More on stone shapes

This is the simplest type of stone shape analysis -- it can help to determine the nature of the deposit you are looking at. The technique is to collect 50 or 100 stones / pebbles fragments in a determined size range, and then visually classify them into the 4 categories. Then express as percentages on the histogram. The histograms show some work I did for my doctorate, back in 1963! Note that the "head" (a periglacial slope deposit) (A) has a clear peak in the angular category. The two types of till (B and C) have peaks in the sub-angular category. The fluvioglacial sands and gravels (D) have more rounded and sub-rounded pebbles and few angular ones.

Simple stuff, but quite helpful...... now how about something similar for Stonehenge, and all those pebbles and flakes in the ground?

If the great majority of fragments of bluestone are sharp-edged and angular, that would of course support the contention that they are for the most part flakes bashed off the bluestones in the process of dressing. But even if this is "dressing debris" one might expect parts of the stones to be smooth or weathered, representing the outer and exposed surfaces of the original monoliths and boulders.

Bluestone fragments galore

I'm increasingly intrigued by the super-abundance of "bluestone" fragments (ie fragments of rock other than sarsen, chalk and flint) within and around the stone settings at Stonehenge, and the fact that they also pop up elsewhere -- in the Cursus and other digs on which the geologists have been called in to do lithological identifications.

The Stonehenge Layer is rather intriguing.......

With ref to the Darvill / Wainwright dig in April 2008: "The dig also investigated the “Stonehenge Layer”, a significant and varied layer of debris and stone chippings spreading across the whole extent of the stone circle and comprising a high proportion of bluestone fragments. This is the first time that the nature, content and structure of this layer has been properly studied, crucially to determine whether this deposit was derived mainly from the construction or destruction of the Double Bluestone Circle and of Stonehenge as a whole."

We see references to debris, chippings, fragments, flakes etc -- and there is a consensus that many of these bits and pieces have come from the working of the bluestones on the site. But do all of the fragments match up with known stones or stumps on the site? Are some of the rock types identified found only as fragments? Could they therefore be either intact bits of erratic debris or the remains of smaller erratics that have been broken down?

The question "Where are all of the small erratics?" is asked quite frequently -- and I wonder if they have been there all the time, in the Stonehenge Layer and maybe in the undisturbed soils of Salisbury Plain? Does anybody have any clues that they might wish to share?

Hauling bluestones through the jungle

The terrain west of Efailwen and south of Llangolman -- precisely the territory that the bluestones would have had to be transported across. Remember that in the Neolithic the fields would not have been clear -- there would have been dense "virgin forest" everywhere, except in the natural clearings where there might have been thin soils and rocky terrain, or else string bogs. Transporting monoliths across this terrain of steep gradients, chaotic woodlands and turbulent streams? The word "impossible" springs to mind......

In the last couple of weeks I have driven a few times through the landscape to the south of the Preseli Hills -- with a series of deeply-incised streams belonging for the most part to the Eastern Cleddau river system -- and have marvelled at the rough beauty of the place. The valleys are heavily wooded to this day, with tumbling streams and rapids, shallows and pools, and boggy and rocky areas adding to the number of ecological niches.

That got me thinking about the sheer daftness of the idea that a single large bluestone monolith -- let alone more than 80 -- could have been dragged through this terrain from the Carn Meini area to the head of navigation at Blackpool Mill. this is what I put in Ch 8 of my book:

".........the ill-fated "Millennium Stone" project in Pembrokeshire (in the year 2000) showed that even with the aid of cranes, tractors, modern ropes and low-friction netting on the ground surface, the transport of a single bluestone monolith over rough terrain was incredibly difficult. And the organizers did not even take the stone from a natural rock outcrop surrounded by scree and boggy land. They took it from a farmer’s field close to the road. They did not dare to pull the stone across country, through fields, bogs and wooded areas, but stuck to roadways for the 27 km or so of the sled pull. They had the advantage of good maps which could be used for the avoidance of steep gradients as far as possible. In contrast, our imaginary Neolithic stone collection teams would have had to cope with a heavily wooded landscape which would have been as difficult to pass through as the west coast rain forest of New Zealand. Any team hauling a heavy stone would have encountered, over and again, boggy areas too wet to haul sledges across and too shallow for rafts or boats. And how would they have found their way to the head of navigation of the Eastern Cleddau? Only by finding the river and following it downstream -- and in the process having to cope with the most difficult physical conditions imaginable."

