Feedback mechanisms and ice sheet behaviour

Two glacial episodes in Scandinavia -- but why was one more extensive than the other?

This is a very interesting paper on the behaviour of the Scandinavian Ice Sheet. For some time I have been interested in the manner in which feedback mechanisms operate within and on the edges of large ice masses. As readers of this blog will know, I have pondered occasionally on the role played by large troughs (such as Sognefjord in Norway and Nordvestfjord in East Greenland) in the efficient evacuation of ice and the dynamics of the ice mass. Assuming that in each successive glacial cycle these troughs are widened and especially deepened, we can also assume that the efficiency of ice transfer is improved -- but does that mean that ice sheets will get bigger and bigger in each successive glaciation? Not necessarily -- there might be ice edge advances at the trough outlets, but maybe ice edge retreat elsewhere because of ice capture in the trough catchments. In other words, there might be increased ice edge crenellation. This could all get very confusing -- and to their credit Henry Patten and others have already been thinking along these lines with respect to the BIIS.

The authors of the new Scandinavian paper concentrate on the role of gradual sediment filling of the low points in the landscape and the "capturing" of ice flow by spectacular features like the Norwegian Trough. With respect to the BIIS and the Celtic Sea arena, the BRITICE team have already been speculating on whether the Late Devensian Glaciation was the most extensive of all the Quaternary glaciations, partly because of the vast thickness of sea floor sediments across which the ice was flowing -- increased bed lubrication, sediment deformation, accelerated flow rates and a lower surface gradient are all interconnected.  Surging behaviour also comes to mind.  But what are the side effects of the "purges" that seem to have occurred in the Celtic Sea area?  Does a more extensive LGM mean that the glaciation was also more intensive?  Not necessarily.

Interesting questions so far, and not many answers......

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Gustav Jungdal-Olesen, Jane Lund Andersen, Andreas Born, and Vivi Kathrine Pedersen, 2024.
The influence of glacial landscape evolution on Scandinavian ice-sheet dynamics and dimensions
The Cryosphere, 18, 1517–1532, 2024

https://doi.org/10.5194/tc-18-1517-2024

Abstract. 
The Scandinavian topography and bathymetry have been shaped by ice through numerous glacial cycles in the Quaternary. In this study, we investigate how the changing morphology has influenced the Scandinavian ice sheet (SIS) in return. We use a higher-order ice-sheet model to simulate the SIS through a glacial period on three different topographies, representing different stages of glacial landscape evolution in the Quaternary. By forcing the three experiments with the same climate conditions, we isolate the effects of a changing landscape morphology on the evolution and dynamics of the ice sheet. We find that early Quaternary glaciations in Scandinavia were limited in extent and volume by the pre-glacial bathymetry until glacial deposits filled depressions in the North Sea and built out the Norwegian shelf. From middle–late Quaternary (   0:5 Ma) the bathymetry was sufficiently filled to allow for a faster southward expansion of the ice sheet causing a relative increase in ice-sheet volume and extent. Furthermore, we show that the formation of The Norwegian Channel during recent glacial periods restricted southward ice-sheet expansion, only allowing for the ice sheet to advance into the southern North Sea close to glacial maxima. Finally, our experiments indicate that different stretches of The Norwegian Channel may have formed in distinct stages during glacial periods since 0:5 Ma. These results highlight the importance of accounting for changes in landscape morphology through time when inferring ice-sheet history from ice-volume proxies and when interpreting climate variability from past ice-sheet extents.

The extraordinary Mr Croll -- the world's first glaciologist

 

James Croll, looking somewhat unhappy.  He didn't like fieldwork very much -- maybe he had just got wet out on the Scottish moors........

James Croll (1821-1890) was an extraordinary man with very little formal education who became a janitor at the museum of the Andersonian University in Glasgow in 1859 and who taught himself (because of his insatiable appetite for learning and his open access to the university library) physics, astronomy and geology.  He corresponded with Charles Lyell and disagreed with him about the origins of what were then called "drift" deposits, but he was greatly encouraged in his researches by Sir Archibald Geikie, and then obtained a position in the office of the Geological Survey of Scotland.

He is revered in Scotland as one of the country's great scientists and as one of the most original of thinkers, and he stood out from the other "glacialists" of the time, who were mostly geologists who happened to be interested ion the Ice Age. I think we should give him the accolade of being the first genuine glaciologist, because of the manner in which he combined the principles of physics, astronomy, climatology and geology in order to understand how glaciers work and how Ice Ages come and go through geological time. 

He saw the Earth as a single system within which events in one sphere (for example, changes in ocean circulation) had repercussions of knock-on effects in all other spheres. He built on the early work of Agassiz in 1840 to argue strongly against Lyell's "great flood" and for extensive landscape modification by expanded land ice. He developed an astronomical theory of oscillatory climate change 60 years before Milankovitch published a very similar theory. He developed a coherent theory of ice sheet growth and shrinkage, and (without any field measurements to work on) developed the idea of an equilibrium profile. He referred quite clearly to feedback mechanisms in glacier behaviour, and wrote about albedo effects. He considered the effects of ice sheet growth and shrinkage on global sea-level, and proposed considerable eustatic drops of sea-level coinciding with glacial maxima during the Ice age. He even started to explore the idea of isostatic loading and unloading, arising from his observations on Scottish raised beaches. He used bore hole records and used field observations on glacial stratigraphy to illustrate his ideas on glacier oscillations and glacial and interglacial episodes. Most extraordinary of all, he created a "model" of the Antarctic Ice Sheet even though, at that time, nobody had set foot on the Antarctic continent, let alone done any measurements on ice thickness, surface gradients and extent. His "model" incorporated innumerable parameters, most of which are still used in computer-based models today. What might he have achieved had there been computers in his day? Then, from his predictions on the nature of the Antarctic Ice Sheet, he had the temerity to use his "model" to suggest what the Great British Ice Sheet might have looked like at the time of maximum glaciation.......... his map was almost a century ahead of its time, and is reminiscent of the maps still in use around 1960, when I was a student.

