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Wednesday 29 July 2020

The Stonehenge sarsens -- did they come from Overton Down / West Woods? On this evidence, probably not.

The main map from the article, showing the sarsen sites sampled.

Oh dear oh dear.  The hype has already started, on the BBC -- and tomorrow there will be a flood of similar stuff from the press:

Mystery of origin of Stonehenge megaliths solved

So -- another Stonehenge technical paper which looks impressive but which has its fair share of defects.  Of course, it is now being given the full media hype as another "groundbreaking study" which supposedly solves yet another of the great Stonehenge mysteries, but it is in reality yet another piece of assumptive research, containing exactly the sort of interpretative inflation that Gordon Barclay and Kenneth Brophy were so concerned about, a few weeks ago.

Gordon J. Barclay & Kenneth Brophy (2020): ‘A veritable chauvinism of prehistory’: nationalist prehistories and the ‘British’ late Neolithic mythos, Archaeological Journal,

DOI: 10.1080/00665983.2020.1769399

Here are the details about the eagerly anticipated new paper:

D. J. Nash, T. J. R. Ciborowski, J. S. Ullyott, M. P. Pearson, T. Darvill, S. Greaney, G. Maniatis, K. A. Whitaker, Origins of the sarsen megaliths at Stonehenge. Sci. Adv. 6, eabc0133 (2020).


The sources of the stone used to construct Stonehenge around 2500 BCE have been debated for over four centuries. The smaller “bluestones” near the center of the monument have been traced to Wales, but the origins of the sarsen (silcrete) megaliths that form the primary architecture of Stonehenge remain unknown. Here, we use geochemical data to show that 50 of the 52 sarsens at the monument share a consistent chemistry and, by inference, originated from a common source area. We then compare the geochemical signature of a core extracted from Stone 58 at Stonehenge with equivalent data for sarsens from across southern Britain. From this, we identify West Woods, Wiltshire, 25 km north of Stonehenge, as the most probable source area for the majority of sarsens at the monument.

Underlying assumptions:

1.  The sarsens were "sourced" (ie collected from) a single provenance area at some distance from the monument.

2.  There were originally c 80 sarsens at Stonehenge, of which only 52 remain.

3.  There was some ritual or political motivation for the sourcing of the sarsens which "overrode" or rendered undesirable the collection of monoliths from within the Stonehenge landscape.

4.  The sarsens could not possibly have been moved by any other mechanism than that involving human effort and ingenuity.

5.  Since the sarsens must have come from one source locality, all "inconvenient" research anomalies and outliers on graphic plots can safely be ignored.

These assumptions should have been scrutinised by the authors of this article, but they are not.  Even more extraordinary, the fundamental question "Could the Stonehenge sarsens have been sourced locally?" is not even asked, let alone answered.  The paper is hugely devalued as a result.

So what have the researchers actually done?  Well, first they made non-intrusive or non-destructive PXRF chemical analyses of all 52 sampled Stonehenge sarsens.  Quote:  Ten of the PXRF analyses at the monument record anomalously low Si (see Materials and Methods), which most likely indicates that nonquartz accessory mineral grains were excited by the x-ray beam during data acquisition. These readings are excluded from subsequent statistical investigations.  I'm always suspicious when inconvenient sampling results are rejected without adequate explanation; if there were non-quartz accessory mineral grains in ten samples, might that not indicate that they were chemically different from the others, and from a different source area?  Next, linear discriminant analysis (LDA) and Bayesian principal component analysis (BPCA) were used to analyze the PXRF data. BPCA was chosen over standard principal component analysis (PCA) for a number of technical reasons which I did not find entirely convincing.  The LDA results (in Fig 2A) show quite a wide scatter of points within and outside the 95% confidence ellipsoid, but only three stones (26, 156 and 160) are identified as being chemically distinct from the rest of the monument.  They are certainly the outliers on the diagram, but there are many other points that are chemically less distinct but which have differences assumed to be insignificant.  They might also point to different source areas.   I'd like some input on this from other experts in this field.  The point clustering shown in Fig 2B (for the BPCA analyses) is stronger, but again there are many outliers that the authors have chosen to ignore.  It's a bit difficult to see what is going on here -- some figures and tables are only presented in the "supplementary information" which can only be accessed via another hyperlink.........  At any rate, the overall conclusion is that 50 of the 52 analysed Stonehenge sarsens belong to one geochemically similar group, and that only stones 26 and 160 are "distinctly different."

Next, material from stone 58 (the one that was cored in 1958, only for the core to be lost and then found again) was studied in more detail, leading to the conclusion that it was "chemically representative of the majority of sarsens at Stonehenge."