I am reminded of the work I did once as a geography student, on terrain roughness. There was a roughness index -- and as far as I know there still is. The Eastern Cleddau catchment will be well up on the roughness index -- and Salisbury Plain will be somewhere at the other end of the scale. Moving stones there would have been almost a doddle -- if the land was reasonably clear of trees.

In am often gobsmacked by the sheer naivety of archaeologists who look at the Atkinson stone haulage experiments (on the nice smooth chalklands of Salisbury Plain) or the assorted stone movement experiments so graphically illustrated on YouTube, and then say "Oh yes, it has been proved that it was possible to move large stones over long distances.........." Sorry, folks. Not on this terrain, it hasn't.

Another bluestone mystery

A few years ago I was hunting for "bluestone" regferences, when I came across an ancient reference (from John Leland) to abundant blue stones being used in early buildings at South Cadbury (or Arthur's Camelot, if you prefer). This is an Iron Age hillfort, used again later on in the Dark Ages. Could "bluestones" from Preseli or elsewhere have been used in the construction of the original hillfort? Or was the blue stone more local? It seems most likely that the latter was the case. I got these helpful replies to my enquiries:

1. "I think that the "dusky blue stone" referred to by Leland must be the local Blue Lias. There aren't any igneous rocks in that area that might have been used as building stone. You can find some information in the excavation report if you are able to get hold of a copy: "John C Barrett, P W M Freeman and Ann Woodward 2000, Cadbury Castle, Somerset: The later prehistoric and early historic archaeology, English Heritage Arch Report 20". There is a map of the local geology on page 9, which shows where the Lias outcrops and also a little about building stone on page 267. I hope that this might, belatedly, be helpful". With best wishes, Fiona Roe.

2. "You are probably right in interpreting Leland's rather vague comments as referring to Lias. There is an outcrop to the west of the hillfort and it was used as building material from the Roman period onward - mainly by them for roof tiles as it breaks in a flat plane. The walls that Leland saw would have been the Late Saxon refortifications that you can still see eroding out of the inner bank, they are mostly the local yellow sandy limestone, but reused other stuff that was lying about. Excavations around the hill have over the last few years turned up burnt stone that goes a bright blue or red colour, and in some cases seems to have been selected for particular purposes based on colour". Hope that helps, Clare Randall.

Olwen Williams-Thorpe once looked for foreign stones around South Cadbury, but discovered none that she could be certain about. Rob Ixer also reminded me that there are some local basalts not far away -- not sure what colour they are.......

The Bluestones and Elvis Presley

Thinking of cultural things, there was an equally splendid film made a few years ago, based upon the thesis that Elvis Presley was really a Welshman, and that his family came from the Presely Hills. The name of the family when it emigrated to America was Presely, but was later changed to Presley......

In the film (shown on S4C) a group of ancient rockers went up onto the mountains and pranced about amongst the bluestones, performing a few of the Elvis classics on their guitars and singing away at the tops of their voices. It was totally bizarre and brilliant!

Bringing Back the Bluestones

Went to the theatre last night, to see a very jolly performance of the play called "Bringing Back the Bluestones" -- based on the spoof (which fooled large parts of the media) a few years ago, in which a little group of locals started a campaign to get the bluestones all returned from Stonehenge to Preseli, citing in support of their claim the Stone of Skone and the Elgin Marbles......

It was all in there -- the mystical significance of the site, ley-lines, Druids, English Heritage, and rich Americans waving cheque books.

.... and Henry Hicks was even smarter

Henry Hicks (1837-1899)

He was born on the 26th of May 1837 at St Davids in Pembrokeshire, Wales. Following in the footsteps of his father Thomas, he studied medicine...... He practised in St Davids until 1871

Geological career

His interest in geology was first stimulated whilst growing up in Wales, particularly after meeting John William Salter, palaeontologist for the Geological Survey, who was devoted to the study of the rocks and fossils of South Wales.

