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Wednesday 27 September 2023

When is a bluestone not a bluestone?

From article (1).  Twenty-two groups of non-dolerite Stonehenge igneous debitage (or is it seven? or maybe eight?  or maybe thirty or more?)

Two new papers have kindly been brought to my notice -- each written by Bevins and Ixer together with assorted geological colleagues.  They don't currently seem to be behind paywalls, but I have copies which I can supply as Email attachments on request.

Here are the details:

(1)  Treasures in the Attic: Testing Cunnington’s assertion that Stone 32c is the ‘type’ sample for Andesite Group A
by Rob A. Ixer, Richard E. Bevins, Duncan Pirrie and Matthew Power.
Wilts Archaeol & Nat Hist Magazine, vol. 116 (2023), pp. 1–15


In 1881 William Cunnington excavated and sampled buried Stone 32c from within the Stonehenge Circle and described it as a ‘calcareous chloritic tuff’. He suggested that it was the source (type material) for similar looking debitage within the Stonehenge Landscape. Last described fifty years ago his original thin sections have been rediscovered and their investigation has shown that it was a reasonable conclusion based on his limited sampling. However, twenty first century investigations of thousands of pieces of this debitage, now defined as Andesite Group A (formerly Volcanic Group A), show it to possibly comprise two sub-groups, one being calcite-rich and the other being calcite-poor. Thin sections from Stone 32c show many of the characteristics of the calcite-bearing sub-group, but fewer of the calcite-poor sub-group but, for the present, Stone 32c is assigned as the type material for all Andesite Group A. However, Stone 32c may be the sole parent to all Andesite Group A debitage or only its calcite-bearing sub-group or it may share parentage for some or all of Andesite Group A with at least four other, as yet unsampled, stones (33e, 33f, 40c and 41d) buried within the Stonehenge Circle. Further research will answer these questions.


(2)  The Stonehenge Altar Stone was probably not sourced from the Old Red Sandstone of the Anglo-Welsh Basin: Time to broaden our geographic and stratigraphic horizons?

by Richard E. Bevins, Nick J.G. Pearce, Rob A. Ixer,  Duncan Pirrie, Sergio Ando, Stephen Hillier, Peter Turner, Matthew Power. 
Journal of Archaeological Science: Reports 51 (2023) 104215

Stone 80, the recumbent Altar Stone, is the largest of the Stonehenge foreign “bluestones”, mainly igneous rocks forming the inner Stonehenge circle. The Altar Stone’s anomalous lithology, a sandstone of continental origin, led to the previous suggestion of a provenance from the Old Red Sandstone (ORS) of west Wales, close to where the majority of the bluestones have been sourced (viz. the Mynydd Preseli area in west Wales) some 225 km west of Stonehenge. Building upon earlier investigations we have examined new samples from the Old Red Sandstone (ORS) within the Anglo-Welsh Basin (covering south Wales, the Welsh Borderland, the West Midlands and Somerset) using traditional optical petrography but additionally portable XRF, automated SEM-EDS and Raman Spectroscopic techniques. One of the key characteristics of the Altar Stone is its unusually high Ba content (all except one of 106 analyses have Ba > 1025 ppm), reflecting high modal baryte. Of the 58 ORS samples analysed to date from the Anglo-Welsh Basin, only four show analyses where Ba exceeds 1000 ppm, similar to the lower range of the Altar Stone composition. However, because of their contrasting mineralogies, combined with data collected from new automated SEM-EDS and Raman Spectroscopic analyses these four samples must be dis- counted as being from the source of the Altar Stone. It now seems ever more likely that the Altar Stone was not derived from the ORS of the Anglo-Welsh Basin, and therefore it is time to broaden our horizons, both geographically and stratigraphically into northern Britain and also to consider continental sandstones of a younger age. There is no doubt that considering the Altar Stone as a ‘bluestone’ has influenced thinking regarding the long-held view to a source in Wales. We therefore propose that the Altar Stone should be ‘de- classified’ as a bluestone, breaking a link to the essentially Mynydd Preseli-derived bluestones.