He was, of course, in 1879  too radical and too far ahead of everybody else to have escaped unscathed -- and towards the end of his life there was a backlash from the more conservative members of the scientific establishment.  In spite of the fact that he was supported and encouraged by the Geikie brothers, and in spite of his copious and creative correspondence with all the great scientists of his day, he never was a full member of the science elite in Britain, and he was known in some quarters as a "controversialist".  The main criticism directed towards him was that his ideas were unsupported by hard evidence and that he strayed too far into the realm of theory  or speculation.  That was all very sad, because one by one his ideas have been accepted and moved into the mainstream -- and field evidence has supported most of his inspired speculations.  Yes, he made mistakes, but that is what happens on the frontiers of science, and the word "extraordinary" is one that will continue to be used for James Croll by those who examine the origins of the science of glaciology.

https://onlinelibrary.wiley.com/doi/full/10.1002/jqs.3420

‘The most remarkable man’: James Croll, Quaternary scientist
Kevin J. Edwards

Jnl of Quaternary Science
First published: 04 April 2022
https://doi.org/10.1002/jqs.3420

This is the abstract from Kevin Edwards's paper about this "most remarkable man":

ABSTRACT

The year 2021 marked the bicentenary of the birth of James Croll (1821–1890), the self-educated son of a crofter-stonemason, whose life was characterised by a dizzying range of occupations and homes, poor health and financial concerns, and yet he became a pioneer of orbital dynamics and ice age climate change with an impressive record of publication. Drawing upon archival information and recently published observations, this paper explores selected aspects of Croll's biography, his scientific connections and controversies, and that area of his life relevant to Quaternary science. He was a 19th century polymath whose multifaceted contributions have been a catalyst for subsequent systems-based climate science on the grand scale, including the foundations for the seminal work of Milutin Milankovitch on the rhythms of Quaternary environmental change.

See also:

Rose J. 2021. Lyell, the Geikies and Croll's observations on terrestrial glacial sediments and landforms. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 112: 261–274.

Sugden DE. 2014. James Croll (1821–1890): ice, ice ages and the Antarctic connection. Antarctic Science 26: 604–613.

Croll, J. 1879. On the thickness of the Antarctic ice, and its relations to that of the glacial epoch. Quarterly Journal of Science, January, 34 pp.

This is James Croll's map (1879), incorporating many components since proved to be correct. Compare with the more modern maps below. Croll was sure that the Scandinavian and British - Irish ice sheets were connected in the North Sea. Flowlines across Northern Scotland were largely correct. The Irish Sea ice stream is shown quite clearly. The ice edge is correctly located on the Celtic Shelf edge. However, Croll assumed that glaciers had a constant surface gradient from centre to periphery; the glacial equilibrium profile had not yet been discovered. So he greatly overestimated ice thickness in the centre of the accumulation area. Consequently, his image showing thick glacier ice flowing across southern England was somewhat overenthusiastic!! He has ice flowing down the Bristol Channel from east to west -- precisely the opposite of the ice flow pattern as understood today.

The most recent ice flow maps, mostly computer generated, are more correct that Croll's map -- but they are still faulty in some areas because of modelling mistakes and inadequate ground truthing.

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Also found on the web:
Achievements and Key Points

James Croll:

Was the foremost advocate in the 1800s of the idea that climate change is caused by the changing relationship between the earth and the sun.
Devised they theory that climate is controlled by solar insolation – the amount of energy reaching the earth from the sun.
Linked our planet’s ice ages to solar insolation variations caused by: Earth’s elliptical orbit around the sun (100,000-year cycle); precession of the equinoxes (23,000-year cycle); and axial tilt (41,000-year cycle).
Noted how the elliptical shape of Earth’s orbit around the sun varies with time – sometimes the ellipse is more eccentric (elongated).
Said ice ages happen when there is a combination of events: the earth’s elliptical orbit around the sun is at its most eccentric and mid-winter takes place when the earth’s orbit is at its farthest point from the sun. These conditions of reduced sunlight result in lower temperatures, leading to a build-up of ice and snow in the oceans and on the ground.
Said the build-up of ice redirects the trade winds and hence ocean currents. Warm currents like the Gulf Stream no longer bring heat from the tropics to the colder regions, enhancing the orbital cooling effect, leading to ice ages.
Advanced the theory of ice-albedo feedback. This says that if ice begins accumulating at a pole because of a decrease in winter sunlight, then the extra ice will reflect more of the sun’s heat back into space, leading to further cooling.
He (incorrectly) said ice ages alternate between the northern and southern hemispheres – the north and south taking it in turns to have moderate climates and ice climates in a cycle lasting 22,000 years in each hemisphere, with each ice age lasting about 10,000 years.
Although today we know Croll did not get all the details correct, his work provided a mechanism that explained the ice ages. It provided a basis for Milutin Milanković to go further the following century and generate the concept of Milankovitch cycles.

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This is an interesting programme from 2010, in which Iain Stewart talks at some length about the life and times of James Croll -- starting about 30 mins into the programme.

https://www.youtube.com/watch?v=vGnBz0VwXoE

Bluestone transport: Edgar Barclay was the originator of the human transport hypothesis -- not HH Thomas

Two of Barclay's Stonehenge paintings

Reference: 
Barclay, 1895. “Stonehenge and its Earth-works”. Nutt, London, 225 pp.

https://archive.org/details/stonehengeandit00barcgoog/page/n64/mode/2up?view=theater

https://www.sarsen.org/2014/05/barclay-edgar-stonehenge-and-its-earth.html

Thanks to Tim Daw for flagging up this little volume a few years ago. I have been looking at it again,  and while a lot of the contents of the book are naive and fanciful, it contains many astute observations and deductions. Barclay clearly had no contact with the "glacialists" of his day, and he makes no mention in his book of the possibility of glacial stone transport.  He was certainly not the first writer to refer to the "prodigious effort" involved in assembling the Stonehenge monoliths and the building of the monument, but (and here I stand to be corrected) he seems to have been the first person to propose the long-distance transport of the bluestones from their places of origin across the sea and overland. (We can safely ignore Merlin the Wizard and Geoffrey of Monmouth for the time being.....)