In 1865, in conjunction with Salter, he established the Menevian group, Middle Cambrian characterized by the trilobite Paradoxides. He then wrote papers on the Cambrian and Lower Silurian rocks, and described many new species of fossils. Later he studied the Pre-Cambrian rocks of St David's where he described the Dimetian (granite) and the Pebidian volcanic rock. He subsequently worked on the Pleistocene deposits of Denbighshire, and then became a leading expert in Devonian rocks, where he was the first person to identify fossils in the Lower Devonian and Silurian Morte slates from Mortehoe in Devon. His observations on ice directions and erratic transport in Pembrokeshire were accurate and astute.

He was elected as a Fellow of the Royal Society F.R.S. in 1885, and was president of the Geological Society of London 1896-1898.

Sir Archie was no fool

An old map showing the proposed ice limits of the "Older Drift" glaciation of Great Britain, according to Sir Archibald Geikie (1894) and Charlesworth (1957)

I found this old map, which I made in 1962 to show the proposed ice limits of Geikie and Charlesworth. Note that Geikie in 1894 had an intuition that the ice coming in from the sea extended all the way up the Bristol Channel and pressed well across the present coastlines of Devon and Somerset. The ice margin out in the Celtic Sea does not make a great deal of sense, given what we know today, but nevertheless this is a pretty impressive piece of deduction on his part, made on the basis of very scanty evidence. He knew that St George's Channel had been occupied by a massive Irish Sea Glacier -- that had already been demonstrated in 1885 by a geologist named Hicks, who recorded striations and erratic movement in the St David's area that could only be explained by ice coming onshore from the NW. In 1891 Hicks also demonstrated that the lowland parts of Pembrokeshire had also been inundated to a great depth by ice coming in from St George's Channel.

Where Geikie went seriously wrong was in his assumptions about the sources of the ice in W and S Wales -- he thought that the ice affecting Devon and Somerset was WELSH ice coming from the north. He also thought that the ice overriding Pembrokeshire was Welsh ice flowing into Cardigan Bay from the uplands, and flowing across the county from NE towards SW. In saying that, he appears to have forgotten the evidence -- already in print -- from Hicks.

The term "Irish Sea Glacier" was coined by Carvill Lewis in 1903. The most important work in the early part of the twentieth century was that of TJ Jehu in 1904 -- he worked out the Pleistocene stratigraphy of North Pembrokeshire, and confirmed that the traces of ice action (striations and erratic transport) all showed a dominant ice flow from NW towards SE.

Given this convincing history of earlier research, it is all the more amazing that HH Thomas, when he proposed his "human transport" theory as an explanation for the presence of bluestones at Stonehenge, dismissed out of hand the idea that ice overrode Pembrokeshire and extended far to the east......... carrying erratics with it.

Bell curves and glacier mechanics

Fresh lodgement till in Iceland. There will be some pretty big spikes in the particle distribution or weight curves for a deposit like this. At a guess, I would say there will be 3 spikes -- one for the silt-clay fraction, one for the cobble fraction and one for the boulder fraction.....

In continuing with debate with Ned Pegler, I have pasted this onto his site:

Good to discuss this, Ned! I think your basis problem is that you have assumes the EVERYTHING IS ERODED, TRANSPORTED AND DUMPED TOGETHER when an area is overridden by glacier ice. That may be so in the grand scheme of things — for example, a gigantic glacial trough is eroded, leading one to conclude that all of the bedrock that was there before is not there any longer, and must therefore have been taken and dumped somewhere else. But actually when you look in detail you see that erosion, entrainment, transport and deposition are all actually very selective, depending on the mechanics involved. So if shearing is involved, you get huge blocks of rock caught up in the glacier, and if abrasion is involved you may get sand, silt and clay fractions carried away, with very little in the way of pebbles and boulders. That is why you get huge variations in the nature of glacial deposits. In some cases a fine-grained till with just a few entrained stones, in some cases “free boulders” or erratics, with virtually no matrix of finer sediments, and in other cases (if there has been flushing by water) virtually all sand and gravel with hardly any silt and clay and (at the other end of the scale) hardly any stones and boulders either. So while all of the rock in a glacial trough may have been removed, it is carried away in different ways, and “redistributed” into different parts of the deposition zone down-glacier. If you then try to make a bell curve of the sediments in any one area, you will end up with bimodal or even multimodal spikes.

I did this sort of work 50 years ago as a research student, and while techniques may have changed between now and then, the principles of sedimentology haven’t! OK?

