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Friday, 13 April 2018

The arguments against the glacial transport hypothesis



I spend so much time on this blog pouring cold water on the human transport thesis that we might get the impression that the glacial transport thesis is never actually argued about, except in our comments  section.  In fact the matter of glacial transport is nowadays mostly ignored by the archaeologists,  who presumably want to maintain the pretence that nobody with an ounce of common sense bothers to talk about it since it is now deemed to have been impossible.

But there have been occasions in the not-too-distant past when the archaeologists (and their geological friends) have actually tackled the glacial transport issue head on -- and all credit to them for doing that.  The most intelligent and carefully considered article was published in 2011, as an update to a conference paper presented in 2008.  I did a post about this in 2014, but since debate is always to be encouraged, here it is again  -- even more relevant now, maybe, following all the recent fuss about "Neolithic quarries" and many other matters.

Below I give some extracts from the paper and the comments I added when this was first published.  Still all very relevant.

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The "discrediting" of the glacial transport theory? Hmmm...

https://brian-mountainman.blogspot.co.uk/2014/09/the-discrediting-of-glacial-transport.html

Thanks to Rob for sending me a copy of the following paper, published in 2011 but apparently based on a 2008 conference presentation -- and presumably updated for publication. It's a real curate's egg of a paper, but to the credit of the authors it does at least address the glacial transport theory rather than simply ignoring it!

Much of what is in the paper ifs familiar to followers of this blog. Here is the key info:

STONEHENGE: CONTROVERSIES OF THE BLUESTONES
Mike Parker Pearson (Department of Archaeology, University of Sheffield).
Joshua Pollard (Department of Archaeology, University of Southampton).
Colin Richards (School of Arts, Histories and Cultures, University of Manchester).
Julian Thomas (School of Arts, Histories and Cultures, University of Manchester).
Kate Welham (School of Conservation Sciences, Bournemouth University).
Richard Bevins (National Museum of Wales, Cardiff).
Robert Ixer (Freelance geological consultant, Sutton Coldfield).
Peter Marshall (Honorary lecturer, University of Sheffield).
Andrew Chamberlain (Department of Archaeology, University of Sheffield).


MENGA M
JOURNAL OF ANDALUSIAN PREHISTORY
No 1, 01 // 2011, pp 219-252

Summary

Whilst the sarsen stones of Stonehenge were brought from a short distance of about 30km away, the smaller bluestones originate in Wales, over 200km to the west. This remarkable distance for the movement of megaliths is unparalleled anywhere in the prehistoric world; some geologists have suggested that the bluestones were carried by glaciers in a previous Ice Age but others point out that there is no evidence for past glaciations ever having reached Salisbury Plain or even close to it.

This paper proposes that the bluestones were dragged by Neolithic people around 3000 BC, taking a largely overland route except for a crossing of the River Severn. This contrasts with the conventional thinking that the stones were carried on boats across the sea from Milford Haven in south Wales to southeast England. It presents evidence for new sources of some of the bluestones on the northern lanks of the Preseli hills, as well as rejecting the long-held notion that the sandstone Altar Stone came from the area of Milford Haven. Finally, it proposes that the Preseli bluestones were selected for transport to Stonehenge because they represented the ancestry of one line of Britain’s earliest farming migrants who arrived in the Preseli region shortly before 4000 BC.


Comment: The early part of the paper deals with the geology of the bluestones at Stonehenge and suggests matches with outcrops at many sites in West Wales -- and particularly at Carngoedog and Craig Rhosyfelin. (Note that this paper was written before the first digging season at Rhosyfelin in Sept 2011). This is not exactly a balanced discussion -- there is a very strong "quarry hunting" component to it, as there is in most of the other recent presentations from the archaeologists. At any rate, the thesis is that the bluestones were taken from West Wales to Stonehenge around 5,000 years ago and were first incorporated into Bluestonehenge prior to a further phase of use at Stonehenge itself. That of course is all fantasy, and there is no support for it on the ground, but that doesn't deter your average archaeologist these days........... I would also take issue with the rather partial discussion of erratic occurrences on Salisbury Plain, with "inconvenient" evidence (for example, relating to the Boles Barrow bluestone boulder and the sandstone chip in the Cursus) simply being dismissed as "unreliable". Contrast this assessment with that of Olwen Williams-Thorpe and her colleagues in two big 1991 papers.

There follows a discussion of the possible transport routes used by our heroic Neolithic ancestors -- it is completely fanciful, and the chosen route is the "A40" road route recently favoured by MPP rather than any route involving long sea journeys. Suffice to say that not a single piece of evidence is adduced in support of this idea.........



Now then. To the nitty gritty. Extract:

7. THE GLACIAL HYPOTHESIS

Not all scholars have been satisfied that the bluestones were brought to Wessex by Neolithic
people. In 1902, William Judd proposed that the bluestones might have been transported to
Stonehenge by glaciers during a previous Ice Age. More recently, Kellaway identified the surviving traces of glacial sequences deposited on the east side of the Bristol Channel around Bristol and Bath, perhaps during the Anglian glaciation around 450,000 years BP (1971). He subsequently modified his theory to suggest that the bluestones might have been moved during an episode of glaciation in the Pliocene, 2.47 million years ago, carried southeastwards from Preseli towards Salisbury Plain in the ice of a hypothesised prehistoric river (1991; 2002).