The first of these papers is yet another in the "dusty box" category, in which the geologists have discovered yet more "lost" or "forgotten" thin sections or rock samples which they now assign to one or another of their rock categories, which keep on being redefined at such a pace that those of us who try to keep up have long since given up in despair........  It's an exercise which no doubt keeps them amused, but one wonders how much use it actually is to anybody else. (Ixer, Bevins and co are not unique in this regard -- in glacial geomorphology there are also individuals and teams who delight in endlessly re-defining lithostratigraphic units, moving some upwards, others downwards, and others sideways, to the utter confusion of other specialists who prefer to get out and do some fieldwork.......)

The article contains some perfectly respectable analytical work, but reminds us that the bluestone assemblage at Stonehenge is so varied that classification schemes are essentially useless in our attempts to find out what happened on the site.  Over and again Ixer, Bevins and their colleagues have re-defined their major categories (for example Volcanic Group A which is now called Andesite Group A) and have had to admit that while some of their samples fall neatly within it, and maybe come from a single source area, others do not.   One of their diagrams seems to show 22 different rock types in the non-dolerite igneous groups, but they cannot tell us whether these have come from 22 different locations (or a smaller number) in the West Wales landscape.  There is nothing in this paper that contradicts my assertion that there are at least 46 different rock types in the bluestone assemblage, and that the sheer variety of lithologies and origins mitigates against bluestone quarrying, conscious stone collection and human stone haulage.

The conclusion of the paper is that "Andesite Group A comprises calcite-rich (including Stone 32c and possibly Stone 40c) and calcite–poor sub-groups. It may be that the calcite- poor sub-group should be reclassified into a separate lithic group(s) Andesite Group B, C etc that exclude Stone 32c (and possibly Stone 40c) as parents."  That's not going to make a headline in the Daily Mail or the Sun newspapers.........
When is a group not a group but a sub-group?  Ah, that is the question.......

This brings me to the fundamental defect in this paper.  Everything is based on the unproven assertion that all of the fragments of andesite bluestone (and all of the other bluestone fragments in the Stonehenge landscape) have come from existing monoliths, stumps or standing stones that have been destroyed.  These are referred to as "the parents".  That is illogical and unscientific.  This paper, which completely ignores the possibility that many of the fragments in the landscape have come from destroyed glacial deposits or from weathered erratics that have nothing whatsoever with Stonehenge, is therefore biased and unreliable, and I am amazed that the Editor of WANHM accepted it for publication in its present form.  Every study done by the geologists seems to throw up rock types that are NOT represented in the monolith assemblage, and the geologists are so obsessed with their ruling hypothesis that they seem to spend much of their time in a haze of classification and re-classification, much to their own confusion.

In refusing to accept that a proportion of the thousands of flakes, fragments, pebbles and cobbles in the Stonehenge landscape might have been there before human beings arrived on the scene, the authors of this article simply demonstrate, yet again, that they are obsessed with the confirmation, at all costs, of their ruling hypothesis of monolith quarrying and stone haulage.


The second paper is similarly obsessed with the human transport hypothesis, and the authors do not even have the good grace to mention the "glacial transport alternative."  Its publication has been accompanied by a press release and PR campaign typified by this wondrous effort from the Daily Mail:

"Stonehenge's Altar Stone did NOT come from Wales: Scientists debunk popular theory and claim the Neolithic slab may have been brought in from Orkney - over 682 miles away."

There is some mystery about what is going on at the moment, because Mike Pitts reported on this paper on Twitter (now called X) and then reported that it had been withdrawn because it contained errors.  All will no doubt be revealed in time.........

