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Wednesday, 19 February 2014

Planet Earth -- still more interested in myth than reality?

 At the end of this piece I have posted  the new report on the NERC web site of the latest research by Bevins, Ixer and Pearce on the Carn Goedog rock identifications: 

"Carn Goedog is the likely major source of Stonehenge doleritic bluestones: evidence based on compatible element geochemistry and Principal Component Analysis"
Richard E. Bevins, Rob A. Ixer, Nick J.G. Pearce
http://www.sciencedirect.com/science/article/pii/S0305440313003956

ABSTRACT:  The Stonehenge bluestones were first sourced to outcrops in the high parts of the eastern Mynydd Preseli in SW Wales by H.H. Thomas in the early 1920s. He recognised the distinctive ‘spotted dolerite’ from his fieldwork in that area and suggested that the tors of Carn Meini (also known as Carn Menyn) and Cerrigmarchogion were the most likely sources. In the early 1990s, in a major contribution to our understanding of the Stonehenge bluestones, the geochemistry of a set of samples from Stonehenge monoliths and debitage was determined and compared against the geochemistry of dolerites from the eastern Mynydd Preseli by a team from the Open University led by R.S. Thorpe. They argued that the majority of the Stonehenge dolerites could be sourced from outcrops in the Carn Meini-Carn Gyfrwy area, based on the concentrations of the so-called ‘immobile’ elements (elements which are not affected by rock alteration processes), in particular TiO2, Y, and Zr. However, these elements are incompatible during crystallization of mineral phases in basaltic systems (that is they do not enter into the mineral phases which are crystallizing but are concentrated in the residual liquid) which severely hampers their use in discriminating between different pulses of an evolving magma (as is the case of the doleritic sills emplaced high in the crust and now exposed in the Mynydd Preseli). An alternative strategy in this study re-examines the data set of Thorpe's team but investigates the concentration of elements which are compatible in such basaltic systems (that is elements which do enter into the crystallizing mineral phases), namely MgO, Ni, Cr and Fe2O3. On the basis of the abundances of these elements on bivariate plots and also by using Principal Component Analysis on the dataset available and various sub-sets we identify three compositional groupings for the Stonehenge doleritic monolith and debitage samples and conclude that the majority of them (Group 1 of this paper) can be sourced to the prominent outcrop in the eastern Mynydd Preseli known as Carn Goedog. We also offer potential sources (with one exception) for those Stonehenge dolerites which appear not to relate to Carn Goedog.


We have looked at this paper before, so there is no need to analyse it again.  What's interesting is the article, published in a journal (web based) devoted to the Earth Sciences.  Look at the heading -- totally absurd, since presumably the author is an earth scientist herself.  Could she not bring herself to say " New evidence brings bluestone human transport theory into question" or something similar?  That shows us just how far the human transport myth has penetrated deep into the souls of people who should know better.......  even within the Earth Sciences research community.  How sad.

As for the article, it's pretty straightforward, and it's good to see that HH Thomas's science and his motivation are at last being questioned by professional geologists -- as I have done often before on this blog.  Just put "HH Thomas" into the search box to uncover some of my past comments.....

Assuming that Richard Bevins is being quoted correctly, he does seem to be getting much more critical and questioning of the archaeological orthodoxy.  At last!!

This is the key para:  "If Carn Goedog is the true origin of the dolerites, and Craig Rhos-y-felin is a source of the rhyolitic bluestones then it does bring into question the stones being transported by rafts down to the Bristol Channel, because both of these outcrops lie on the northern side of the Preseli Hills. The rocks would have had to be dragged up the hills, across the summits and back down again before they even reached the waterways. It's just not likely," Bevins concludes.

Welcome to the club. But if Richard was prepared to go this far, why could he not just have added:  "The locations of these possible source areas on the north -- or up-glacier - flank of Preseli is entirely in tune with glacial theory, and increases the likelihood that the stones are glacial erratics picked up by over-riding ice and transported at least part of the way towards Stonehenge."

Now if he had said that, and if it had been reported in this short article, we might have an indication of  earth scientists actually taking seriously the comments of their own colleagues, instead of going with the archaeological orthodoxy.  And if you think that indicates a degree of frustration on my part, you would be quite right.......

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Did humans transport Stonehenge rocks further than previously thought?