He was advised (somewhat prematurely) by the geologists of the day that the bluestones cannot have come from any British rock outcrops, and so he speculated that they might have come from Brittany, and that they were transported across the Channel by our ancient ancestors. He also suggests in his text that the bluestones must have been deemed as special or valuable -- in order to justify the "prodigious effort" involved in moving them. Barclay was also aware the the chippings and bluestone fragments scattered about across the Stonehenge landscape, and of a link with the abundant round barrows on the chalk downs.

I think the key passages in the text below justifies us in giving the credit -- or the blame --to Barclay for the invention of the human transport hypothesis in 1895.  What HHT did 28 years later was to correct the source area to West Wales and to add the petrological detail which permitted him to claim (again somewhat prematurely) that he knew pretty well exactly where the bluestones had come from. In 1858 Ramsey had suggested that Wales was the source for the bluestones.   It's worth remembering that neither Barclay nor Thomas believed that the bluestones had been quarried.  Both of them realised that the bluestones were simply weathered boulders collected up from what had been a scatter across the landscape.

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Edgar Barclay (1842-1913)

The artist Edgar Barclay was born in 1842 and studied art in Italy and Germany. For several years as a working artist he divided his time between London and Italy, but he returned to England in the 1880s and began painting rural scenes of Wessex, especially of Stonehenge. He exhibited extensively and was known for his skill in handling light and big skies. He was also an accomplished historian, writing and speaking particularly on Stonehenge. He addressed the British Archaeological Association in 1893. He clearly had good contacts, and wrote "Stonehenge and Its Earth-Works” in 1895. He suggested -- because of the weathering crusts on many of the bluestones -- that they were simply collected as boulders rather than being quarried.

Extracts:

p 6
The inner circle and inner horse-shoe are composed of the foreign  "Blue-stones",  igneous rocks. The locality from which they were originally taken remains undetermined ; experts, after microscopic examination, have affirmed that in "no part of Great Britain is there any stone to be found of the same description." Of these some differ markedly in their nature from others.

p 77
The most arduous operation in connection with the erection of Stonehenge was the transportation of the Blue-stones ; we should, therefore, be forced to believe that although the builders lacked the energy to complete a gap in the Sarsen circle, they nevertheless had the opportunity and energy to fetch and set up the Bluestones. This is a contradiction ; we therefore conclude that stones are missing because the building has suffered from spoliation. Fortunately, ancient records which make mention of Stonehenge inform us how this probably came to pass.

pp 124-126
In conclusion, we take a retrospective glance at the results of our inquiry. To begin, there is the striking fact that Stonehenge consists of stones foreign to the neighbourhood, and belonging to geological formations widely apart ; proof that its construction was a far greater undertaking than the present appearance of the ruin would lead any one to suspect, and of the power of the founders to organize labour on a very considerable scale.

This is specially shown by the case of the Blue-stones, which, according to the judgment of experts, are foreign to this country, and which, so it has been concluded, from the weathered surfaces of some of their chippings, were, like the larger Sarsens, never quarried, but derived from boulders left on the surface, or, more probably, were brought from some sea-washed shore.

The labour of carrying these stones up from the coast was no mean one, and that they should have been transported across the sea is not merely a conspicuous proof of the resources of the founders, but indicates either that those who controlled the work were themselves moved by a strong sentimental motive, or that they played upon a strong sentimental feeling animating others, otherwise so laborious and unusual a course, and one so uncalled for by any utilitarian purpose, would never have been pursued.

The dictum of petrologists, that the Blue-stones are of foreign origin, is in harmony with the tradition that the stones have been transported hither by sea. The geological formation of Brittany points to that country as their probable source, a probability greatly strengthened by historical considerations. Geoffrey of Monmouth, when giving an account of additions effected by King Aurelius to the monastery at Amesbury, followed a tradition which stated that a stone circle was taken down and utilized for that purpose. We have no reason to believe that Geoffrey had knowledge of Stonehenge, situated a mile distant west of the monastery ; and mystified by another tradition which stated that the stones had been shipped, it appears that he in consequence concluded that the stone circle in question must have been situated in Ireland ; thus he kept to the right direction for their source, whilst considerably exceeding the real distance. It is incredible that Aurelius should have brought his building material from that country; he had not the power, supposing he had the crazy desire to do so ; he had no fleet, and the sea was commanded by piratical Saxons, his deadly enemies. In the introduction of the Irish incident we, therefore, recognize Geoffrey's embellishments ; we here see the old familiar artifice of making an incredible story appear veracious, by the introduction of circumstantial details, thus in the thick of the Irish embroglio he makes his characters orate in the time-honoured classical and biblical manner.

The Altar-stone belongs to a different geological formation to either the Wiltshire Sarsens or the foreign stones, and affords another proof of lavish expenditure of labour ; whilst the shaping of the rocks, and the manner in which the superimposed blocks are securely locked in their places by means of tenon and mortise, evidences the attainment of considerable skill.

Moreover, it is a striking fact that these rocks, collected with prodigal labour from sources so widely apart, should have been set up on a bare and desolate down, the surrounding land for the space of several miles being more thickly studded with barrows than any other district in this country, which produces a strong impression, the correctness of which is fully confirmed by closer scrutiny, that the ruin and the gravemounds are in some way connected. We noted the critical positions of the outlying stones, and that mysterious alignments proceed from the ruin and traverse the barrow-studded plain.

The design has manifestly not been dictated by utilitarian necessities, or by aesthetic sentiment, it shows the temple to have been dedicated to Sun-worship, the stones being so disposed as to form religious symbols ; the meaning of that symbolism we have endeavoured to explain, and in doing so we have followed ideas once current in Gaul.

The unity of the design was proved by the relative proportions of the parts, and that the different parts were raised at the same epoch is further attested, first, by the finding together of pieces of the different sorts of stone used in the construction within a gravemound, and, secondly, by chippings of all the rocks having been found in the concreted substance around the bases of the Bluestones. When thus proving the unity of the design, we proved also that the temple is not of prehistoric antiquity, for we have no reason to believe that the ancient Britons were capable of adjusting their buildings with a knowledge of geometry.