Letter to Ned -- the glaciers are still winning

Dear Ned,

OK -- let's look at your "Neolithic statistics". Yes -- glaciers can and do pick up material of all shapes and sizes. But your first graph is faulty -- there is not a smooth linear relationship between stone size and frequency. Your Fig 1 is sheer fantasy. In some areas of glacier deposition there may be large quantities of very large boulders and virtually no till or finer matrix. Even in till sheets there may be bimodal peaks on the graphs of particle size. Then you say: "But when the ice sheet finally melts it dumps everything, from grain to boulder, in the same place." That is sheer fantasy too -- glaciers do not do that. They entrain material in ways that are highly variable, depending on basal ice conditions, ice velocity, and the nature of the underlying terrain and lithology. Sometimes the basal ice will hardly move at all, and may be frozen onto the bedrock -- and ice above it will move along shear planes or through internal deformation, carrying entrained material with it.

Next point: " this jumble of rubble will tend fit tidily in one thing though – the statistical bell curve of size distribution by weight." Sorry -- but that is sheer nonsense.

Then: "So the ice sheet will be picking up thousands of tiny pebbles at the same time as it picks up one large boulder." Sorry -- wrong again.

Then: "On the other hand those millions of tiny pebbles, when you weigh them, don’t weigh that much." Oh really? Ned, have you tried to weigh a sheet of lodgement till maybe 10m thick and extending over maybe 100 km2? Come off it! But Fig 2 shows that big stones tend to be heavier than small stones -- statement of the obvious -- are we supposed to be surprised by that?

So to your bell curve (Fig 3) which is supposed to hold the key to this mystery. Is it supposed to show us that the total weight of small stones in a glacial deposit is relatively small, whereas the total weight of medium-sized stones is rather large, and whereas the total weight of very large boulders or monoliths (like the bluestones at Stonehenge) is much smaller again. You seem to think this is an ideal "ice sheet dump distribution". Sorry again, Ned -- but that is fantasy.

Then to the title "Ice sheets lose" -- I would agree that what we have on Salisbury Plain is a graph that would show a series of spikes, for example associated with the bluestone monoliths at Stonehenge, or the massive numbers of bluestone fragments in the "Stonehenge layer". But to suggest that there "should be absolutely thousands of smaller bluestones lying around" is absurd -- as I have explained both in my book and on this blog.

Quote: "Alternatively, if the bluestones were the “average” stone size (B on the bell curve), then there should be much larger stones lying around. There aren’t. Perhaps the Stonehenge builders chopped these larger stones into bits. Maybe. Whatever, even in this case you’d still find a large number of pebbles lying around. You don’t." This all falls down on the faulty assumption which underpins this whole speculative piece. I doubt that you will find a particle size distribution for an area of glacial deposits anywhere in the world that would remotely fit your hypothetical bell curve.

Quote: "Notably, the Neolithic long barrows of Salisbury Plain, which are older than Stonehenge, do not include one single one of these theoretical large bluestone boulders in their construction." Wrong -- Boles Barrow did contain a bluestone boulder, and for all we know there may be other bluestone boulders in other long barrows as yet unexcavated.

Your heading: "People win… at least partly." I beg to differ -- the glaciers are still winning.

Contrary to what you seem to think, Ned, you have not demolished the idea of glacial transport and glacial deposition, since your hypothesis is based on faulty mathematical modelling. Please go off and read some of the abundant text books on glacial deposition and the nature of glacial sediments, and then maybe have a fresh look at the problem.

Bluestones and mathematics

Now this is an interesting little piece, designed to prove that the bluestones on Salisbury Plain cannot be glacial erratics.

Bluestones & Bell Curves
On April 5, 2010, in Theories, Thoughts and Essays

Special guest post by EDWARD PEGLAR (from ARMCHAIR PREHISTORY)
How didn’t the Preseli bluestones get to Stonehenge?
Ask your maths teacher.

http://standingstones.tv/theories-thoughts-essays/bluestones-bell-curves/

Must do a bit of gardening while the weather is so fantastic -- but later I will explain why I have severe reservations about this mathematical "proof"........ largely based on the fact that Ned has got his assumptions all wrong.

Ask your maths teacher? On balance I think I would prefer to ask a glacial geomorphologist.

webring

Powered by WebRing.

Where are all the polishing stones?