17 February 2014, by Harriet Jarlett
http://planetearth.nerc.ac.uk/news/story.aspx?id=1611&cookieConsent=A

Scientists have pinpointed the exact source of many of the rocks used to build Stonehenge.

A new study, published in the Journal of Archaeological Science, suggests that the site researchers had previously thought was the starting place of many of Stonehenge's rocks may not have been the source after all. Instead, it looks like the rocks actually come from a different site three kilometres away.

The findings, bring into question the long-standing theory that people transported the rocks from Wales to Wiltshire in order to build the monument.
The research focused on the smaller stones at Stonehenge, called bluestones. The chemistry of these rocks varies, but they all originate from the Preseli Hills in Wales and are thought to have been transported to the Stonehenge site over 4000 years ago.

By confirming the source of the rocks, the researchers hope to help answer the long standing question of how around 80 of these bluestones, weighing up to three tonnes each, were transported 250 kilometres from southwest Wales to Wiltshire.

'The Holy Grail question is how were the stones moved and why,' explains Dr Richard Bevins of National Museum of Wales who led the research. 'Many people think humans transported the stones south, down from the Preseli Hills and then up the Bristol Channel on rafts. But a second school of thought says these rocks are glacial erratics that were transported by ice to Salisbury Plain and so were available in the local environment.

'We're trying to discover the source of the stones so archaeologists can excavate sites in order to see if they can find evidence for people working the source stones,' he continues.
Scientists have known the bluestones originated from the Preseli Hills since 1923, when H. H. Thomas from NERC's British Geological Survey recognised the distinctive dark grey spotty rocks, known as spotted dolerites, during fieldwork. Further work in the early 1990s then tried to tie down the specific locations of the rocks' origin by matching the chemistry of the Stonehenge bluestones with those at the proposed origin site.

'The earlier research looked at the source of one of the spotted dolerites and tied it down to a specific outcrop, Carn Meini. It seems Thomas wanted all of the bluestones to also come from that same small area so he argued the rhyolites came from a nearby outcrop, Carn Alw. When we looked at it again we realised the descriptions of the rhyolites from Carn Alw and those at Stonehenge didn't look the same at all,' says Bevins.

The team took images showing the rocks at Stonehenge and the rocks at Carn Alw. They then asked members of the public with no geological background whether they looked the same.
'We asked people "does A look like B?" and everyone said no,' Bevins continues. 'This is astonishing because this has not been questioned since the original publication by Thomas in 1923.'

The team used a new method of identifying the chemical makeup of the rocks, to match the rocks with their origin. They believe that they have now identified Carn Goedog as the source of at least 55 per cent of the spotted dolerite bluestones at Stonehenge.

'If Carn Goedog is the true origin of the dolerites, and Craig Rhos-y-felin is a source of the rhyolitic bluestones then it does bring into question the stones being transported by rafts down to the Bristol Channel, because both of these outcrops lie on the northern side of the Preseli Hills. The rocks would have had to be dragged up the hills, across the summits and back down again before they even reached the waterways. It's just not likely,' Bevins concludes.

20 comments:

TonyH said...

The wheels of Bureaucracy and self interest [and that is essentially what we are dealing with here] move exceedingly slow..... BUT.....one of these days there'll be a new dawn, and a new day.......and I'll be feeling good!!!

TonyH said...

But I am very, VERY, pleased that Richard Bevins, whom, it could be argued, has been too long (psychologically at any rate), under the thrall of Mike Parker Pearson and his 'National Geographic - inspired bold and sturdy prehistoric adventurers' scenario, has now been brave enough to express his own opinion, and say that the plausibility of the Bristol Channel rafting scenario has been diminished by the latest geological evidence and analysis.


And Richard does say, also:-

"But a second School of Thought says these rocks are glacial erratics that were transported by ice to Salisbury Plain and so were available in the local environment".

Let us trust that Richard will give a decent amount of space in the National Museum of Wales to this 2nd school of thought, in his newest interpretation panels presenting the 'Blue Stone Enigma' to visitors. And that Pembrokeshire Coastal National Park will duly do the same....

chris johnson said...

I don't think Bevins is sticking his neck out to debunk the rafts - although I seem to recall that there is a TV program in the make proving the possibility of sea transport from Cardigan. Whatever ever happened to that one?

Actually, should one believe in human transport, a lift over the Presceli ridge is relatively simple compared to what had to follow.

Shame Richard does not clarify his position here. We are generally friendly. And whatever happened to Myris??