What did HH Thomas know about the extent of glaciation?

I have been digging up some more info about what HH Thomas knew or did not know when he presented his controversial views on the transport of the bluestones in 1923.  (And in 1921, actually......)  

Let's take 1910 as a reasonable date to look at.  The "state of play" was determined at the time by such senior geologists and "glacialists" as James Geikie (far more important than his older brother Sir Archibald), Carvill Lewis, Frederick Wright,  Thomas Jehu and John Wesley Judd. 

Henry Carvill Lewis (1853-1888) , an American who did much fieldwork in the British Isles.  He proposed that the edge of the great Ice Age glaciation in Britain  coincided with a line of prominent moraines and other features which could be traces across country.  At first he found it difficult to accept that traces (such as erratic boulders) south of his limit were genuinely related to the presence of glacier ice, and he initially assigned them to some great Ice Age Flood. But later in his all-too-short life he fell into line with Geikie and others and did accept that the maximum position of the ice edge in the Ice Age was well to the south of his hypothetical line. 

 

Prof James Geikie (1839-1915), a Scottish geologist who was convinced that there was very extensive glaciation in the Ice Age, and that the ice limit in SW England lay somewhere off the Cornish coast. he was also active in promoting the idea that there had been several glaciations, separated by warmer intervals or interglacials.

Frederick Wright’s map of 1895, showing a strange ice limit across South Wales, based in part on Carvill Lewis’s identification of assumed terminal moraines. Wright ignored the abundant records of far-travelled erratics to the south of this line.

Europe and the greatest extent of glaciation during the Ice Age. From “Prehistoric Europe - A Geological Sketch”, by James Geikie (Edward Stanford, London, 1881). Note that Geikie incorporates the whole of the Bristol Channel area into the glaciated area, with an ice edge on or near Salisbury Plain……..

In this map, also from Wright (1895) a highly generalised line, based on the work of James Geikie, is drawn well to the south of the “moraines” identified by Carvill Lewis. Geikie recognised that the abundance of glacial erratics around the Bristol Channel coasts indicated extensive glaciation, at least as far south as the Cornish coast.

Extract from Harmer’s “erratic map” of 1928, showing erratic boulders and ”drift” exposures in abundant locations including South Pembrokeshire, Gower, Glamorgan and the Ilfracombe district — all to the south of the “moraines” mapped by Carvill Lewis. The work on this map was done between 1902 and 1913, and it must have been known to HH Thomas.

Prof Thomas Jehu (1871-1943) was born in Wales and later spent most of his working career in Scotland. As a young man he studied the glacial deposits of North Pembrokeshire, and published his findings in a highly regarded article in 1904. He recognized a tripartite succession in the drift sequence of Pembrokeshire -- namely Lower boulder clay, Middle sands and gravels, and Upper boulder-clay.  He characterised the latter deposit as a "rubbly drift" -- this is now recognized as a mixed deposit of melt-out till, flowtill and ablation till, rearranged and redeposited in a chaotic ice wastage environment.  Jehu agreed with Hicks that the Irish Sea ice that affected North Pembrokeshire flowed across the county from NW towards SE -- thus contradicting Geikie who had earlier portrayed the ice as having travelled from NE towards SW,

 Prof John Wesley Judd (1940-1916) was a prominent geologist who specialised in petrology.  He was Professor of Geology in the Royal College of Science and at Imperial College, and also President of the Geological Society.  Because he was London-based, he was right at the centre of things, and knew all about what was going on in assorted disputes and areas of progress.  He participated actively in the Stonehenge bluestone debate, and provided comments or additional material to some of the prominent archaeologists includingGowland and Hawley.  In 1901, Judd suggested that the bluestones at Stonehenge were erratics of glacial origin. He argued that the debris at Stonehenge had come from North Pembrokeshire or North Wales. He also observed that in areas affected by very ancient glaciations, most of the till had been eroded away by natural processes, leaving only a thin scatter of erratics here and there. Further, he observed that hard stones (including bluestones) left behind on Salisbury Plain would have been targetted down through the centuries for building purposes simply because neither chalk nor flint makes good building material.  Intriguingly, Judd concentrated not on the 43 known bluestone monoliths or orthostats themselves, but on the Stonehenge debitage. He found an extraordinary assortment of soft or fragile stones.  He made the point specifically that this material did not seem to be very closely related to the remaining standing bluestones -- so he concluded that only the hardest stones had survived, with all the other material breaking down and becoming incorporated into the soil layer over many thousands of years.  Judd suggested the presence of a “Stonehenge moraine” incorporating an abundance of foreign stones which would have been readily available to the builders of Stonehenge. He also argued -- perfectly plausibly -- that “stone availability” (of both bluestones and the larger sarsens) might have actually determined the precise position of the monument. 

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All things considered, the accumulated evidence shows that by 1910 the broad outlines of glaciation in the Bristol Channel / Celtic Sea arena were already established, involving thick and active ice carrying erratics and other glacial materials from the NW across Pembrokeshire and up the Bristol Channel, affecting the coasts of South Wales and the South-West Peninsula. In making his claims about the impossibility of bluestone transport towards Stonehenge HH Thomas wilfully ignored a great amount of evidence in the printed literature, and wilfully misrepresented the opinions of senior "glacialists". It is quite extraordinary that he got away with it -- but that, maybe, was because he was a geologist talking to archaeologists or antiquarians. If he had been a geologist talking to other geologists, he would certainly not have got away with it.  They would have had his guts for garters. 

Interestingly enough, the great majority of the articles published by Ixer and Bevins in recent years have also been published in archaeological journals -- and presumably they have been refereed for the most part by archaeologists. What a strange coincidence........!!