Anyway, for what it's worth this is possibly the most bizarre paper ever published by the Bevins / Ixer team, mixing science and speculation in a manner that out-does all their previous efforts.  As indicated in the abstract, they key assumption is that the bluestones have been "sourced" in the Mynydd Preseli area -- ie quarried or deliberately selected, picked up and carried off to Stonehenge.  Human transport of bluestone monoliths is simply assumed to have occurred, without any proper analysis of alternative explanations including the glacial transport theory.  This is unscientific, and it is even more unscientific to ignore the vast numbers of smaller bluestone (ie foreign) clasts in the Stonehenge landscape simply because they are inconvenient.  As mentioned above, every attempt to tie down  bluestone erratics to specific geographical source locations or lithological groups seems to lead to an admission that there are yet more samples that "do not fit".

So to the geological investigations. At the outset we see speculative statements dressed up as facts.  Craig Rhosyfelin has NOT definitively been identified as "the source of the main rhyolitic debitage at Stonehenge", and neither has Carn Goedog been identified as "the main source of the spotted dolerites."  These sources are possibilities at best, and the authors simply do not know enough about related rock outcrops and lithologies to allow them to claim definitive provenancing.  Quote:  "........the bluestones in fact represent one of the longest transport distances known from source to monument construction site anywhere in the world."  Excuse me -- "in fact" ??? Another example of  geologists so swept along by their own hubris that they do not know the difference between a fact and a theory. 

The detailed geological analyses (using a number of different techniques) are interesting and informative,  and there is persuasive evidence that Altar Stone samples or Xray readings are substantially different from the majority of studied samples from the ORS of South Wales and the Borders.  Special emphasis is given in the study to the high concentrations of baryte (average over 2750 ppm)  in Altar Stone samples or proxies, as against much lower values in the 58 samples analysed from the ORS outcrops in the Anglo-Welsh Basin.  Only four samples out of 58 ORS samples had barytes concentrations over 1000 ppm. (The highest reading from an ORS sample was 2665 ppm.)   Those four samples, from widely scattered locations, were carefully examined, and they were found to have lithological and geochemical characteristics that were markedly different from the Altar Stone samples.  On this basis the authors concluded that the Altar Stone was probably not derived from anywhere within the area portrayed in their Figure 1.

It has to be pointed out that that conclusion is wildly premature, since it is simply not well enough supported by the evidence base.  Only 58 ORS samples from the map area have been analysed, and there has been hardly any new fieldwork.  Altar Stone readings show Ba concentrations across a wide range, from below 1000 ppm to almost 6000 ppm, suggesting to me that BA may not be a very reliable indicator.  Outcrops from across thousands of square kilometres of "candidate territory" have simply not been sampled at all, and the database shows that there are vast variations in lithology and geochemistry within the areas of outcropping sandstones.  The problem is a common one -- too much speculation and not enough evidence.

Case not proved.

In the latter part of the paper, where the authors speculate on other parts of the UK from which the Altar Stone might have come, they use stream sediment Ba concentrations as an indicator of "candidate locations."  By their own admission Ba concentrations in stream sediments can also be related to the presence of igneous bedrock -- so this is essentially a worthless exercise which need not take up any more of our time.  If we are to take any other Ba readings seriously, they must come directly from candidate sandstone outcrops.

I am interested in the manner in which the press release that goes with this article encourages people to think that the new research shows the possibility of human stone transport over a distance of 682 miles.  From Orkney!! Oh dear oh dear.......

Finally there is a section containing speculation that the Altar Stone "arrived" at Stonehenge later than the other bluestones.  Quote:  Because of its size the Altar Stone would have looked at odds amongst a ring of smaller bluestones so a possibility, to explain its anomalous characteristics, is that it arrived at a different time and from a different source area to the bluestones. ‘De- classifying’ the Altar Stone as a bluestone frees up thinking regarding a potential source for the stone and has led us to consider that it is an appropriate time to broaden our horizons, both geographically and stratigraphically in our search for the source of the Altar Stone.   

Quote ".....we propose that the Altar Stone should no longer be included in the “bluestone” grouping of rocks essentially sourced from the Mynydd Preseli."

This is of course all nonsense. First of all, the geologists define the term "bluestone" so narrowly that it excludes all the inconvenient foreign clasts at Stonehenge, and now they want to define it even more narrowly so that it excludes anything that does not demonstrably come from Mynydd Preseli.  This is not the way to do science.  It's bad enough that the authors of this article completely ignore the possibility of glacial transport or other transport mechanisms, but we are now into the theatre of the absurd.


