Sarsen sources and instrumental /analytical uncertainty

In the midst of all the media celebrations about the solving of the great sarsen stone mystery, I'm quite intrigued by some of the comments from quite senior academics in Twitter conversations with David Nash. There seems to be more or less universal praise for the research, which suggests to me that nobody has actually read the article properly, and that academics have simply been reacting rather lazily to the press coverage and the items broadcast on the BBC, ITV,  and Sky.

I am really the only person concerned about the following?

Ref:  Nash et al, 2020: https://advances.sciencemag.org/content/6/31/eabc0133

1.  No attempt is made to explore the possibility that the Stonehenge sarsens were all picked up from the chalklands of Salisbury Plain.  (Instead, for some reason, areas like the North Downs, the East Anglian Heights, and Dorset were treated as higher priorities.)

2.  The conclusion that 50 of the 52 Stonehenge sarsens are from one common source is not adequately supported by Figure 2 of the paper, since only some of the 260 data points (5 readings were taken from each stone) are identified, and there are many "outliers" which are simply ignored.  I have been unable to access the full data sets and supplementary materials -- I don't know why. (I don't have a problem with most of the Stonehenge sarsens having a shared geochemistry -- that's what one would expect if the stones were picked up locally --  but it would be good to know just how wide the variability is, rather than just being told that 50 of the sarsens have come from a single source.)  Here is the link, if anybody else wants to try: http://advances.sciencemag.org/cgi/ content/full/6/30/eabc0133/DC1

3.  The "matching" of the Stonehenge sarsens to the sarsens of West Woods is dependent upon the examination of just ONE sarsen from West Woods and just ONE sarsen from Stonehenge.  This is completely unsatisfactory, as the authors of the paper must know.  And yet they have claimed that "most of the sarsens at Stonehenge have come from West Woods."

4.  I'm worried that the plotting of the trace element data for stone 58 and for the 20 sampled sarsen sites does not involve a direct "like for like" comparison.  This is because the core samples were done on rock taken from deep within the sarsen stone, while the other measurements were from non-invasive surface readings.  I would like to know how this might have affected the information plotted.

5.  The plot of trace element ratio data for West Woods is used by the authors of the paper as the "killer fact" that establishes beyond all reasonable doubt that the Stonehenge sarsens came from this site.  And yet, when we look at it carefully, its value is very limited indeed.

 

On this plot, the black line plots the ratios measured from the "missing but now found" core from stone 58.  The little cross bars show the range of uncertainty in the readings.  The pink band shows the range of instrumental / analytical uncertainty for the same trace elements at the selected site.  But note that the scale of this uncertainty here is the third highest of all the sarsen stone readings (only Monkton Down and Totterdown Wood have greater uncertainties).  This means that the validity of the main conclusion (namely that West Woods provides the best match) has to be questioned.  If the scale of the uncertainty had been just a little less, then the pink band would have become a thin pink line, and so many readings would have been adrift that West Woods would not have been a favoured candidate source at all.  Just look at the figure showing all 20 sites:

With less uncertainty (ie a thin pink line instead of a broad band) at West Woods, the best candidates for the "sarsen stone source area" would be the samples numbered 3, 4, 7, 11, 12, 13, 14, 17 and 20.  That is, nine other sites would have had equivalent or better fits...............

Sarsens in West Woods (Marlborough News)

I repeat -- the conclusion that the Stonehenge sarsens came from West Woods is not adequately supported by the data.

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Note added 7th August 2020:  Since this post is still getting lots of hits (590 so far, and counting) and since most readers will not have the stamina to read more than 50 discussion contributions, this is the state of play:

Point 1.  This is still a matter of concern
Point 2.  Lead author David Nash is adamant that 50 of the Stonehenge sarsens are from a common source, and that the scatter seen on Fig 2 of the paper is down to natural variation within samples.    I'm still not convinced.  Further research will no doubt reveal the truth.
Point 3.  I'm happy to correct this.  In fact THREE stones from West Woods were sampled.  I was misled by an error in the paper (now acknowledged by David) which referred to "20 field samples" (ie one from each of 20 sampled field locations) when it should have referred to "60 field samples" (ie three sampled boulders in each location).  I should have checked this out in the Supplementary Data files, but initially had problems accessing them.  Anyway, apologies for that mistake.
Point 4.  Again, my mistake.  I was misled by some ambiguous wording in the paper to believe that ALL of the sampling was non-invasive.  In fact the non-invasive sampling was done just at Stonehenge (the stones are deemed too precious to harm in any way), while the stones from other sites were investigated via rock samples taken to the lab.  I should have read the paper more carefully.  There was a "like for like" comparison of the stone 58 (Stonehenge) core with the 60 or so samples taken from other locations.
Point 5.  David claims that the West Woods trace elements ratio graphic is as close to a perfect match with the data from core 58 as it is possible to get.  He also says that a perfect match would only be proposed if ALL of the element ratios overlap on the graphic.  To me, it looks as if one of them (Uranium?) doesn't overlap, but that may be down to my fuzzy computer screen.......  At any rate, I haven't changed my view that the best we can currently say is that "Of the 20 potential sarsen provenencing sites so far investigated, West Woods provides the best match, and on current evidence it is the most likely source for the bulk of the Stonehenge monoliths."  That is very different from saying "We now know where the Stonehenge sarsens came from."

Additional Note 10th August 2020.  David is very upset again, and claims that I am misrepresenting him.  In point 2 I used inverted commas around the words "scatter" and "natural variation" -- as I often do without any disrespect or cynicism.  If the word "cluster" is acceptable, I am not sure why there is a problem with the word "scatter."  Anyway, I have now removed the offending inverted commas, and hope that that will make him happy.  Time will tell whether the 50 Stonehenge sarsens are from exactly the same source, and whether there are other variables (as yet unidentified) that affect PXRF readings. (In my time, I have seen many wonderful new techniques being used.  Initially they are all believed to provide "correct" information -- until, later on, the correction factors kick in, and interpretations and conclusions have to be revised, sometimes very dramatically........)   Next, David is upset that I mention "some ambiguous wording" in my point 4.   This is getting ridiculous, and I'm getting fed up.  Almost all papers contain phraseology that could have been better, and this one by Nash et al  is no exception.   The last paragraph of the Introduction should have referred to "rock samples taken from a representative range of sarsen boulders" to make it clear that an invasive technique was involved.  And OK -- if David tells me that there is an overlap on the graphic for the U element ratio, I'll take his word for it.

It's a bit rich that David bangs on furiously about my "misrepresentations" of his scientific research, but cannot even bring himself to apologise for his own mistake in referring in the paper to 20 field samples of sarsen when the figure should have been 60.  Just a typo?  Hmmmm...

On everything else we will agree to differ, and if David wants to say anything else he can say it elsewhere.