Yet the evidence for glacially derived material in the area around Salisbury Plain is still lacking. Green (1973) concluded from his study of pebbles in fluvial deposits of the rivers Wylie and Avon that there is a complete lack of glacially derived material in these river gravels. There is no evidence that any glaciers ever reached Salisbury Plain during any previous glaciation (Clark et al., in press). 1


Comment: As pointed out elsewhere on this blog, Green's evidence is highly equivocal. He did find erratics in river gravels, but simply assumed that they had come from post-Cretaceous rocks which once capped the chalk and which have subsequently been removed by erosion. There is evidence that glaciers might have reached Salisbury Plain at one stage -- 43 erratic bluestones and other "foreign" debris as well. And glacial modelling also shows that a glacial invasion of the chalk downs was perfectly possible from a glaciological point of view.

The glacial hypothesis is strongly supported by some (Thorpe et al., 1991; Burl, 2006: 145; John, 2008). There is, indeed, evidence for glaciation across a region stretching from the Isles of Scilly to the Bristol region and further north. Even so, it is estimated that any bluestone glacial erratics would not have been deposited closer to Stonehenge than 70km (40 miles) to its west, within the Severn valley in the area of Somerset. Any such bluestones would have still required human transport to bring them to Stonehenge, travelling a distance at least twice as long as that over which the sarsens were transported.

Various aspects of the archaeological evidence are taken as support for the glacial hypothesis
(Williams-Thorpe et al., 1997):

1. The builders of Stonehenge made no careful selection of bluestones to ensure geological
consistency. There may be as many as 13 ‘foreign’ rock types at Stonehenge, many still not identified to source within Wales and one perhaps being an otherwise unrecognised limestone monolith.

2. The inclusion of softer monoliths (such as the Altar Stone) is illogical, given that the harder
stones would have been much better suited to long-distance human transport.

3. If bluestones were so special, why were they not treated with care within the Stonehenge
landscape? For example, bluestone chippings from Early Bronze Age round barrows (2200-1500 BC) have been found only in the fills of the mounds rather than being placed as valuable artefacts within the central graves.

4. The distribution of Neolithic-Bronze Age artefacts of spotted dolerite is spread across
Wales, with a second concentration on Salisbury Plain and along England’s south coast. This second concentration could derive not from long-distance trade but from a local source of glacial erratics.

Each of these queries can be countered. It may be that the different geographical areas represented by the varying lithologies present at Stonehenge were significant because they symbolised the places of origin of those communities taking part in the enterprise. This could also explain why softer sandstone (the Altar Stone) was transported along with harder rocks. If the bluestones arrived at Stonehenge shortly after 3000 BC, there is no guarantee that their chippings would have had any cultural significance a thousand years later when round barrows were built. In addition, it may be that the monoliths themselves, rather than their ‘off- cuts’, were what counted in people’s minds. Finally, the distribution of spotted dolerite artefacts in southern England is likely to derive not from a local source of glacial erratics but from Stonehenge itself; Darvill and Wainwright’s 2008 excavation recovered evidence for prehistoric stone tool manufacture from worked-down bluestones (Tim Darvill pers. comm.). Stonehenge was thus the likely ‘quarry’ from which the southern English bluestone tools originated.

There are four further, major reasons why the glacial hypothesis, which argues the presence of a source of glacial erratics in the Somerset area, is likely to be flawed:

1. There are plenty of suitable stones from which monoliths could have been fashioned in the
environs of Stonehenge, considerably closer than 70km away – the supposed source of bluestone erratics. For example, the SRP’s excavations of the Cuckoo Stone and the Tor Stone at Bulford, both within a few kilometres of Stonehenge, located the solution hollows in which each of these stones had lain, thus demonstrating their local provenance. If proximity and minimal effort were the main principles for selecting Stonehenge’s stones, why bother to go as far as 70km to the west?

Comment: This is a circular argument. If the bluestones were lying around in the Stonehenge landscape, as is perfectly possible, of course they would be used for incorporation into a developing megalithic structure. We don't know whether the bluestones always were separated from the sarsens -- in some settings they might have been mixed up. And where did this idea come from that there cannot possibly have been any glacial erratics closer than 70 kms from Stonehenge? True, I have mentioned the occurrence of glacial deposits at Greylake and other sites in Somerset, and speculated about a possible ice edge near Glastonbury or near Westbury, on the chalk escarpment, but I have never doubted that the ice from the Irish Sea Glacier COULD have pushed a lot further to the east.

2. The stone circles and standing stones at Stanton Drew in Somerset, likely to date to the Neolithic, are close to the putative source of glacial erratics. Yet there is not a single bluestone among their varied lithologies, even though many of them were probably brought several kilometres to that site.

