ancestors.

The team of archaeologists and geologists – led academics from University College, London, said they definitively confirmed two sites in the Preseli Hills – Carn Goedog and Craig Rhos-y-felin - had been quarried for two types of stone.

It was suggested the stones were first used in a local monument, somewhere near the quarries, that was then dismantled and dragged off to Wiltshire.

Read more: Source of Stonehenge's 'bluestones' discovered... and they ARE definitely from Wales

But the assertions on how the stones were removed and transported, apparently leaving evidence so-called “engineering features,” have been branded “all wrong” by another team of earth scientists, in a conflicting report published today.

(Image: Adam Stanford © Aerial-Cam Ltd.)

In a peer-reviewed paper published in the Archaeology in Wales journal, Dr Brian John, Dr Dyfed Elis-Gruffydd and John Downes say there are “no traces of human intervention in any of the features that have made the archaeologists so excited”.

The group does not accept the idea of a Neolithic quarry in the Preseli Hills and says the supposed signs of ‘quarrying’ by humans at Craig Rhos-y-Felin were entirely natural.

They also believe that the archaeologists behind the report may have inadvertently created certain features during five years of “highly selective sediment removal”.

“This site has been described by lead archaeologist Prof Mike Parker Pearson as ‘the Pompeii of prehistoric stone quarries’ and has caused great excitement in archaeological circles,” says the report.

“The selection of this rocky crag near the village of Brynberian for excavation in 2011-2015 was triggered by the discovery by geologists Richard Bevins and Rob Ixer that some of the stone fragments in the soil at Stonehenge were quite precisely matched to an unusual type of foliated rhyolite found in the crag.

“This led the archaeologists to conclude that there must have been a Neolithic quarry here, worked for the specific purpose of cutting out monoliths for the bluestone settings at Stonehenge.”

But Dr John is increasingly convinced that the rhyolite debris at Stonehenge comes from glacial erratics which were eroded from the Rhosyfelin rocky crag almost half a million years ago by the overriding Irish Sea Glacier and then transported eastwards by ice towards Salisbury Plain.

In his paper written with Dr Dyfed Elis-Gruffydd and John Downes, he says: “It is suggested, on the basis of careful examinations of this site, that certain of the “man made features” described have been created by the archaeologists themselves through a process of selective sediment and clast removal.

“An expectation or conviction that ‘engineering features’ would be found has perhaps led to the unconscious fashioning of archaeological artifices.

“While there appears to be no landform, rock mechanics or sedimentary evidence that this was a Neolithic quarry site devoted to the extraction of bluestone orthostats destined for use at Stonehenge, or for any other purpose, we would accept the possibility that there may have been temporary Mesolithic, Neolithic or later camp sites here over a very long period of time, as in many other sheltered and wooded locations in north Pembrokeshire.”

(Image: Adam Stanford © Aerial-Cam Ltd.)

Commenting on the research paper published last week, Dr Brian John added: “The new geological work at Rhosyfelin and Stonehenge is an interesting piece of ‘rock provenencing’ – but it tells us nothing at all about how monoliths or smaller rock fragments from West Wales found their way to Stonehenge.

“We are sure that the archaeologists have convinced themselves that the glacial transport of erratics was impossible. We are not sure where they got that idea from.

“On the contrary, there is substantial evidence in favour of glacial transport and zero evidence in support of the human transport theory. We accept that there might have been a camp site at Rhosyfelin, used intermittently by hunters over several millennia. But there is no quarry.

“We think the archaeologists have been so keen on telling a good story here that they have ignored or misinterpreted the evidence in front of them.

“That’s very careless. They now need to undertake a complete reassessment of the material they have collected.”

Further excavations of the quarries are planned for 2016.