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

https://www.bbc.co.uk/news/uk-england-wiltshire-53580339

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).

ABSTRACT

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.

https://advances.sciencemag.org/content/6/31/eabc0133

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."

https://www.archaeology.co.uk/articles/getting-to-the-core-of-stonehenge.htm

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.

CONCLUSION

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?

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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?

https://www.independent.co.uk/news/science/archaeology/stonehenge-stones-sarsen-archaeology-a9644436.html

https://www.theguardian.com/uk-news/2020/jul/29/archaeologists-discover-source-stonehenge-giant-sarsen-stones

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

https://theconversation.com/stonehenge-how-we-revealed-the-original-source-of-the-biggest-stones-143564

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.........

Thank you for the birthday greetings!

Nothing to do with Stonehenge or the Ice Age -- just old age!  But herewith some grateful thanks for the cheery greetings I received yesterday, from assorted old friends of this blog, on reaching the ripe old age of 80.  Much appreciated, folks!  We had a quiet day, with just our son Martin over from Somerset -- but we did enjoy an excellent rainbow trout for supper, a rather fine zoom session with our nearest and dearest from assorted parts of the globe, together with many video greetings from old friends.  These modern whizzo gadgets are sometimes rather useful.

Today, back to normal, with house cleaning, gardening, repairing the paving in the back yard, and showing some potential buyers around the house and grounds.  So life goes on........

Another aurochs horn

The aurochs horn found recently in the Severn Estuary.  It's a nice one, but it's not quite as big as it looks in the photo.  A lucky find -- it was embedded in the mud and is very well preserved.  Pic: Martin Morgan.  Further info here:

https://www.walesonline.co.uk/news/wales-news/horn-extinct-creature-died-around-18329016?fbclid=IwAR3zyOrHWuuWouihXJfJMlBMYVkP4_ZIufzmJkQhLlUEdaUX5GFnIb0q628

Geological Notes on the Altar Stone paper

An EH photo of the surface of the Altar Stone, visible between fallen sarsens 156 and 55b (trilithon 55 is broken into two portions of almost equal size.)  There are some doubts about its dimensions -- most references quote approx 4.9m x 1.5m x .5m -- but one EH publication refers to it as being 3m wide, which means it should be referred to as a slab and not a pillar.

An extract from Anthony Johnson's excellent plan of the Stonehenge stones.  The Altar Stone is stone 80, with two sarsens lying across it.  

Geological Notes on the Altar Stone paper

It’s good to get some comments from another geologist who has actually studied the Altar Stone and the Devonian sandstones of West Wales. I’ve been in correspondence with Richard Thomas, who now lives in Newfoundland, for some years. Last time he visited Wales, he managed to fit in a visit to Rhosyfelin as reported here: https://brian-mountainman.blogspot.com/2018/04/another-rhosyfelin-sceptic.html

Key stratigraphic and lithological information is here:
http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=COB

This is the paper being discussed:

Constraining the provenance of the Stonehenge ‘Altar Stone’: Evidence from automated mineralogy and U–Pb zircon age dating.
Richard E. Bevins, Duncan Pirrie, Rob A. Ixer, Hugh O’Brien, Mike Parker Pearson, Matthew R. Power, Robin K. Shail
Journal of Archaeological Science 120 (2020), 105188

Here are some of Richard’s points:

I found the paper very interesting, and we should commend Rob Ixer and Richard Bevins for all the hard work they have put into the provenancing of the Altar Stone.

I have suggested to the authors that there are two fundamental provenancing issues:

(1) the epic task of unequivocally identifying the parent formation and source location of the Altar Stone (Stonehenge Stone 80);

(2) proving whether or not the sandstones comprising the Altar Stone and the so-called "Altar Stone debitage" are indeed one and the same -- i.e., were derived from a single, lithostratigraphic source unit. Neither issue can be completely resolved unless fresh samples are obtained for analysis from the Altar Stone itself.

I'm under the impression that no indisputably genuine thin sections of the Altar Stone are known to exist. As summarised by Ixer et al. (2019, p.1): "It is not certain that the Altar Stone has been directly sampled, certainly not in the last two centuries, and all samples labelled Altar Stone in museum collections appear to be from loose fragments/debitage and designated as 'Altar Stone' by 19th- and 20th-century excavators." However, in an earlier paper, Ixer and Turner (2006, pp. 2-3) state that: "...the thin section labelled '277 Altar Stone Stonehenge' is ....the only piece of the monolith available for investigation." With respect to issue (2), the various Altar Stone-related papers (including Bevins et al., 2020), contain references to the parentage of the samples described that I find somewhat confusing and, at times, contradictory. For example, on p.1: " .... mineralogical data from proposed Stonehenge Altar Stone debris..."; p.3: "..three debris samples, also thought to be derived from the Altar Stone."; p.3: "..the second type of sandstone, found as rare debris at Stonehenge as well as comprising the Altar Stone..."; p.3: "...six of which have been identified petrographically as being derived from the Altar Stone..."; p.5 (Table 2 caption): ".....samples analysed in this study from the Stonehenge Altar Stone.."; p.7: "...the samples interpreted as derived from the Altar Stone..."; p.7: "...the three Altar Stone samples..."; p.11 "...the so-called Altar Stone sandstone..."; p.12: "...study of the clay mineralogy of the Altar Stone sandstone...". In a similar vein, from Ixer and Bevins (2013, p.14): "...potential Altar Stone debitage ..."; "Three typical Altar Stone debitage lithics.."; "...it is now possible to provide a 'standard' petrographical description for the Altar Stone...”.

This seems to me to be a case of mixed messaging. Ixer and Bevins are trying to prove that sandstone samples such as SH 08, HM 13 and FN 573 are identical to, and/or derived from, the Altar Stone, but how is that possible without having an absolutely bona fide Altar Stone sample for comparison? To eliminate any ambiguity, I think all supposed Altar Stone sandstone samples should have qualifiers such as: 'suspected', 'potential', 'purported', 'possible', 'so-called', etc. added to their descriptions. Unless, of course, 277 is the real McCoy (see below).

One technical point: it's the Mill Bay Formation that is the bio- and lithostratigraphic equivalent of the Senni Formation of the Brecon Beacons area, and not the entire Cosheston Subgroup.

The key point of the paper: Ixer and Bevins have confirmed in the new paper that the analysed micaceous sandstones from the Stonehenge Landscape were not derived from the Mill Bay Fm. section at Mill Bay. The underlying, 435-550m-thick Llanstadwell Fm. also contains numerous green, highly micaceous sandstone units although personally, I don't think they're a match for the Altar Stone either.

From the location information in Ixer et al., 2020 (p.10), it's clear that sample MB3 collected by Brian John actually came from the lower Lawrenny Cliff Fm. -- which explains its compositional differences from the other Mill Bay samples. According to my old field notes, the junction between the two formations (underlying Mill Bay Fm and overlying Lawrenny Cliff Fm) crosses the HWM about 60m south-west of the Whalecwm slipway.