Comment: This is a flawed argument. The stones at Stanton Drew may or may not be glacial erratics, but the ice stream that affected the northern flank of the Mendips was not necessarily carrying the same assemblage of erratics as the ice that passed to the south. See my recent post on this.

3.The new evidence for bluestones in Stonehenge’s first phase indicates that primarily
bluestones, rather than sarsens, were acceptable to Stonehenge’s builders in 3000-2920 cal BC. This would suggest that the question of the type of stone was a matter of considerable concern for the Neolithic builders.

Comment: What "new evidence for bluestones"? Is this a reference to the non-evidence from Bluestonehenge? I don't accept that only bluestones were used in the early "bluestone settings" -- where are the facts that point to this?

4. The specific pillar-shaped monoliths selected for Stonehenge form only a tiny proportion of the available blocks of natural rock in the various outcrops of Preseli and its environs. The vast
majority of out-cropping stone is of blockier material unsuitable for detaching from the rock
outcrops as thin, 2m-4m-long natural monoliths. If bluestones were transported by glaciers as ‘free boulders’ (rather than smaller-sized erratic material; Thorpe et al., 1991: 148), the significant proportion of pillar stones at Stonehenge is at odds with the more varied boulder shapes to be expected as glacial erratics, deriving from the blocky material of the majority of Preseli outcrops.

Comment: This is a strange argument. Of course the bulk of broken stone around the tors of the Preseli district is blocky or chunky -- rather than pillar-shaped -- but I do not accept that the bulk of the bluestones at Stonehenge are long thin monoliths. Look at them carefully, folks. They are in all shapes and sizes, ranging from pillars to slabs to boulders -- and of the 43 we know about, we can only speculate on those which remain just as stumps. We cannot simply assume that those were pillar-shaped, just to suit somebody's hypothesis. And we don't know how many "inconvenient boulders" might simply have been destroyed or turned into axes.

In conclusion, although the glacial hypothesis remains unfalsified and cannot be rejected, most archaeological scholars consider human agency to have been the more likely cause of the bluestones’ movement. The debate between supporters of the two opposing theories has been vigorous and even intemperate; only further research at the source outcrops will resolve whether the bluestones were plucked by glacial action or quarried by Neolithic megalith-builders.

Comment: Having demolished the glacial transport hypothesis to their own satisfaction, the authors then say: "There are two current hypotheses to explain why the bluestones were brought by human
agency from south Wales." They summarise the "healing stones" hypothesis of Darvill and Wainwright and the "ancestor stone" hypothesis of MPP and his colleagues -- coming down heavily (as one might expect) in favour of the latter. So the emphasis here is on the "why" and not the "how" -- as the essential correctness of the human transport thesis is simply accepted as fact. That is just not good enough -- what's sauce for the goose is sauce for the gander. If this is supposed to be a balanced assessment of competing theories, where is the itemisation of the flaws in the human transport hypothesis to match the itemisation of the supposed flaws in the glacial alternative? Let me help:

1. There is no sound evidence from anywhere in the British Neolithic / Bronze Age record of large stones being hauled over long distances for incorporation in a megalithic monument.

2. The builders of Neolithic monuments across the UK simply used whatever large stones were at hand.

3. If ancestor stones were being transported to Stonehenge, why have all of the known bluestones come from the west, and not from any other points of the compass?

4. There is no evidence either from West Wales or from anywhere else of bluestones (or spotted dolerite in particular) being used preferentially in megalithic monuments, or revered in any way.

5. If long-distance stone haulage was "the great thing" for the builders of Stonehenge, why is there no evidence of the development of the appropriate haulage technology leading up to the late Neolithic, and a decline afterwards? It is a complete technological aberration.

6. The evidence for quarrying activity in key locations is questionable, to put it mildly.

7. The sheer variety of bluestone types (I still insist the figure is somewhere near 30) argues against selection and human transport. There cannot possibly have been up to 30 "bluestone quarries" scattered about West Wales.

8. No physical evidence has ever been found of ropes, rollers, trackways, sledges, abandoned stones, quarrymen's camps, or anything else that might bolster the hypothesis.

9. Bits and pieces of experimental archaeology on stone haulage techniques (normally in "ideal" conditions) have done nothing to show that our ancestors could cope with the sheer physical difficulty of stone haulage across the heavily-wooded Neolithic terrain of West Wales (characterised by bogs, cataracts, steep slopes and very few clearings) or around the rocky coast. Aubrey Burl made this point forcefully many years ago, and it remains forceful today.

10. And if there was a "proto-Stonehenge" somewhere, built of assorted local stones and then dismantled and taken off to Stonehenge, where was it? Herbert Thomas thought it might have been near Cilymaenllwyd (south of Preseli) and now MPP thinks it might have been north of Preseli, either at Waun Mawn or Castell Mawr). So the great proto-Stonehenge hunt continues.......

.... and so on. To repeat. There is no evidence.

In conclusion, all credit to the authors for at least having a look at this issue in a nicely-presented paper, but a little more balance would not have come amiss.

1 comment:

TonyH said...

Westbury (near where I live) is a lot closer than than 70 kms from Stonehenge. I think they have been regurgitating your mention of Greylake and Glastonbury.