Polishing stone on Fyfield Down (from Celia Haddon's site:
http://www.celiahaddon.co.uk/standing%20stones/wiltshire.html)

Pete G has raised an interesting point. If the bluestones and sarsens were transported for great distances overland, there must have been a need for hundreds --- if not thousands -- of rollers or heavy timbers for sledges. That means many thousands of trees felled. That means many thousands of stone axes and other stone implements, which needed sharpening and smoothing. So where are all the polissoirs or sharpening stones? Pete mentioned this one to me:

Quote from Celia: THE POLISHER STONE, FIFIELD DOWN. SU 128 715
Up from Avebury along the Ridgeway towards Barberry castle, just past boundary stones on the side of the track and near the head of a gallop. Said to be a Neolithic stone, used for polishing stone axes, but I don't know how the grooves can be dated exactly. It could have been used to strop shepherd's tools later in history rather than prehistory. Julian Cope says it is estimated to have been used for 1,200 years (see his Modern Antiquarian book).

There is another one in Leafield in Oxfordshire (LEAFIELD SP 316 153). But where are the hundred of others that we might expect in and around Stonehenge and (if the stones were carried by our heroic ancestors from Mynydd Preseli)in eastern Pembrokeshire?

Part of the problem, of course, is to know which grooves and hollows are prehistoric, and which date from recent times, when farm labourers needed to sharpen their scythes and sickles on suitable stones close to the places where they were working....

Dancing with the Dartmoor fairies

Coverage in the media today -- fed by a British Archaeology press release -- about "nine megaliths" on Dartmoor -- including sites at Cut Hill and Drizzlecombe. Apparently the stones "are aligned to mark the rising of the midsummer sun and the setting of the midwinter sun." They (the stones) have all now fallen over, but the settings date from around 3,500 BC -- ie older than Stonehenge and about the same age as Boles Barrow and other long barrows in southern England.

So far so good -- but in his comments, journal Editor Mike Pitts then goes off on a bizarre tangent to talk about feasting and barbequed pigs near Stonehenge. One might wonder what this has to do with fallen-over monoliths on Dartmoor -- but there is no stopping our esteemed Editor. He continues: "At Stonehenge,the dark navy-colored bluestones may themselves represent ancestors or spirits from the underworld, while the big orangey-pink (before weathering) sarsens could reflect summer and light." Hmmm. Oh yes? But there's no stopping him once he is in his stride! He claims that several standing stone monuments (where? he doesn't say) held ritualistic meaning. He then likens their construction to the building of cathedrals and pyramids, and to the carving of the giant heads on Easter Island. All, he says, are involved in the "defining of ritual spaces, giving ceremony and power distinctive physical presences, engaging large numbers by employing them in the construction processes, ceremonializing places beyond the mere moment of the rituals."

And all this from a few fallen-down monoliths on Dartmoor! Not so long ago a very senior archaeologist accused Wainwright and Darvill of being "out with the fairies." Who's out with the fairies this time?

The Last Glaciation of the Bristol Channel

O Cofaigh and Evans, 2007 -- LGM or maximum advance of British-Irish ice into the Celtic Sea:

From the Abstract: "The Irish Sea Till was deposited by the Irish Sea Ice Stream during its last advance into the Celtic Sea. We present 26, stratigraphically well constrained, new AMS radiocarbon dates on glacially transported marine shells from the Irish Sea Till in
southern Ireland, which constrain the maximum age of this advance. The youngest of these dates indicate that the BIIS advanced to its overall maximum limit in the Celtic Sea after 26,000–20,000 14Cyr BP, thus during the last glaciation. The most extensive phase of BIIS growth therefore appears to have occurred during the LGM, at least along the Celtic Sea and Irish margins. These data further demonstrate that the uppermost inland glacial tills, from the area of supposed ‘‘older drift’’ in southern Ireland, a region previously regarded as having been unglaciated during the LGM also date from the last glaciation."