Regarding Ixer et al., 2019 (p.4), my macroscopic description of the Altar Stone (included in Thorpe et al., 1991) was based on me crawling over it and taking photographs (back in January, 1973). I never looked at the samples described by Huggett (1993).

QEMSCAN is a great tool -- especially when used to complement thin section optical mineralogy. The latter will still be essential for determining the Altar Stone's provenance. Using it you can quickly rule out potential source rocks. For example, it only took me a minute to realise that OU9 (444) was not a Cosheston sandstone. Likewise, as you know, verifying whether (p.7) "...quartz and albite cementation, or grain boundary dissolution may also have occurred..." would be simple in thin section. In my view, the fact that QEMSCAN 'reports' rock fragments as their constituent minerals is a major shortcoming, particularly since intraformational and extraformational lithoclasts are such a common component of most Anglo-Welsh ORS sandstones. I suspect that thin section analysis of the diagenetic histories of possible source sandstones will play an important role in unravelling the Altar Stone's provenance. Carbonate cements (including poikilotopic calcites) are common in the Senni Fm. and tend to preferentially attack certain minerals or rock fragments (e.g., K-feldspars), meaning that modal analyses can't give you a true picture of the original composition of the framework-grain fraction. Thin section work, in tandem with QEMSCAN, will be the key to identifying any given sandstone's diagnostic, compositional and textural 'signature' for comparison with those of potential source units.

Quote from P.7: "Clay minerals in sandstones may occur as a detrital matrix or as ......diagenetic cements." They also, of course, occur as claystone or fine siltstone intraclasts, and as alteration products.

Could there be any other cryptic "species" of sandstones among the Stonehenge Landscape debitage?

Is the famous slide 277 really a thin section of the Altar Stone? When I looked at this thin section, I felt that it didn't match what I'd expect a genuine Altar Stone specimen to show. This sandstone is finer grained (very fine vs. fine sand grade) and a lot less micaceous than the Altar Stone, and only contained a couple of garnets. I think it unlikely that it is a genuine Altar Stone sample.

I have no problem agreeing that the "Altar Stone" samples (Table 2; Figs. 2-5 and 8) -- especially FN 573, HM 13 and SH 08 -- share the same parentage. Again, the key question is whether they share that parentage with the Altar Stone. From an inspection of Table 2 and Fig. 2, I'm sceptical that the six numbered samples were derived either from the Altar Stone or its parent unit. Two compositional issues bother me:

(1) Thomas (1923, p.244) describes the Altar Stone's heavy mineral suite as being "exceedingly rich in garnet" which I interpret as being on a par with garnetiferous Llanstadwell Fm. and (especially) Mill Bay Fm. sandstones. However, the analyses indicate that the garnet content of the two Mill Bay Fm. sandstones is an order of magnitude greater than that of the supposed "Altar Stone" samples;

(2) the Altar Stone (from my field inspection) contains abundant muscovite -- certainly equal to the muscovite content of most 'lower' Cosheston Subgroup sandstones. From Table 2, Mill Bay 1a and 1b (average = 4.88%) contain close to double the amount of muscovite present in the six "Altar Stone" samples (average = 2.48%). I consider these differences to be significant grounds for suspecting that the latter are not of genuine Altar Stone derivation. However, this question can only be resolved when/if English Heritage allows new Altar Stone samples to be collected.

Burl (2007, p.281) gives the length, width and thickness of the Altar Stone as 5.0m, 1.1m and 0.53m, respectively. If I remember correctly, the latter's small-scale, trough cross-lamination indicates it is lying right way up stratigraphically. I'd suggest that two samples of the Altar Stone be taken: one from near the stratigraphic top of the unit and one near its base. Both sample sites would be hidden from public view (beneath the turf) because the top sample would have to be taken below the upper portion of the Stone that has been damaged/mineralogically altered by the fires lit upon its exposed surface.

Most Senni Fm. in-channel sandstone bodies that I have observed, generally fine upward. When sampling potential Altar Stone source units, it will be extremely important to ensure that the grain-size distributions of the sandstones collected match that of the Altar Stone as closely as possible, so that compositional differences related to hydraulic equivalence are minimised.

Senni Fm. sandstones vary in colour, provenance, distance from sediment source(s) and diagenetic history from West to East across the Formation's outcrop. I agree with Ixer and Bevins that the eastern portions of its outcrop are the most promising in terms of potential Altar Stone source units. It may be worthwhile checking for any fracture pattern differences across the outcrop, in order to locate joint systems capable of "releasing" sandstone blocks up to 6m long and up to 0.6m in thickness.

The zircon images and date ranges published in the new paper are fascinating! P.8: "A simple interpretation is that the Altar Stone grains reflect a more mature sedimentary environment.....". I suspect that provenance differences are a more likely explanation for the observed 'disparity' in zircon morphologies. The range in zircon morphology and their ages furnishes additional evidence of the prevalence of multicycle detritus within the Cosheston Subgroup sequence (cf. Thomas et al., 2006). The greater range of ages represented by the"Altar Stone" micaceous sandstone zircons is very interesting and suggests a geologically complex source area for these rocks and/or the availability of an abundance of second- and multi-cycle detritus.

I am a strong proponent of the glacial transport of the bluestones to a 'greater Stonehenge' catchment area rather than human transport, and consider the archaeologists' 'new' land route proposal (apparently signed up to by Ixer and Bevins) to be completely lacking in credibility. Also, during my visit to Craig Rhos-y-felin I could find no evidence in support of quarrying at the site.

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Most of Richard's observations are of a technical nature,  but it's interesting that, like me, he takes issue with the assumption that all of the supposed "Altar Stone samples" have actually come from the Altar Stone,  and like me he feels that the authors of the paper should have been much more circumspect in their wording.   We also share concerns about the promotion (yet again!) of the human transport hypothesis, and about the presumption that there is a man-made Neolithic quarry at Rhosyfelin.  On the other hand we are both happy that the "Altar Stone" samples probably do come from a common source; that the sampled debris did not come from the Mill Bay Formation;  and that the real provenance of the "Altar Stone" fragments probably lies somewhere in the eastern part of the Senni Beds outcrop, far away from Preseli.  As I have said before, ice from that area flowed on more than one occasion southwards and south-eastwards towards the Severn Estuary,  so this new work does nothing at all to dent the glacial transport hypothesis.