Back to Nash et al.  Extended Quote:

For there to be a permissible match between the immobile trace element signature for Stone 58 and a potential source area, we argue that all the trace element ratios for the Phillips’ Core must lie within the limits of instrumental uncertainty of that area. As shown in Fig. 3, the geochemical signature for the Phillips’ Core exhibits a poor match for all sites beyond the Marlborough Downs (sites 7 to 20 on Fig. 1), with disparities evident for two or more of the 21 trace element ratios calculated for each site. It is therefore highly unlikely that Stone 58 was sourced from these areas. On the same basis, we can discount five of the six sampling localities within the Marlborough Downs (sites 1 to 5) as potential sources; this includes Piggledene, identified previously as an unlikely source region on the basis of heavy mineral analyses (11).

The remaining site, West Woods, in the southeast Marlborough Downs, yields permissible matches for all median immobile trace element ratios from the Phillips’ Core; this includes Pr/Zr, U/Zr, and La/Zr, which fall within instrumental uncertainty. We can therefore conclude that, based on our data, Stone 58 and, hence, the majority of the sarsens used to construct Stonehenge were most likely sourced from the vicinity of West Woods. Archaeological investigations and further detailed sampling of sarsens from West Woods and surrounding areas are now required to more tightly constrain the precise source area(s) and identify prehistoric sarsen extraction pits.

In other words, when the measurements for the "Phillips core" of stone 58 (note that we are talking about just one stone chosen to represent all of the Stonehenge sarsens) are set against the measurements for about 60 sarsen stones from 20 localities (ie 3 boulders per site)  in other parts of southern England-- including South Downs, North Downs, East Anglia and Dorset -- the best match is from three stones sampled at West Woods.  Even on the West Woods graph not all of the stone 58 points fall within the "pink zone" of instrumental uncertainty.  One might argue that the "pink" zone is unusually large for this sample, possibly showing more internal variability than in some of the other stones sampled.  One of the Essex samples (Gestingthorpe 1) is almost as good a fit, sample 7 from Mutters Moor in Devon is close, and sample 11 (from Bramdean, Hants) is pretty close too. (7.8.2020 -- text corrected.)

The West Woods representation, showing (in the pink zone) an unusual instrumental uncertainty in the measurements taken.  In other words, the pink band is wider.  This of course makes it more likely that there will be an overlap with the Stone 58 representation, shown by the points on the black line.

I appreciate that this sort of sampling is sophisticated and difficult, and that the statistical analyses are also complex,  but if the authors had taken maybe half a dozen of the Stonehenge graphs and shown them as a shaded data range (instead of using just stone 58 and deeming it to be "typical") the overall results would have looked very different.

As it is, the gigantic conclusion that the Stonehenge sarsens probably came from West Woods is based upon a matching of just four stones -- stone 58 at Stonehenge (assumed to be "typical" of all of the sarsens there) and three sampled stones in West Woods (also assumed, without any associated research, to be "typical" of the sarsens there).  Not sure what a statistician would make of that, but I venture to suggest that he would not be impressed........

Rolling on towards the end of the paper, the discussion following the presentation of the research results is best forgotten about, since it is so replete with assumptions and fantasies (for example concerning motivations, extraction options and haulage transport routes) that it devalues what was, up to this point, quite a serious academic paper.  It's another classic piece of myth promotion or interpretative inflation, or however you want to put it.


It's very useful to have this research for the "other" sarsen areas and to see how these compare with the Marlborough Downs sarsens, and so from that point of view the paper is worthwhile.  But I don't like the  assumption that the outliers in the Fig 2 diagrams are "insignificant"; I don't like the authors' interpretation that 50 of the Stonehenge sarsens have a common provenance;  I don't like the assumption that stone 58 is the best representative of the whole group of Stonehenge sarsens; I don't like the graphical representation method chosen; and I certainly don't agree with the authors that West Woods is the "most likely" site from which the great majority of Stonehenge sarsens was sourced, since the evidence is just not strong enough to say that.

In summary, an interesting paper spoiled by its own assumptions and leaving us not much better off than we were before on the origins of the Stonehenge sarsens.  And why on earth did the researchers not even bother to investigate whether the sarsens could have come from within the Stonehenge landscape?


We can already see on the press coverage that the authors' "most likely" statement has been transformed into something quite definitive -- and no doubt this will have been encouraged in the press release that has come from the University of Brighton.  So we see the Stonehenge myth machine in top gear, with interpretative inflation completely unchecked.   Sad -- but did we really expect anything different?

There is a short popular article by Nash and Darvill here:

Nothing subtle about this -- for the purposes of public consumption, the origin of the sarsens is now sorted, at the expense of academic rigour or caution.........


Tony Hinchliffe said...