HH Thomas knowingly misrepresented the glacial erratic transport evidence in the Bristol Channel

I have been looking again at the manner in which, in 1923, HH Thomas informed the world that the glacial transport of bluestones from west to east (up the Bristol Channel) would have been impossible.  Here is an earlier post of mine:

https://brian-mountainman.blogspot.com/2019/10/hh-thomas-and-his-glacial-blind-spot.html

Thomas was guilty of over-simplification and selective citation of his samples (there were very few anyway) and his rock identifications, in order to flag up the idea that there were just two main sources for the bluestones. It's interesting that in 2018 Bevins and Ixer attacked Thomas's slapdash methods, his sharp practices and his reputation pretty enthusiastically, but they restricted their scrutiny to his geological analyses, and criticised him for homing in on Carn Meini and Carn Alw as the main source locations for the Stonehenge bluestones.

https://brian-mountainman.blogspot.com/2018/06/herbert-thomas-scrutinized.html

https://brian-mountainman.blogspot.com/2011/03/more-on-hh-thomas.html

https://brian-mountainman.blogspot.com/2022/06/dale-judd-and-engleheart-versus-thomas.html

Retracing the footsteps of H.H. Thomas: a review of his Stonehenge bluestone provenancing study.
Richard Bevins and Rob Ixer
Antiquity, May 2018.
https://doi.org/10.15184/aqy.2018.10
Published online: 31 May 2018

Bevins and Ixer later (in the magazine called Liver Science) went off on a tangent and tried to demonstrate (without any evidence at at all)  that the bluestones were transported by land instead of by sea.  That was a serious waste of time and effort, especially since HHT did not try to promote the idea of sea transport either.  That came later, with the involvement of Atkinson and other archaeologists.

https://www.livescience.com/63003-sloppy-stonehenge-study.html 

Also, it's rather ironic that in attacking HHT for concentrating on the "wrong" two tors, they then concentrated on trying to convince the rest of us that two other tors or rock outcrops (Carn Goedog and Rhosyfelin) were key to the understanding of what went on  -- while admitting in other papers that the bluestone monoliths and fragments at Stonehenge have come from multiple locations.  Not for the first time, pots and kettles come to mind!

B and I  also declined to comment on the most influential part of the HHT paper -- namely the section dealing with the bluestone "mode of transport."  But the section in the 1923 paper on the "ice transport option" is truly awful, misrepresenting all sorts of things and including many statements that HHT must have known were untrue -- even allowing for the fact that he was writing a century ago. That section should have been scrutinized.   Below I reproduce the key part of the infamous paper, with some comments of my own.

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Extract from HH Thomas, 1923 Antiquaries Journal

MODE OF TRANSPORT

Having in a great measure solved the problem of the source of the Foreign Stones, we must consider carefully the possible and probable modes of transport of the stones from Pembrokeshire to Salisbury Plain. Two modes of transport have been suggested : one natural, by ice during the great Ice Age ; the other, by human agency at, of course, a later period.

The Hypothesis of Ice-transport. 

Professor Judd in 1901 put forward the hypothesis that the Foreign Stones of Stonehenge had been transported to the Plain by ice during the Pleistocene Glacial Period, and this view seems to have found favour and acceptance in many quarters.

We have, of late years, considerably advanced our knowledge of the distribution and extent of the British Ice-fields, and also accumulated much information concerning the directions and limits of dispersal of erratic boulders. The geological evidence is such that the idea of a glacial origin for the Foreign Stones will not bear investigation.

((Comment:  Perhaps not a good idea to get your conclusion in first, before considering the evidence.........))

Let us consider critically this hypothesis of glacial transport as suggested by Professor Judd. First, there is no evidence of glacial drift on Salisbury Plain such as would of necessity have been left by any ice-sheet capable of transporting the masses of rock in question. Isolated masses of rocks foreign to the district, other than those used in the fabric of Stonehenge are entirely wanting, as also are small pebbles of such rocks from the gravels of the neighbourhood. It has been claimed, without producing any evidence in support of the statement, that such masses did exist but that they have all been collected to make walls, gateposts, millstones, etc. But, as Mr. Stevens of Salisbury has cogently stated, no one can point to a single rock-mass like any of those used at Stonehenge having been put to any such purpose. Mr. Stevens says ' There are many millstones and gateposts in Wiltshire, but where is there one which corresponds in any way to the upright Foreign Stones of Stonehenge ? Unhappily this tangible evidence is wanting ; so, alluring as the Glacial Drift Theory may appear, it must reluctantly be set aside for want of convincing evidence.'

((Comment: It's disingenuous of Thomas to pretend that substantial "rock masses" of exactly the right type on Salisbury Plain are required in order to demonstrate that glacial entrainment and transport might have occurred. There are erratic stones in the records of work prior to 1923, and the Boles Barrow bluestone was already on the record following its discovery by Cunnington in 1801.  If you want to wear rose-tinted spectacles rather than dark sunglasses, you might wish to count the Stonehenge bluestone assemblage as quite valid evidence of glacial transport and dumping, and Thomas should have acknowledged this.))

To transport glacially a series of igneous boulders of great size from Pembrokeshire to Wiltshire postulates the existence of an ice-sheet of unbroken character occupying the whole of the intervening country ; and with the ice moving in a direction a little south of east. We have, fortunately, good evidence of the extent of glaciation of Pembrokeshire, and we find that this county was crossed in a south-easterly direction by an ice-sheet that moved down the Irish Sea. This ice-sheet carrying Scottish
boulders, crossed the low plateau of Anglesey and Carnarvon, gathering fresh material as it went, but was kept from passing far inland by the local Welsh ice-sheet that had its centre of dispersal in the highlands of Snowdon, The Arenigs and Cader Idris, and was pressing outwards towards the coast. On reaching the latitude of Pembrokeshire, far removed from the main centre of Welsh glaciation, the Irish Sea ice-sheet was allowed to spread fanwise and to override the plateau-regions of Pembrokeshire and Southern Ireland which offered relatively little opposition. In spite of this there is the clearest evidence, from the distribution of Pembrokeshire and Scottish boulders that the ice-front lay only just south 

of the present coast-line of Pembrokeshire, and that the ice as a solid mass neither crossed the Bristol Channel to Devon and Cornwall, nor passed in an easterly direction beyond the coastal regions of Pembrokeshire. 