The Mill Bay samples

I just wanted to put on the record the approx positions of the sampling sites I visited some years ago when I gathered rock samples for Rob Ixer and Richard Bevins.  The above map is Fig 1 reproduced from the seminal paper by Richard Thomas and others:

THOMAS, R G, BARCLAY, W J, MORRISSEY, L, WILLIAMS, B P J, and ALLEN, K C. 2006. Enigma variations: the stratigraphy, provenance, palaeoseismicity and depositional history of the Lower Old Red Sandstone Cosheston Group, south-central Pembrokeshire, Wales. Geological Journal, Vol. 41, 481-536.

I have marked two sampling points on the map.

MB 1 and MB2 came from Mill Bay, close to the bend in the coast. So there is no doubt that they represent one of the facies of the Mill Bay Formation.  The other point shows a sampling point (MB3) near Whalecomb jetty.  Richard Thomas thinks that the junction between the older Mill Bay Formation and the newer Lawrenny Cliff Formation lies about 60m south of the jetty.  So I think that when I took that sample I inadvertently sampled the Lawrenny Cliff Formation sandstone near its base -- this explains the slight differences between this sample and Samples MB1 and MB2.

Nonetheless, it's fairly clear that the 3 samples are all closely related, and that they are very different from the supposed "Altar Stone" samples analysed by Ixer and Bevins and reported in their recent paper.

Erratic boulder trains and fans

Super-erratic from Scandinavia, now found on the coast of Estonia.  Weight -- approx 2,500 tonnes.

The Thunder Stone is a vast erratic of Rapakivi Granite used as the plinth for a famous statue of Peter the Great in St Petersburg.  It was found in marshy ground not far from the shore of the Gulf of Finland, and was moved to its designated place entirely by "people power" over the course of two years.  It was reputed to weigh 1500 tonnes. This granite outcrops in a number of places in southern Finland.  (Thanks to Tony for bringing this to my attention.) 

On this map from RF Flint (1957) the Rapakivi granite outcrops are numbered 3 and 5.  The "Thunder Stone" was picked up maybe 60-70 km from its source, having been transported by ice in a SE direction.

Here are some maps of erratic trains and fans from around the world.  Widely differing scales.   Note that erratic trails or trains are relatively thin but are simplified on maps by drawing a line between source and end destination.  This is misleading, since erratic travel is normally NOT direct, since ice movement directions are shifting all the time.  More realistically, a zig-zag movement should be portrayed.   The maps showing "indicator fans" are also unrealistic, since they simply show the widest possible dispersal of rocks picked up by a glacier from a singe provenance or source. This to some degree demonstrates shifting ice movement directions.  Another factor to be taken into account is that many erratic boulders have been moved incrementally over the course of several different glaciations.

Note that some erratic blocks in Scandinavia and North America have been moved over 1,000 km.  That having been said, the great majority of erratic boulders (and "super-erratics") are derived from locations less than 10 km away from the places where they are now found.

Fracture opening up on Rödlöga Storskär in the Stockholm Archipelago. Probably this coincides with a pre-existing joint in the bedrock.   If the Last Glaciation had gone on for a little longer, a giant erratic weighing 100,000 tonnes would have been dragged away southwards.

Boulder trains in Tierra del Fuego

I did some posts a few years ago on erratic entrainment and transport, and on the Darwin Boulder Train in Patagonia. The key text at the time was this one:

Evenson, E.B., Burkhart, P.A., Gosse, J.C., Baker, G.S., Jackofsky, D., Meglioli, A., Dalziel, I., Kraus, S., Alley, R.B., Berti, C., 2009. Enigmatic boulder trains, supraglacial rock avalanches, and the origin of “Darwin's boulders,” Tierra del Fuego. GSA Today 19, 4–10. http://dx.doi.org/10.1130/GSATG72A.1.
If you put "Darwin Boulder Train" into the search box you will be able to see the relevant posts.

I omitted at the time to mention this very interesting article by Darvill, Bentley and Stokes:

Christopher M Darvill, Michael Bentley, and Chris R. Stokes, 2014. Geomorphology and weathering characteristics of erratic boulder trains on Tierra del Fuego, southernmost South America: Implications for dating of glacial deposits

Geomorphology 228, pp 382-397

DOI:
10.1016/j.geomorph.2014.09.017

https://www.researchgate.net/publication/266321104_Geomorphology_and_weathering_characteristics_of_erratic_boulder_trains_on_Tierra_del_Fuego_southernmost_South_America_Implications_for_dating_of_glacial_deposits[accessed Jul 20 2020].

Abstract

Erratic boulder trains (EBTs) are a useful glacial geomorphological feature because they reveal former ice flow trajectories and can be targeted for cosmogenic nuclide exposure dating. However, understanding how they are transported and deposited is important because this has implications for palaeoglaciological reconstructions and the pre-exposure and/or erosion of the boulders. In this study, we review previous work on EBTs, which indicates that they may form subglacially or supraglacially but that large angular boulders transported long distances generally reflect supraglacial transport. We then report detailed observations of EBTs from Tierra del Fuego, southernmost South America, where their characteristics provide a useful framework for the interpretation of previously published cosmogenic nuclide exposure dates. We present the first comprehensive map of the EBTs and analyse their spatial distribution, size, and physical appearance. Results suggest that they were produced by one or more supraglacial rock avalanches in the Cordillera Darwin and were then transported supraglacially for 100 s of kilometres before being deposited. Rock surface weathering analysis shows no significant difference in the weathering characteristics of a sequence of EBTs, previously hypothesized to be of significantly different age (i.e., different glacial cycles). We interpret this to indicate that the EBTs are much closer in age than previous work has implied. This emphasises the importance of understanding EBT formation when using them for cosmogenic nuclide exposure dating.

The main emphasis in the article is cosmogenic dating, but it is also suggested that erratic transport distances are quite modest in Patagonia, and that the main erratic trains are made of rockfall debris and boulders dumped onto glacier ice in the catchment areas and then transported supraglacially.  The cosmogenic dates support the idea that the erratic boulder trains of the studied ice lobe are relatively young, and this is supported by the appearance of the erratics themselves -- they are often very large, but relatively angular, with limited abrasion traces.  (If they had been transported subglacially, a higher degree of abrasion and rounding off of edges would be expected.)  However, there were exceptions, and the authors conclude that some of the erratics with anomalous ages have probably been recycled from the erratic trains and glacial deposits laid down in earlier glaciations.

There is an interesting but brief discussion on boulder size versus distance travelled, since the assumption is that large supraglacial erratics can travel for tens of kilometres without being dramatically modified, but that that scenario does not apply to erratics carried on a glacier bed.  Glacier modelling suggests that erratic breakage and comminution are key processes on the glacier bed, and the authors test this by citing ten other studies of erratic boulder trains from across the world.  Their graph (Figure 2) is not particularly helpful, partly because it is seriously lacking in data.  But all credit to the authors for trying to sort this out.  They say:

o

"..........our synthesis of previously published data suggests an apparent trend between transport distance, boulder size, and the proposed transport pathway (Fig. 2), with those moved greater distances (e.g. N~10 km) more likely to have been transported supraglacially. The relationship with boulder size is unsurprising given the association between transport pathway and boulder erosion (Boulton, 1978), but is important in the context of er- ratic dispersal more generally. For example, the principles of ‘half-dis- tance’ transport (Salonen, 1986) and concentration peaks (DiLabio, 1981, 1990; Boulton, 1996) may better relate to subglacial EBTs, where- as supraglacial EBTs are also controlled by the maximum transport distance and the preservation potential of the boulders."