TonyH said...

I reckon Richard Bevins' piece does herald a watershed, so to speak, perhaps imperceptible to some, but a watershed nevertheless in this entire debate, and I think Brian discerns this too.

Megaliths have never been shown to have been trundled anything even approaching this far anywhere in prehistoric Europe- this has been well trumpeted by the MPP messenengers. And, also, whatever happened to GeoCur?

TonyH said...

I'm sure many of us on this Blog wish Earth Scientists like Rob Ixer and Richard Bevins all the best in expressing their own independently-arrived-at opinions as to what mode of transportation those orthostats (and the so-called debitage) took on their journeys from Preseli to Salisbury Plain, or relatively close by.

BRIAN JOHN said...

Thanks for the comments, folks. I can't really add very much -- I simply have to assume that Richard's views are accurately represented, and that if they are not, he will put in an appearance on this blog and say so!!

Phil Morgan said...

Hello Chris,
The documentary covering the sailing of a bluestone around the coast was made for an American audience.
I was informed that the operation was a success.

Hello Tony,
There was about 270 cubic kilometers of Blue Pennant Sandstone removed from the south Wales plateau by the Welsh Ice Cap, i.e. the same ice that joined the Irish Sea Ice which it is suggested carried the bluestones.

That's enough rock to build a wall from Preseli to Stonehenge, but the wall would be a kilometre high by a kilometre wide.

Dr. Bevins is aware of the complete lack of Blue Pennant Sandstone erratics on Salisbury Plain. Could this be the reason why he's not wholly supporting the glacial transport theory?

Phil Morgan

BRIAN JOHN said...

Phil -- where on earth did you get that figure from?

Phil Morgan said...

Hello Brian,
I appreciate that you read geography at Oxford which makes me feel as though I'm teaching my granny to suck eggs, but nevertheless, it's a straight-forward calculation.

I used the Ordnance Survey Explorer Map number 166, and selected the glaciated Aberdare Valley, length 17.7 kms, as a target.
Cross-sections of the valley were taken at kilometre intervals which gave an average cross-sectional area of 0.62 square kilometres.

Multiplying the length of the valley by the average cross-sectional area gave the volume of the valley, which is 10.974 cubic kilometres.

Using the 'Wheresthepath' website allowed the lengths of all the valleys in the Blue Pennant Sandstone of the South Wales Coalfield to be estimated to a reasonable accuracy. This came to 447.37 kms.

Therefore for a 17.7 km advance, the glacier removed 10.974 cubic kilometres of rock.

For a 1 km advance the glacier would remove 10.974 divided by 17.7 = 0.62 cubic kms of rock.

Therefore, the total volume of rock removed from all the valleys in the the B.P.Sandstone would be 447.37 kms X 0.62 cubic kilometres, which equals 277.3694 cubic kilometres.

Say 270 cubic kilometres of rock removed by the Welsh Ice Cap.

To allow for erossion by wind, rain, and freeze-thaw since the last glaciation, no account was taken of the Cwm Clydach or Senghennydd valleys, or the many smaller tributary valleys that form to either side of the main valleys in the Coalfield.

I find it interesting that in your post of the 19th July 2013 on the Nordvest Fjord, East Greenland, you said:

"So the full depth of the fjord over a distance of about 80 miles is approx 3,300 m or 11,000 feet. I'll let somebody else work out how much material has been eroded and removed by ice from a trough this size..."

It takes a little time and effort, that's all.

Phil M

BRIAN JOHN said...

There are very big differences in the mid-latitudes, Phil, because glaciation here has been intermittent with each glacial episode relatively short-lived. Non-glacial processes have been far more important in valley formation than glacial processes, in the Brecon Beacons and coalfield valleys. In contrast, in the high Arctic, glacial processes have been more or less continuous, over many millions of years.

Phil M. said...

Hello Brian,
I'm not being arguementative over this, but I wasn't comparing the glaciation of mid-latitudes, to that of the high Arctic. I was simply showing that the calculation is the same for both areas.

However, when compared to the high Arctic, the latitudes of the Preseli Hills and the South Wales Coalfiled can be classed as near identical.

The following extract shows agreement with your thoughts on mid-latitude erosion:
The 'Geology Of The South Wales Coalfield, Pt IV, Pontypridd and Maesteg, HMSO 1964', states that "It appears likely, however, that the district underwent at least one complete cycle of subaerial erosion", and, "during the Pleistocene the district was invaded by glaciers which produced minor modifications of the landscape; since the melting of the ice, few changes of significance have taken place."