((Comment: This is utter nonsense, and Thomas must have known it.  We are talking here of the maximum known glaciation in the region.  To claim that the glacier ice front lay just to the south of the Pembrokeshire coast, and to claim that the ice progressed no further up the Bristol Channel,  is to fly in the face of the evidence that had been in the public domain for more than 20 years.  Jehu and many other professional geologists must have been appalled by Thomas's claims.  Judd, who died in 1916, would have turned in his grave.  Glacial deposits were already known, and described in the literature, from the Bridgend - Pencoed area, from Fremington, Trebetherick and the Isles of Scilly -- all attesting to a very extensive glaciation  that could, even according to the thinking of geologists in 1923, have extended to Somerset and Salisbury Plain. Thomas must have known of the Pentre, Newton and St Athan erratic boulders in the Vale of Glamorgan, all three almost certainly from Pembrokeshire.  And far-travelled glacial erratics were already described from the coasts of Devon and Cornwall.))

No boulders of Pembrokeshire rocks, such as would of necessity be carried by any extension of this icesheet, have ever been found either on the north coast of Devon, Cornwall or Somerset, or on the south coast of Wales east of the estuary of the River Towy.

((Comment:  That is not correct. The Pembrokeshire erratics in the Storrie Collection, from the till at Pencoed in Glamorgan, were well known by 1923. Indeed, Thomas himself was one member of the Geological Survey team that described the erratics in the Bridgend GS Memoir of 1904.))

Scottish boulders, however, occur on the north coast of Devon and on the coast of Glamorganshire where their presence, unmixed with Pembrokeshire boulders, indicates that they were not carried by that portion of the ice-sheet which had crossed Pembrokeshire but had been borne by the portion that came down the central region of the Irish Sea. The ice-sheet would probably have a crescentic front and the medial portion would have the furthest southerly extension. It is to be noticed that all the occurrences of Scottish boulders outside Pembrokeshire and its adjacent islands lie at raised-beach level, as at Croyde Bay and in Glamorganshire. There is no evidence of the erratic material mounting the cliffs or extending inland. The inference is, therefore, that these Scottish boulders were deposited from icebergs that had broken away from the central portion of the main ice-front and were stranded on relatively distant shores. The geological evidence proves conclusively that although Pembrokeshire was crossed in a south-easterly direction by a lobe of the Irish Sea ice-sheet the front of this ice-sheet never reached across or far up the Bristol Channel.

((Comment:  Thomas gets himself into a frightful tangle over the shape, thickness and  movement of  "the ice sheet" -- and although he may be right to assume that Scottish erratic boulders were constrained within a segment of the ice stream, he must have known the evidence on the file that Pembrokeshire erratics were in fact transported much further east than the Towy estuary.))

Passing to the country intervening between Pembrokeshire and Wiltshire, we find nowhere along the line that an ice-sheet would have to traverse in order to transport Pembrokeshire boulders to Salisbury Plain, any evidence of glaciation of an intense character. 

((Comment:  This is a somewhat absurd statement, given that most of this territory is currently under water.  And what sort of glaciation is to be counted as "of an intense character" as distinct from one that is not intense?))

There are no trains of far-travelled boulders, no ice-scratching and polishing of outstanding rocks, and no thick accumulations of boulder-clay. As has been pointed out in a previous communication such a hypothetical ice-sheet, in order to account for the Foreign Stones of Stonehenge would have to gather from Pembrokeshire blocks all of about the same size and mainly of two rock-types. It would have to carry them all that distance without dropping any by the way. 

((Comment:  Here, Thomas raises the nonsensical idea that ice cannot possibly have delivered to Stonehenge exactly the right number of bluestones, of the right colour and lithology, to satisfy the designers and the builders of the monument.  This has, of course, been repeated many times since.  So many unsupported assumptions are built into that it is really not worth wasting time on them.))

Further, it would have to pass over all kinds of rocky obstacles without gathering to itself any of the various materials over which it was forced to ride. Such in itself, without the additional positive evidence that is forthcoming as to the extent of the glaciation of Pembrokeshire and adjoining counties, permanently disposes of the idea of glacial transport for the Foreign Stones of Stonehenge.

((Comment:  Thomas must have known, from his work with the Geological Survey including Cantrill, Strahan, Dixon and Jones, that glacial entrainment, transport and deposition are complex matters which are difficult to predict and which constantly throw up surprises in the field.  The apparent absence of erratics from all upglacier outcrops does not (and did not in 1923) demonstrate the absence of glaciation.))

Note: The rocks of the Western Isles, Ailsa Craig, and Galloway are fairly common as erratics. They occur on the Cardigan coast, on the plateau-region of Pembrokeshire and its outlying islands (Skomer, Skokholm, etc.), and on the Glamorganshire coastal regions of the Bristol Channel.

=========

I'm still staggered that Thomas was allowed to get away with all of this, and to make such definitive statements on the record.  We know that a few people -- including Engleheart and Dale -- were sceptical, but where were all the geologists who knew that he was talking nonsense?  Was he such a forceful character that nobody had the guts to challenge him?  Or was the establishment view already established -- namely that the human transport of the bluestones was a matter of national pride, meaning that anybody who challenged the idea could be charged with being unpatriotic?

The unhealthy obsession with bluestone tors

One of the "high crags" of Preseli -- this one is on Foel Drygarn

As a result of some interesting recent correspondence with a knowledgeable reader of my latest article in "The Holocene",  I have been thinking afresh about the manner in which the bluestone tors of Preseli don't just dominate the upland landscape, but also dominate the debate about Stonehenge.  Ever since 1923, when HH Thomas homed in on the tors of Preseli as the likely sources of most of the bluestone monoliths at Stonehenge,  it has been assumed that the monoliths were taken from the most prominent places in the landscape -- the high crags.  Literally thousands of learned academic papers, book chapters, journal articles, popular magazine features, news reports, TV programmes etc have unknowingly and unthinkingly signed up to the same assumption.  Did the spotted dolerite monoliths (and fragments in the debitage) come from Carn Meini or Carn Goedog, Cerrig Marchogion or Carn Alw, Carn Ddafad-las or Carn Gyfrwy?  Acres of newsprint and millions of words devoted to the question "Here, or there?", "This tor or that tor?"