Clearly this work has considerable implications for our considerations of the "bluestone erratic train" stretching from Preseli to Salisbury Plain.  Most of the bluestones at Stonehenge are abraded and weathered boulders -- as one might expect of material carried within or beneath a glacier.  But the monoliths that are shaped more like pillars are more difficult to explain.  Did they travel as pillars without being broken, or are they remnants of larger slabs or pillars? Most of the pillar bluestones have been shaped in the Stonehenge landscape by the people who found them and used them -- was that fashioning cosmetic, or quite dramatic in scale?  There is certainly enough bluestone "debitage" to suggest quite extensive working.   I have already done many posts on this topic.

This paper by Darvill et al is an interesting contribution, but there are abundant erratic boulder trains all over the world that they have not considered and which might allow interesting insights.  Also, the authors do not consider englacial transport mechanisms.

Ice does sometimes move by shearing, and debris does get lifted from the glacier bed towards the ice surface when it flows across basal ice that is blocked by transverse obstacles. Even without shearing, in areas of compressive flow within a glacier, erratic blocks and smaller debris must be lifted off the glacier bed and carried up into the body of the glacier for transport downstream.  Abrasion on a glacier bed is favoured by basal melting, which renews the "tool load" on the bed.  But the process of entrainment is a complex one, and even without regelation (the addition of ice layers on a glacier bed) if large plucked blocks of bedrock are not entrained of lifted off the bed, the basal debris load would become so thick that further erosion would become impossible.  And in every glaciated area we find deep bedrock hollows which are "clean" in the sense that the rock that once occupied them has been removed and quite literally lifted away.

This is an idealised diagram showing how ice flow in a glacier may carry ice (and debris) upwards towards the surface (compressing flow) or downwards towards the bed (extending flow).  We do not need to invoke actual shearing -- but it may occur.  This is for an idealised small glacier with a steep gradient.  Stretch it out to an ice stream more than 200 km long with a very gradual gradient or a flattish surface long profile (as in the case of the Irish Sea Ice Stream) and things become more complex and more subtle, with topography and the nature of pre-existing bottom sediments becoming more important.  But the same principles apply -- where there are obstacles or upslopes, there will be compressive flow, carrying erratic boulders and finer debris up into the body of the glacier and maybe even up onto the ice surface.  But if the area concerned happens to be above the equilibrium line (ie in the accumulation zone) the debris will immediately be buried by accumulating snow and firn, and incorporated into the body of the glacier.  

Ice that flows in constrained troughs (think Sognefjord and Nordvestfjord) flows UP reverse slopes as it approaches downglacier thresholds or if erosive power is lost because of diffluence.  As studies of intensively-glaciated terrain continue in Antarctica and Greenland, it is clear that ice erodes deeply and transports or evacuates erratics and debris UPSLOPE for considerable distances in closed troughs and in many other situations.  It is unrealistic to assume that the millions of tonnes of debris removed are all transported on the glacier bed.

Long profiles of glacier troughs, showing the depth of the trough floor beneath msl.  Above, Sognefjord, and below Hardangerfjord -- both in Norway.  Note that the floor of Hardangerfhord rises irregularly, because diffluence occurred across many cols and through distributive troughs in relatively low-lying coastal terrain  In Sognefojord supplemental inputs of ice from tributary glaciers enabled the Sognefjord Glacier to keep on "digging" until it was near the edge of the uplands -- at which point there was large-scale diffluence, and the glacier bed rose by 

about 1000m in just a few km.

https://brian-mountainman.blogspot.com/2017/01/on-uphill-transport-of-debris-by.html

https://brian-mountainman.blogspot.com/2020/01/strandflats-skerries-archipelagos-and.html

https://brian-mountainman.blogspot.com/2017/01/more-on-closed-subglacial-troughs.html

The debate continues........

The ability to knowledgeably question

The forgotten art of scrutiny.......  Thanks to Tony for posting this pic on Facebook.  The perfect illustration for this post!

Twenty-five years ago, Carl Sagan referred to a “slide back into superstition” of the religious variety and also a general "celebration of ignorance," such that well-supported scientific theories carry the same weight or less than explanations made up on the spot by authorities whom people have lost the ability to “knowledgeably question.”

The other day, I added this as a postscript to another post:

I like Sagan's reference to people who "have lost the ability to knowledgeably question" the so-called authorities who tell them things or sell them ideas. That is indeed a social epidemic, and a very dangerous one. I see the results almost every day, on blogs and in Facebook groups which I follow intermittently -- whenever a spectacular headline appears in the press following a press release relating to Stonehenge, we see a flood of comments showing that people are completely fooled by the snake oil salesmen, with hardly anybody going back to the recently published article itself and subjecting it to critical scrutiny. Why don't they do that? The reasons are many and varied -- but it's clear that people are intimidated by articles that have graphs and tables in them and by writing that is often far more complex than it needs to be.  And yes, one has to conclude that most members of the public no longer have the instinct or the ability to examine a text and work out for themeselves that what they are reading is complete tosh.

I have been looking at Wikipedia lately, and have been horrified by the extent to which the "volunteers" who manage the site are fooled into thinking that wildly speculative archaeological theories are actually factually based and "true" -- and by the blithe acceptance of press releases and newspaper articles as "supporting publications".  I know that Wikipedia depends upon its readers and volunteers for scrutinising the things that powerful vested interests place there, on the record --  but it seems to me that more and more fantasies are appearing on Wikipedia, to be accepted by gullible readers as "the truth."  So where are those who should be doing the "knowledgeable questioning"?

Maybe this is not something treated as a priority in modern universities?  

When this lack of scrutiny is coupled with the "celebration of ignorance" which we see in the mainstream media and in popular culture, we have a problem.    Another quote from Sagan:

The dumbing down of America is most evident in the slow decay of substantive content in the enormously influential media, the 30 second sound bites (now down to 10 seconds or less), lowest common denominator programming, credulous presentations on pseudoscience and superstition, but especially a kind of celebration of ignorance”

The wicked Dr Kurdling to Master Molesworth after delivering six of the best:  ".....that will teach you not to alter the ignorance of a lifetime!"