PS.  29.09.2023.  Sorry -- I was mistaken as to accessibility.  Neither of these articles is easy to get at.  "Treasures in the Attic" can be found if you hunt for it, here:
You can get a draft version as a download.

The Altar Stone paper is behind a paywall, and you can get at it if you are prepared to pay $25 for the privilege.  In such a fashion articles full of dodgy science are protected from effective scrutiny.


Steve Hooker said...

I received an email...

"If it were sourced in Orkney, ancient builders may have dragged the six-ton rock across roughly 682 miles. 'Monoliths used in the construction of stone circles are usually locally derived,' scientists added.

'It is the long-distance transport of the bluestones that makes Stonehenge of particular interest. The bluestones in fact represent one of the longest transport distances known from source to monument construction site anywhere in the world.'"


It's a house of foolish cards, which is looking more and more precarious.

A TV programme exposé is not far away. IMHO.

BRIAN JOHN said...

As I said, we are now in the theatre of the absurd. I am amazed that there are senior archaeologists out there who seem to be prepared to put up with this nonsense. Mind you, I have been saying that for a decade or more........

A Gee said...

We thought the difficulties of transport up the tidal Severn Estuary were bad enough, But the Pentland firth? oh please.

BRIAN JOHN said...

Nothing deters this lot. Over the years they have become specialists in the invention of headline-grabbing "discoveries" based on the flimsiest of evidence.

David Nash said...

Hi Brian. Belatedly following up on your comment: " is even more unscientific to ignore the vast numbers of smaller bluestone (i.e. foreign) clasts in the Stonehenge landscape simply because they are inconvenient."

Can you point me in the direction of any papers that discuss or map smaller bluestone clasts in the Stonehenge landscape. Bluestones aren't my thing at all, so I'm genuinely interested. I know they pop up in some archaeological digs - is that what you are referring to? Anything beyond archaeological contexts? Thanks

BRIAN JOHN said...

Hi David -- good to hear from you! I don't think anybody has thus far taken on the task of properly analysing the small fragments, pebbles and cobbles found at Stonehenge -- and that's a great pity. In their many geological studies of the Stonehenge "debitage" Rob Ixer and Richard Bevins and colleagues refer many times to the many thousands of bits and pieces they have analysed, but because they only place a value on the fragments that are linked to present or past "bluestone" monoliths they simply ignore anything that does bot fit their very arbitrary definition of a bluestone. We have no idea how many fragments have simply been labelled as "adventitious" and thrown into the rubbish bin. But we know from various references in their papers that the fragment collections from Stonehenge digs include at least 46 different rock types, as mentioned on various posts on this blog. Have these all come from "bluestone quarries" ?? I think not. But they all seem -- almost exclusively -- to have come from the west, which is why I think that ice might well have been involved.

Another cause for regret is that the geologists hardly ever talk of stone shapes and sizes -- and seem to suggest that all of the fragments studied are sharp-edged chips derived from the destruction of the monoliths by human beings. How many of them are pebbles with rounded edges? How many of them are cobbles? How many of them are small boulders like the "Newall Boulder"? How many might be remnants of ancient glacial or glaciofluvial deposits?

The most careful and objective work, in my view, is contained in the big volume (1995) edited by Ros Cleal and others -- but even in that volume I found myself irritated occasionally by the assumption that there was an "arrival date" for the bluestones -- so fragments of bluestone in sediments were almost always assumed to be proxies -- with sediments above the fragments being younger and sediments below being older. Sometimes this led the authors to get themselves into a bit of a pickle..........

There is a doctorate thesis for somebody or other, waiting to be done. And the sooner the better!

Tony Hinchliffe said...

Now Aberystwyth University ( probably Richard Bevins) say the Altar Stone's origins " could be from northern parts of the UK" (BBC Text Service, 17th October 2023). I assume the BBC is just picking up on Brian's Post.....I