It's actually quite intriguing.  I have got caught up in it myself, what with my blog posts extolling the virtues of the Preseli and Carningli tors and trying to encourage the general public to visit them and value them:

https://brian-mountainman.blogspot.com/2021/01/the-tors-of-carningli-and-mynydd-dinas.html 

https://brian-mountainman.blogspot.com/2016/12/the-preseli-tors.html

Because they are so beautiful and impressive, it is easy to attach to the tors some sort of spiritual or sacred quality, and to say that "they have always been worshipped" or that they have always been deemed to be associated with the gods. In the Christian era some tors at least must have been invested with significance: Carningli summit was the place where St Brynach "communed with the angels", and the Bronze Age burial mounds on the summit of Foeldrygarn must indicate a reverence for the place............

Then it's very easy to slip into the habit of linking these high rocky places with power or territorial control. The hillforts on Foel Drygarn, Carn Alw, Carningli and Carnffoi must have been built not just because these were good defensive sites but because they were statements of power: this is my territory -- keep away, or stray into it at your peril.......It's not much of a leap from there to assume (as the archaeologists have done) that since Stonehenge was as much a political statement as anything else, its component stones must have been sacred or powerful in themselves, so they must have come from sacred places, so they must have come from "the high places" that dominated the Preseli skyline, so they must have been quarried. We are of course now into circular reasoning, but that hasn't bothered anybody very much.

But hang on. Is there actually any evidence in West Wales that these "high rocky places" were valued by our prehistoric ancestors, and that the stones that came from the tors were especially sacred or special? Interestingly enough, there isn't. Let's look at the big and famous megalithic structures of West Wales. Pentre Ifan cromlech was not made from stones imported from a tor or high point in the landscape; the stones used were taken from a litter of largely local erratics. At Bedd yr Afanc the stones used are of several types, picked up locally and apparently used randomly. Carreg Samson has nothing to do with a prominent rock outcrop, and neither does Gors Fawr, and neither does King's Quoit, Coetan Arthur, Carreg Coetan Arthur, Bedd Arthur, or any of the other stone settings of West Wales. As pointed out by Nora Figgis, Steve Burrow, Stephen Briggs, Olwen Williams-Thorpe, Nikki Cook and many others, the Neolithic and Bronze Age monuments are all built of boulders, pillars and slabs of rock found locally and used more or less where found.  The three Bronze Age burial mounds on Foel Drygarn are made of local bedrock slabs, not because they were sacred but because they were easily collected from adjacent outcrops.

Now let's think about geology. In his original work on the provenancing of the bluestones, HH Thomas was completely dependent for his analysis on samples taken from the crags. He did not do his own sample collecting, but depended upon samples collected by his BGS colleagues around 20 years previously. For practical reasons these came from prominent rock outcrops and not from the intervening saddles, cols and lower parts of the landscape. That, of course, introduced sampling bias. This bias has run through into the abundant studies by Rob Ixer, Richard Bevins and others within the last 15 years. They have studied hundreds of thin sections and collected samples from the high crags, always on the assumption that these are the "candidate" locations from which the bluestone monoliths must have come. They have found no perfect matches with Stonehenge samples, and although their provenancing work must by now have become reasonably accurate, they have had to admit, over and again, that some of their samples just do not quite fit their preferred source locations.   As I have suggested many times on this blog, some of the foliated rhyolite material at Stonehenge might have come from Pont Saeson - Rhosyfelin, from one or more outcrops currently unsampled.  Some of the spotted dolerite boulders and debris at Stonehenge might have come from the Carn Goedog sill, which covers c 60,000 sq m, but not necessarily from the tor itself.

https://brian-mountainman.blogspot.com/2014/09/more-thoughts-on-carn-goedog.html

Carn Goedog, Carn Alw and Carn Breseb -- lots of samples from the tors, but how many from the intervening landscape?

In their most recent "provenancing paper", Bevins et al (2022) demonstrate all too clearly how biased all of their work has been, regarding the attention paid to the "high crags".  In seeking to discover where the unspotted dolerite boulders and fragments at Waun Mawn might have come from, it is clear that their underlying assumption is that the stones must have been fetched from somewhere else. That's dodgy enough as it is, but then the additional assumption is that they must have been fetched from somewhere prominent. All of their "candidate sites" subjected to detailed analysis are high crags or tors -- for example Cerrigmarchogion, Carn Ddu Fach, Carngoedog, and Carn Fach.  They do not provide matches for Waun Mawn, and so further analyses are undertaken on samples from Cerrig Lladron and Carnau Ysfa -- small crags or tors closer to Waun Mawn.  Cerrig Lladron is found to give the best petrological / geochemical match, and so that is proposed as a probable source for the Waun Mawn monoliths.  They claim that these are the closest rock dolerite outcrops to Waun Mawn, but that is incorrect. There are other outcrops of dolerite on Waun Mawn moor itself, adjacent to the site of the supposed "lost giant circle".   The fact that these outcrops were completely ignored in such a detailed study is extraordinary.

Bevins, R.E., Pearce, N.J.G., Parker Pearson, M., Ixer, R.A. 2022. Identification of the source of dolerites used at the Waun Mawn stone circle in the Mynydd Preseli, west Wales and implications for the proposed link with Stonehenge. Journal of Archaeological Science: Reports 45 (2022) 103556.

https://www.researchgate.net/publication/ 362119860_Identification_of_the_source_of_dolerites_used_at_the_Waun_Mawn_stone_circle_in_ the_Mynydd_Preseli_west_Wales_and_implications_for_the_proposed_link_with_Stonehenge

So this question arises: might the bulk of the Stonehenge bluestones have come from unsampled parts of the known and mapped Preseli intrusions and volcanic rock outcrops?