Newport rockfall removal

In November 2019 I reported on a massive fresh rockfall in the cliffs at the northern end of Traeth Mawr, Newport.   I went back there the other day while we were out for a walk on the beach, and it has almost all gone!   That must all be the result of wave action around HWM -- quite impressive, given that it has not been a particularly stormy winter.  Seven months of wave action, and virtually all of the finer material is gone -- and the larger boulders too have been rearranged and dispersed......

On the new photo below, I have marked in the approx shape of the debris cone as it was when fresh.

Addendum:  19 September 2020.  This is the rockfall site today (a clearer photo).  The remaining debris on the beach seems to have found some sort of equilibrium.....

Sagan, Scrutiny and Baloney

Carl Sagan,  defender of critical thinking

I sometimes get a hard time on certain Facebook group pages because I refuse to believe what senior archaeologists like Parker Pearson, Gaffney or Darvill  tell me -- or tell us, corporately -- in their "learned" articles.  "How dare I criticise them?" they protest. "They are archaeologists who know what they are talking about, and you are novice who knows nothing about their specialisms....."  I try to tell them that it matters not a jot who they are or how famous they may be, or whether I know a lot or a little about archaeology.  The article is the thing.  If it's rubbish, it's rubbish, and if that is not pointed out, then the rubbish is perpetrated and magnified and accepted as "the truth."

I had forgotten how wise Carl Sagan was on the subject of bad research and unsound conclusions.  I came across this video:



There is also a web article, here:

http://www.openculture.com/2018/03/carl-sagans-baloney-detection-kit.html?fbclid=IwAR2oFyiZwA1vOAsUh6XLVqpIxG_r5nEwSEAa_aRNM6xzmJS9Zuf99pHOyes


Extract:

In the essay, a chapter from his 1995 book The Demon-Haunted World, Sagan proposes a rigorous but comprehensible “baloney detection kit” to separate sense from nonsense.

** Wherever possible there must be independent confirmation of the “facts.”

** Encourage substantive debate on the evidence by knowledgeable proponents of all points of view.

** Arguments from authority carry little weight — “authorities” have made mistakes in the past. They will do so again in the future. Perhaps a better way to say it is that in science there are no authorities; at most, there are experts.

** Spin more than one hypothesis. If there’s something to be explained, think of all the different ways in which it could be explained. Then think of tests by which you might systematically disprove each of the alternatives.

** Try not to get overly attached to a hypothesis just because it’s yours. It’s only a way station in the pursuit of knowledge. Ask yourself why you like the idea. Compare it fairly with the alternatives. See if you can find reasons for rejecting it. If you don’t, others will.

** If whatever it is you’re explaining has some measure, some numerical quantity attached to it, you’ll be much better able to discriminate among competing hypotheses. What is vague and qualitative is open to many explanations.

** If there’s a chain of argument, every link in the chain must work (including the premise) — not just most of them.

** Occam’s Razor. This convenient rule-of-thumb urges us when faced with two hypotheses that explain the data equally well to choose the simpler. Always ask whether the hypothesis can be, at least in principle, falsified…. You must be able to check assertions out. Inveterate skeptics must be given the chance to follow your reasoning, to duplicate your experiments and see if they get the same result.

Calling his recommendations “tools for skeptical thinking,” he lays out a means of compensating for the strong emotional pulls that “promise something like old-time religion" and recognizing "a fallacious or fraudulent argument.” At the top of the post, in a video produced by Big Think, you can hear science writer and educator Michael Shermer explain the “baloney detection kit” that he himself adapted from Sagan, and just above, read Sagan’s own version, abridged into a short list (read it in full at Brain Pickings).

Like many a science communicator after him, Sagan was very much concerned with the influence of superstitious religious beliefs. He also foresaw a time in the near future much like our own. Elsewhere in The Demon-Haunted World, Sagan writes of “America in my children’s or grandchildren’s time…. when awesome technological powers are in the hands of a very few.” The loss of control over media and education renders people “unable to distinguish between what feels good and what’s true.”

This state involves, he says a “slide… back into superstition” of the religious variety and also a general "celebration of ignorance," such that well-supported scientific theories carry the same weight or less than explanations made up on the spot by authorities whom people have lost the ability to “knowledgeably question.” It’s a scary scenario that may not have completely come to pass... just yet, but Sagan knew as well or better than anyone of his time how to address such a potential social epidemic.

=================

In my mind, this chimes in perfectly with the points made by Barclay and Brophy about archaeology, research and "interpretative inflation"........  For superstition, read "British Neolithic Mythos".

PS.      I like the reference to people who "have lost the ability to knowledgeably question" the so-called authorities who tell them things or sell them ideas.  That is indeed a social epidemic, and a very dangerous one.  I see the results almost every day, on blogs and in Facebook groups which I follow intermittently -- whenever a spectacular headline appears in the press following a press release relating to Stonehenge, we see a flood of comments showing that people are completely fooled by the snake oil salesmen, with hardly anybody going back to the recently published article itself and subjecting it to critical scrutiny.  Why don't they do that?  The reasons are many and varied -- but it's clear that people are intimidated by articles that have graphs and tables in them and by writing that is often far more complex than it needs to be.  And yes, one has to conclude that most members of the public no longer have the instinct or the ability to examine a text and work out for themeselves that what they are reading is complete tosh.

Clatford Bottom and the sarsens

The widely-favoured theory of sarsen stone formation, by Goudie and others.  This is 

the "periglacial" theory involving the downslope migration of blocks of silcrete.  

The arrow with the words "the ice melts" should really have been labelled "the ground 

ice melts."  Or should it.....??

This is an interesting article from Peter Worsley of Reading University.  Peter and I were contemporaries and met frequently back in the 1960s and 1970s at geomorphology conferences and other events.  I have great respect for his careful work, and it's good to see an article about sarsen sones which is free of wild speculations and assumptions.......

Here is the link:
https://www.researchgate.net/profile/P_Worsley/publication/336003003_Geology_of_the_Clatford_Bottom_catchment_and_its_sarsen_stones_on_the_Marlborough_Downs

Geology of the Clatford Bottom catchment and its sarsen stones on the Marlborough Downs

Peter Worsley
MERCIAN GEOLOGIST 2019 19 (4).p 242-252

Abstract:
The now vanished Palaeogene geology of the Marlborough Downs area can be plausibly reconstructed by extrapolation from the surviving rock record lying immediately to the east. The Lambeth Group succession dominated by the Reading Formation, formerly extended westwards over the Downs. Anastomosing river channels draining from NW to SE created linear belts of sand extending across a clay-rich floodplain and coastal plain. During the Palaeogene/Eocene Thermal Maximum (PETM) global warming event (c.55.5 Ma), groundwater silicification within the sand bodies led to concretion formation (sarsens). Denudational processes led to the sarsens and their Reading Formation host being incorporated into a complex residual deposit, the Clay-with- flints, over Chalk Group bedrock. Following dissection, the Clay-with- flints now occupies the higher chalk interfluves and spurs. During progressive late Cenozoicerosion over at least the last 3 Ma, the present-day relief and its dry valley systems developed under a fluctuating temperate/cold climatic regime. The dominant processes were dissolution of the chalk (this continues today) and fluvial incision, mainly during phases of permafrost development. Following exhumation, the sarsens were lowered as the chalk landscape evolved and later redistributed by solifluction process during repeated cold climate stages.