From my quick speed reading of the Paper, the researchers did investigate some of the sarsens still extant in the Stonehenge area.

BRIAN JOHN said...

Of the 20 candidate sarsens analysed, none were from the Stonehenge area -- except for the 52 stones actually at Stonehenge.

chris johnson said...

Hot news. Heard about this in NL this evening (RTL news) and checked here immediately. Great inputs Brian!
It will no doubt succeed to be a 7 day wonder of a story - wonder what Myris thinks or is he one of the authors?

Steve Hooker said...

I thought there are at least two types of sarsen at Stonehenge. One's purple, one's orange. Maybe tourmaline, maybe iron based. A quick look at the paper doesn't mention orange nor purple. Oh well.

And surprised the Heel Stone is of the same type as the rest. Interesting. As there's a hole where it was thought it was pulled up from, close by.


BRIAN JOHN said...

I too was intrigued by that, Steve. There have been lots of discussions about the differences in appearance of different Stonehenge sarsens. I think the researchers ignored those -- they were intent on a "lumping" exercise designed to show that nearly all of the 52 Stonehenge stones sampled belonged to a single group.

Tony Hinchliffe said...

This morning on Breakfast BBC their intrepid reporter told us that ANOTHER CORE STONE has since turned up in 'the Museum down the road, they did not know they had it' this Story no doubt has Legs on it, maybe after all some of the Stones are from Ireland or the Isle of Man.

At least BBC Points West from Bristol merely said the bluestones originated from Pembrokeshire, whereas our Intrepid Hero on main BBC News wanted to have us accept that "We've known since 1923 that the bluestones were brought from Wales". On such statements are myths perpetrated.

BRIAN JOHN said...

Myths everywhere. Maybe we should remind all those who believe everything they read in the Mail and the Sun that this piece of provenancing is based on matching ONE sarsen from West Woods with ONE sarsen from Stonehenge -- and the match is not perfect. Hmmmmm.........

Tony Hinchliffe said...

Are myths perpetrated? Possibly. More often, perpetuated.

Is it just the Mail and the Sun that over - simplify this. What about, e.g. the Guardian and the Independent.

BRIAN JOHN said...

Crimes are usually perpetrated -- but I think, on consideration, this this word is quite Ok here, since those who perpetuate or promote myths are also guilty of criminal negligence. The human transport / quarrying / proto-Stonehenge myth is also underpinned by scientific malpractice -- so there is more than a hint of "criminality" there. I rest my case. M'Lud.........

ND Wiseman said...

Hi Gang,
The paper mentions 52 Sarsens were examined at The Hedge. It goes on to mention that 50 match their studies. This leaves out S-54 & S-56, as they are the 'Orange' ones.


BRIAN JOHN said...

Why would they leave out the orange ones, Neil? They claim to have sampled ALL of the Stonehenge sarsens.

Steve Hooker said...

I made a map of known orange and purple sarsens. Hope it helps

BRIAN JOHN said...

Thank you Steve -- that's very interesting. May I please publish it?

BRIAN JOHN said...

Thank you Steve -- that's very interesting. May I please publish it?

ND Wiseman said...

Hi Brian
There were 52 Sarsens tested / 2 didn't match the rest = 50.
My assumption that the two left-overs were 'obviously' S-54 & S-56 is now clarified as incorrect. The outcasts are -60 and the three chunks of -160.


PS: Happy Birthday

BRIAN JOHN said...

Now I am confused, Neil. The authors -- and the diagrams -- mention stones 26, 156 and 160 as the "outliers" which appear to have a different geochemistry. Have they subsequently said that those labels were incorrect? I don't recall any mention of stone 60. They also said that on further analysis stone 156 was within the "geochemically similar" group, leaving just stones 26 and 160 as the aberrations.

Kosta Dean said...


If the presence of 'rubbish' sarsens at Salisbury Plain is in the absence of any "thick Palaeogene host sands" at Salisbury Plain, wont these sarsens then be erratics?

And if these erratic 'rubbish' sarsens were to match the Stonehenge sarsens, wont that make these monoliths also erratics?

BRIAN JOHN said...

As I understand it from David Nash's comments, there is at least one more paper on the way relating to this issue -- but he seems pretty convinced that there was NOT a sediment bed thick enough and sandy enough over Salisbury Plain to have given rise to abundant rectilinear lumps of silcrete lying about in the landscape. It remains to be seen whether that confident assertion stands up. And yes, the fact that there are SOME big lumps lying around has to be explained, quite possibly by natural processes as described by Peter Worsley in his recent paper. One of my gripes about the new paper is that it is underpinned by an assumption that wherever the monoliths came from, human beings did not just the gathering but the moving too.....