In answer to that question, we can point out that it is no longer tenable to refer to a small number of preferred bluestone locations in which quarrying activity was concentrated. The geologists themselves have had to admit that the sheer abundance of rock types in the Stonehenge bluestone assemblage points to multiple provenances, and that in itself points to glacial, rather than human, bluestone transport.

This brings us to glacial theory. From what we know about glacial entrainment and the transport of "quarried" or plucked blocks under or within an overriding glacier, is it possible that the Stonehenge bluestones have come exclusively from the high crags? From a number of recently published papers, this scenario looks increasingly unlikely. Back in 1965 my old friend Prof David Sugden argued, in his doctorate thesis, that some of the tors in the Cairngorms appear to have been protected, rather than eroded, by overlying ice. A number of subsequent articles, involving many different researchers, have pointed to the survival of tors on high mountain plateaux in other glaciated regions because the thin ice that covered them was cold based and largely immobile. In contrast, erosion was concentrated on the lower slopes and in the troughs where the ice was thicker, warm-based and fast flowing. This means that it was more "aggressive" in landscape transformation.

This suggestion appears to be supported by some of the new work on the cosmogenic exposure ages of rock surfaces in glaciated areas.  To generalise, samples taken on the surfaces of erratic boulders appear, more often than not, to make sense; but samples taken on summit bedrock slabs are throwing up so many anomalies that it must be inferred that the recorded ages are false because of "age inheritance" over maybe hundreds of thousands of years.  This in turn points to very limited or minimal glacial erosion or actual protection on these high rock surfaces.  I will shortly be doing another post on this.  See my comments on Carningli and Lundy Island:

https://brian-mountainman.blogspot.com/2011/03/glaciation-of-carningli-dating-problem.html

https://brian-mountainman.blogspot.com/2014/07/lundy-island-and-lgm-dilemma.html

I have suggested in a number of publications (including my 2018 book called "The Stonehenge Bluestones") that although the high crags of Preseli do show evidence of glacial moulding and abrasion processes, the bulk of erosional activity was concentrated on the up-glacier or northern slope of Preseli, where erosional activity was optimised under streaming or fast-flowing ice where there was melting on the bed. These "erosional hot spots" probably did not coincide with the tors or high crags, but with the intervening areas, valleys (like the Afon Brynberian gorge around Rhosyfelin) or with roche moutonnee features where there were great variations in glacier bed conditions. In Scotland they call these areas "straths" -- but we could call them moorlands (as distinct from the higher plateaux areas).    I will develop this in future posts.

But for now, here is a thought. I THINK THAT ALL OF THE GEOLOGICAL PROVENANCING WORK DONE OVER THE PAST 15 YEARS BY BEVINS, IXER AND THEIR COLLEAGUES MIGHT WELL BE COMPROMISED OR DEVALUED SIMPLY BECAUSE THEY HAVE TAKEN ALL OF THEIR SAMPLES FROM THE WRONG PLACES.

I'm not joking. I say this in all seriousess. Watch this space.

The Lost Circle Fog and the gullibility of the media

 

I have been doing an interesting exercise -- checking back on the gullibility of the media and the coverage of the "Lost Circle" story in February 2021.  You will recall that there was a very carefully orchestrated publicity campaign at the time, with the first transmission of the "Lost Circle" TV documentary timed to coincide with the publication of the original Antiquity article. The amount of work that went into this cannot be overstated -- the documentary maker, the broadcaster, the authors of the journal article, the publishers of "Antiquity", the UCL press office and many others must have been in the loop.   All were intent upon maximum publicity and maximum impact -- and who cares anyway about the reliability of what is being promoted as one of the stories of the century?

https://brian-mountainman.blogspot.com/2021/02/the-original-stonehenge-here-we-go-again.html 

https://brian-mountainman.blogspot.com/2021/02/antiquity-article-on-lost-circle-review.html

https://brian-mountainman.blogspot.com/2021/02/the-mythologisation-of-parker-pearson.html

No wonder, with all that high-powered pressure, that the media fell for it hook, line and sinker. At the head of this post are just a few of the headlines in just a few of the media outlets. There were scores of others in similar vein. The reports were filled with incredulity, certainty and admiration for the exploits and persistence of the research team. Hardly any of the journalists who covered the story expressed any reservations or used the words "possible" or "may".  Most of them simply regurgitated the contents of the UCL press release -- or similar press releases from the press offices of other institutions linked to the research team of about a dozen authors. 

As we knew at the time -- around 3 years ago -- a lot of the contents of the TV documentary and the Antiquity article were poorly researched and deeply misleading. The programme should never have been made and broadcast, and the article should never have been published. I said all that at the time, and I say it again now, following the recent retraction of many of the things that were claimed by the authors themselves. The "complete circle" has gone; the monolith imprint has gone; the geological link with the so-called "quarries" has gone; the monolith export to Stonehenge has gone; and it's now accepted that Waun Mawn had nothing whatsoever to do with Stonehenge.

It's all a bit of a fog, with some reliable information out there somewhere, but almost impossible to discern.......

There are many lessons to be learned -- but will they be learned? I have my doubts. For start, archaeologists (and geologists) should not be so obsessed with IMPACT that they rush into print and present half-baked ideas as realities and inadequate field observations as hard evidence. University press offices should be much more careful about the choice of papers given high-level PR treatment.  Journal editors should be much more careful about their choice of peer reviewers and about their publication decisions.  And the media should be much more circumspect when assessing the press releases coming from certain press offices and when deciding what coverage to give to "spectacular" stories.

Will any those involved in this fiasco regret their errors of judgement, or admit that they have been conned, or apologise to their customers or to those who have grant-aided them?  I doubt it very much.........

And will the media cover the publication of my new paper in The Holocene journal, published after very tight peer review and claiming that Waun Mawn had nothing whatsoever to do with Stonehenge?  I doubt that very much too -- because to cover the story would be to admit to their own gullibility and lack of scrutiny when they published all that tosh about the "Lost Circle" just three years ago.