Most of the article is taken up with a discussion on the origins of the sarsens and the Sarsen stone concentrations of stone streams on valley bottoms -- worth reading since it is clear and concise, with good illustrations.  On the geomorphological context, there are two theories, one involving the breakup of the silcrete crust or cap, the formation of chalk dry valleys and the downslope movement of silcrete slabs and fragments under Ice Age (periglacial) conditions; and the other involving the creation of different types of sarsens depending on environmental conditions at the time of formation, with later resultant slabs and blocks being "let down" onto the landscape without much lateral movement or "migration."  This latter theory seems sensible to me,  since there is no particular reason why sarsen blocks should originally have been more abundant on interfluves.  Indeed, as Worsley explains, the "drainage line" theory might be more attractive since it might account for thicker silcrete crusts on drainage lines or in river valleys, and thinner silcretes on the interfluves -- so although the silcrete blocks might have been let down onto the current landscape by 100m or more, the lateral distribution of silcrete remnants (ie sarsen stones) might not have changed much over 50 million years or so.  

Worsley seems to prefer a composite theory, involving some lateral downslope migration especially at times of cold climate, since he argues that there is no reason to assume that the drainage pattern 55 million years ago looked anything like that of today.  I would argue that it might well have done, since structural lineations, fault lines, etc will have exerted an influence then as now.

Worsley has not got much time for the standard conviction, in archaeological circles, that the Marlborough Downs provided the "quarrying" or extraction locations for all of the big sarsens used at Stonehenge.  He concludes:  " Geological evidence in confirmation of this haulage hypothesis is conspicuous by its absence (John, 2018), although in 2019 the Natural England web site for Fyfield Down has no doubts! A pioneering heavy-mineral study (Howard, 1982) concluded that the Stonehenge sarsen materials differed from sarsen samples from the Marlborough Downs, namely Clatford Bottom and Piggledene. This conclusion has been supported by recent laser scanning data from Stonehenge, which indicate differing chemistries that in turn are likely to reflect source variability. Currently, a project by Nash and Ciborowski at the University of Brighton, using ICP-MS/AES (inductively coupled plasma: mass or atomic emission spectroscopy) analyses seeks to establish geochemical fingerprints of sarsens both at Stonehenge and at potential sources in southern England (including the Marlborough Downs). The jury is still out."

Definitions:

Silcrete:  A terrestrial, geochemical sediment that is formed by low-temperature, near-surface, physico-chemicalprocesses operating within the zone of weathering, in which silica has accumulated in, and/or replaced, a pre-existing soil, sediment, rock or weathering material. Silcretes contain more than 85% silica by weight, with some pure examples consisting of more than 95% silica (Sommer eld, 1983). The term was first introduced by Lamplugh (1902) to describe (in an Irish context) “sporadic masses of ‘grey wether’ type, indurated by a siliceous cement”. (Fr. silcrete)

Clay-with- flints Formation: A residual deposit formed from the dissolution, decalicification and cryoturbation of bedrock strata of the Chalk Group and Palaeogene formations. It is unbedded and heterogeneous, dominated by orange- brown and red-brown sandy clay with abundant nodules and rounded pebbles of flint. Locally it includes bodies of fine to medium grained sand, clayey silt, sandy clay, with beds of well-rounded pebbles and sarsen stones (modified from the BGS online Lexicon). (Fr. Argiles à silex)

Head:  Head is a uniquely British term (some call it archaic as is Drift!), for describing non-sorted and poorly stratified debris mantling hillslopes and partially infilling valley floors. It is the result of solifluction, the slow downslope flow of saturated unfrozen sediments over either dissipating seasonal frost or where the substrate is permafrost, the flow occurs within a thickening active layer. A synonym is gelifluctate. (Fr. depots de couverture) (Comment BSJ: Nowadays this material is generally referred to as slope breccia, stratified, unstratified or pseudo-stratified.)

Coombe deposits:  Compact gravel containing flints and clasts of chalk in a matrix of weathered finely divided chalk-rich and silty material. Frequently found beneath the floors of southern English chalkland dry valleys and where such valleys cut open onto low ground, they form low angle alluvial fans. They reflect a combination of solifluction and fluvial transport, the latter being meltwater deposits derived from either ground ice or snow. Can be crudely mixed or roughly stratified. (Fr. glisements de coombe)

There are interesting discussions relating to the origins of clay-with-flints and head in the Clatford Bottom area, and what impresses me is the sheer lithological variety encountered in exposures.  It is clearly difficult in many locations to decide what label to give to a particular deposit -- and within the "clay-with-flints" category there are brickearths, clay deposits, sandy and gravelly layers and deposits that are really rather similar to tills.  Geoffrey Kellaway made the mistake in 1977 of trying to label ALL of the clay-with-flints as remnants of the Plateau Drift, referring to them as the decalcified remains of a cover of glacial till.  He later revised this opinion, in 1991, but I still wonder whether there has been a very complacent labelling of the "clay-with-flints" as a low-lying blanket of weathered residues derived from overlying beds that have been eroded away over many millions of years.   I would not be at all surprised to find that some of the deposits lumped together under this one label prove to be very old true tills, the last remains of a patchy deposit now largely destroyed.   Has anybody seriously looked for erratics in the deposit?  There would not be many of them, since in tills we find that more than 90% of the stone content can be locally derived -- but the shapes and surface characteristics of many of the Stonehenge bluestones suggest that they are erratics, and they must have been collected from somewhere not too far away.......

 

Exposure of clay-with-flints.  The appearance is not a million miles away from that of a true glacial till.......

Black dots:  locations of silcretes or sarsen stones across southern England.  Many of them are NOT located on the chalklands.... (from a talk by Katy Whitaker).

Bluestones and Interpretative Inflation

Waun Mawn and Craig Rhosyfelein -- two sites where mythification and interpretative inflation have been unrestrained.  The former is promoted as the site of "proto-Stonehenge" and the latter as the site of  a bluestone quarry and "a prehistoric Pompeii".......

It's interesting to reflect further on the significance of the recent article by Gordon Barclay and Kenneth Brophy, not just because of the manner in which Neolithic archaeology in the UK has become dominated by the "British Neolithic Mythos" or mythical narrative, but also because of the diminished respect for evidence and the truth that we see in many so-called "academic" or "scholarly" publications.  At the same time we see the decline of the scientific method, ubiquitous assumptive research, the assignment of false significance, the refusal to set up control studies, and the obsessive use of ruling hypotheses leading to the twisting and manipulation (and also the invention) of evidence.  Some studies have become so distorted that they should probably be classified as scientific hoaxes. 