To my mind it would seem that because the Preseli Hills form a dome-like structure, it is difficult to establish the amount of rock that has been removed. If this amount was minimal, then it may account for the fact that no bluestone erratics exist east of the Bristol Channel.

Nevertheless, because the massive Blue Pennant Sandstone formations form a clear, deeply incised, plateau, the amount of rock removed can be estimated with reasonable accuracy.
What is unknown, however, is how much of that rock was removed by glacial action. If 75% of the volume extracted from the coalfield valleys was attributable to subaerial erosion, then that still leaves 67 cubic kilometres of rock removed by the Welsh Ice cap; of which zero reached Salisbury Plain.

Doesn't this imply that the combined glaciers of the Irish Sea Ice, and the Welsh Ice Cap, failed to penetrate into present day England?

Phil M.

BRIAN JOHN said...

Phil -- if only the processes at work in the natural world were so simple! One obvious point -- absence of evidence is not evidence of absence. Neither you nor I knows whether there ever were -- or still are -- bits of Blue Pennant Sandstone on Salisbury plain.

I wish I knew where all the rock from the excavation of Nordvestfjord has ended up?

Your assumption about the Irish Sea Glaciuer not penetrating into SW England is contradicted by the evidence. There are glacial deposits from the Irish Sea Glacier in the Bristol-Bath area, as I have repeatedly pointed out on this blog.

Phil M. said...

Hello Brian,
"Neither you nor I knows whether there ever were -- or still are --bits of Blue Pennant Sandstone on Salisbury plain."

Very true, and the same can be said for Bluestones, and so the circle continues.

TonyH said...

Phil

Like Brian, I trained as a Geographer. Unlike Brian, I'm far more the "jack-of-all-trades" variety of Geographer, whilst he is both that, and a Glacial Geographer at Doctorate level. However, for what it's worth, I'm keen on local history and there is some Sandstone rock very much in evidence in the village street "furniture" of the village of Rode, on the Wiltshire/Somerset border, a few miles north of Frome, and no distance from Salisbury Plain and Westbury.

One lump of this non-reshaped sandstone is on the ancient packhorse bridge over the river Frome (which river was confidently stated by Richard Atkinson as being the route our so impressive prehistoric forefathers took, by coracles or similar(?) in transporting various assorted 'bluestones' from you-know-where to you-know-where-else.
There may well also have been a Neolithic or Bronze Age barrow very close to the packhorse bridge [place name evidence:- "Barrow Farm" 200 metres away] and equally close to the other piece of sandstone within the village nucleus. But I don't know whether it's Pennant.

TonyH said...

Those Rode stones can't be Pennant Sandstone, as they're reddy-pink. Perhaps they are a sandstone relatively local to the Frome area, Brian?

BRIAN JOHN said...

I wish I knew the local sandstones better. As it is, I couldn't possibly comment......

TonyH said...

Have just been looking back at one of the earlier Posts, "The Stonehenge Sandstone Mystery (1)", 16 April 2012. Many fascinating/ witty comments in the Postbag on all matters Sandstone and Bristol Channel/ South Wales/ Bath & Bristol Glaciation/ How To Discern A Glaciated Landscape, etc. Worth a look back!

Phil M. said...

Hello Tony,
Thanks for the information,when the British Geological Survey, 'Geology of Britain Viewer' is working again I'll have a look at the bedrock in the Frome area.
Phil

TonyH said...

Thanks, Phil.

The search for erratics and for more subtle signs of glacial activity in the general vicinity of Frome/ Bradford-on-Avon as well as further east must continue.

There is a Wiltshire GEOLOGY Group based, it seems, at the Wiltshire Heritage Museum, Long Street, Devizes. Its email address is:-

info@wiltsgeology.org.uk

I expect Isobel Geddes, whom Brian is aware of and who has commented on this Blog occasionally, is involved in the Group.

Phil M said...

Hello Tony,
The British Gelogical Survey's Geology of Britain Viewer is working again.
in case you're unfamiliar with it there are five Steps to Google:

1). British Geological Survey;

2). Discovering Geology;

3). Geology of Britain;

4). Geology of Britain Viewer is highlighted in blue;

5). Open Geology of britain viewer.

A very useful site.

BW,

Phil