So scientific malpractice is more and more common.  And it can be no coincidence that this trend has become noticeable while phenomenology has become popular in academic archaeology -- the invention of "the story" is the thing, and facts and evidence are deemed to be rather boring..........  So the truth ceases to matter very much, if at all.

In a world dominated by phenomenology and narrative creation, interpretative inflation becomes inevitable. The four stages of interpretative inflation, according to Barclay and Brophy:

1.  presentation of data with relatively restrained preliminary interpretation in the first part of the original academic paper;

2.  less tentatively, in the later part of the paper (and in the Abstract) more far- reaching interpretation, with less support offered;

3.  even more ambitious claims in media releases prepared by the universities, incorporating direct quotations from the authors;

4.  creation of attention-grabbing headlines and soundbites in the media by journalists working from the press releases,  further amplified through interviews with the lead authors, and affected by the media outlet’s own political angle.

(I might add a phase 2 (b), in which authors of original "learned" papers follow them up with unreferenced and "sexed up" versions of their research in popular glossy archaeology or history magazines.)

We can see this process of inflation at work in almost all of the bluestone-related papers published in recent years by the Bevins / Ixer / Parker Pearson cooperative,  as I have pointed out over and again in my analyses of their work.  We can see it most recently in the many articles cited by Barclay and Brophy relating to Stonehenge, Durrington Walls, teeth, bones and isotopes. (Again, purely by chance, Prof MPP is often involved......)  And we can see it with startling clarity in the recent paper by Vince Gaffney and others on the "Durrington Shafts" which will no doubt have the same fate as the spectacular "line of massive standing stones" supposedly discovered a few years ago. 

Should we be worried?  Well, yes we should -- because when academic standards are lowered and when all that matters is "impact" public cynicism about academia is bound to increase.

So when Sue Greaney give a podcast incorporating a fantastical narrative (and almost a liturgy) relating to a Neolithic burial ceremony, at one level it's a bit of radio entertainment, but at another level it's a demonstration that storytelling and marketing have become more "respectable" than scientific evidence and the truth.

Some years ago I had a bit of a spat with  Bronwen Price about her fantastical interpretation of the Craig Rhosyfelin site on a popular Welsh tourism website called "Land of Legends".  On the site, many fascinating locations were included because of their mythological / literary associations.  The Craig Rhos-y-felin entry should not have been included at all, since there is no mythology attached to the site. (Or at least there wasn't until MPP started to create it.)  But for better or for worse, there it is, written by Bronwen Price of Literature Wales, who has an archaeology doctorate and who should therefore know what she is talking about.  But in almost every respect, this entry is at fault, portraying the assumptions and speculations of a few archaeologists as established fact.  

http://www.landoflegends.wales/theme/sacred-and-spiritual

With regard to the “site description”, these are some of the fundamental errors:

Some of the bluestones of Stonehenge were quarried here. There is no evidence to support this statement. Some small fragments of foliated rhyolite found in the soil at Stonehenge appear to have come from the Rhosyfelin area — that’s the best that can be said. They might have come from destroyed cutting or slicing tools. The use of the word “quarried” is entirely inappropriate.

First used for a local monument in about 3400 BC, they were moved to Salisbury Plain 500 years later where they stood in various settings before the giant inverted ‘U-shaped’ stones joined them in 2500 BC. There is no evidence for there ever being a “local monument” or photo-Stonehenge in the local area around 3400 BC or at any other date. That is a piece of unsupported speculation from Mike Parker-Pearson. There is no evidence that the stones were moved to Salisbury Plain by human agency c 2900 BC or at any other time. The smaller bluestones at Stonehenge were indeed moved about and used in various settings, but there is no proof that the sarsens were not used on the site until later. The expression “giant inverted U-shaped stones” is really rather strange — each of the trilithons consists of two uprights and a capstone.

This makes Stonehenge a truly Welsh site….. This is nonsense.

…..something supported by the Boscombe Bowmen: seven individuals re-buried in a mass grave near Stonehenge around 2300 BC. All were seemingly born and raised in south-west Wales, travelling to Wessex during their lifetime. This is wild speculation — I know of no evidence linking the Boscombe Bowmen to SW Wales. According to all the published analytical data, they are just as likely to have come from elsewhere in South Wales, Devon, Cornwall, or the Lake District or any other area of ancient rocks.

This connection and journeys from the west are recalled in folk legend - Geoffrey of Monmouth (c. 1100-1155) retells the ancient belief that Merlin brought Stonehenge from Ireland. The idea that Geoffrey of Monmouth was repeating some ancient “folk memory” has been around for a long time! But we now know that he invented many of his stories with political and PR considerations in mind — and he was indeed in the business of promoting Wales and its heroes. He was a fiction writer, and not an historian, and he invented the “ancient belief” himself.

The rock face retains the natural pillar formations which the stone-cutters exploited. This is incorrect. On the rock face there are many intersecting fractures, which explains why the most predominant shapes in the slope accumulations are slabs and blocks rather than elongated pillars. There were no “stone-cutters” at Rhosyfelin, in spite of what Mike Parker-Pearson may tell you. In the Neolithic there was no method which allowed the cutting of stone.

You can enjoy a picnic where they camped 5400 years ago. This at least is partly true! Radiocarbon dates show that there is a long history of intermittent occupation by hunting and gathering parties at Rhosyfelin, between the Mesolithic and the Middle Ages. None of the dates coincides with a supposed "quarrying phase". 

When all of this was pointed out to Bronwen Price and Literature Wales, they refused point blank to re-write this entry to more accurately represent the scientific consensus.  Stubborn mules and ostriches with heads in sand come to mind. 

 Neither Visit Wales nor Literature Wales should be in the business of inventing an "alternative truth" or promoting new myths based on dodgy science.  Nor should the archaeology departments of our universities, or the professional academies which supposedly exist to uphold standards.

PS

I have been involved in a jolly spat on a Facebook group page, in which I pointed out that certain contributors who were regurgitating the media praise for the latest Altar Stone paper should really read the paper rather than Daily Mail and Times headlines.  I said that what we were seeing, in the media coverage of that paper, was classic interpretative inflation, since the paper was actually a geology paper with no archaeology in it whatsoever.  Some of the comments were classic ones, submitted by people who were furious that I should seek to undermine the ignorance of a lifetime; they feel, as do many other gullible people, that what eminent archaeology professors say is bound to be correct.  All good fun, but the most interesting thing was that somebody mistakenly used the term "interpretative INFLAMMATION."  I really like that.  Inflammation, of course, means setting something on fire, or in a medical context a bodily reaction to harmful stimuli.  Spot on!