I disagree strongly with this ice margin as it is portrayed in the Bristol Channel and in West Wales. Ice always moves perpendicular to the ice margin except where there is an exceptionally strong physical constraint. So the ice cannot have flowed from NE to SW along the Pembs coast -- it must have come in from the NW, flowing towards SE. That is exactly what the ground evidence says -- when one looks at striations and erratic transport. All of the ice that laid down the latest Irish Sea till deposits around the Pembs coast came in from the NW. And I cannot imagine an ice-free Bristol Channel either -- an ice lobe like this MUST have reached the coasts of Cornwall, Devon and Somerset around 20,000 years ago, even if the ice stream was behaving like a surging glacier and even if it had an exceptionally low long profile (ie a profile very different from the glacier "equilibrium profile".) Colm and David do discuss this as a possibility -- but I think they should have adjusted the ice margin on the map while they were about it!!

What has this got to do with Stonehenge and the bluestone erratics? Not a lot really -- except to flag up the idea of repeated glaciations, with relatively minor differences in ice flow directions.

More on erratic trains -- Canada

An old message (2007) from Lynda Dredge:

Most of my research has been done in the north over more subdued Shield and limestone landscapes. Most of the erratics that I have traced as “trains” are smaller limestone-sourced blocks being transported over granitic terrain. (Most of my work on this was in Manitoba west of Hudson Bay and farther north, around Foxe Basin/Baffin Island.) The smaller size of the boulders would partly be due to the ease of comminution of the limestone, and splitting of the erratics along the limestone bedding planes. I have found that the limestone blocks (as well as carbonate matrix) have traveled more than 75 km, and the matrix material much farther, up to several hundred km. (see Dredge, 2000, Boreas: 144-156 for example). The dispersal trains in the Melville Peninsula and Manitoba examples (Can J of Earth Sciences, 1988) are quite broad, but within them are secondary dispersal plumes and erratic trains with exceedingly sharp lateral limits. The trains are relatively narrow – more like 300 m across. I have attributed these plumes to ice streams within a larger ice sheet.

This is a situation very close to that which Lionel Jackson and I have speculated about for the Irish Sea ice stream coming into Somerset.

The Stonehenge stones -- cheap and local, or expensive and exotic?

Good old-fashioned opportunism -- the gravestones in Flimston Churchyard, south Pembrokeshire, are almost all made from glacial erratics carried from NW Pembrokeshire.

Back to the issue of recycled stones and boulders littering the landscape. I thought I should share this -- came across it when looking back through my records. What I particularly like is that Stephen stresses the importance of opportunism, utilitarianism and scavenging amongst prehistoric peoples -- of course they would use stones that just happened to be around them quite instinctively, simply in order to minimise effort. The romantic vision of all stones being invested with significance, AND THEREFORE WORTH TRAVELLING HUNDREDS OF MILES TO OBTAIN, is hogwash. It may have happened on extremely rare occasions, if a particular stone was particularly valuable for axe making, for example, but in general "economy of effort" must have been the guiding principle, both with respect to monoliths for building megalithic structures, and for the manufacture of small artifacts.

Stephen Briggs.
ERRATICS AND RECYCLED STONE IN PREHISTORIC BRITAIN AND BEYOND: SCHOLARLY IRRELEVANCIES OR FUNDAMENTAL UTILITIES?

2007 Conference abstracts
ABSTRACTS FOR ORAL PRESENTATIONS, POSTERS, & STAND-ALONE POWERPOINT PRESENTATIONS:

http://implementpetrology.org/conferences/2007/abstracts.html

Nineteenth-century Britain saw the birth of archaeology and geology. Both were rapidly subdivided; the idea of prehistory only being accepted after c 1860, while from the 1820s glaciation was a key problem for pre-Darwinian scientists to fathom. Once glaciation became fact, a popular movement developed to collect and identify erratics, in Britain from c 1870-1914. Vast numbers of erratics were also identified or collected throughout Europe, with particular interest paid to Scandinavian and Alpine rock-types. Current views on glacial direction and extent are still largely based on this work because collecting and identifying re-cycled stone long since ceased to be fashionable. Other earth processes can also re-cycle stone long distances in quantity. In Europe the Bunter pebble-beds at the base of the Triassic are a good example. Their content in Britain probably has a bearing on the origins of 'Cornish greenstone axes'.

Early artefact petrographic identifications studies drew heavily on the evidence of re-cycled stone, at a time when prehistoric peoples were seen as scavengers. With the establishment of routine implement petrography came the (more attractive) notion of trade, but because it was very difficult to interpret some distributions in commercial terms, more sophisticated theories of behaviour developed. And as theory expanded to include the social and spiritual motivation of primitive peoples, the potential value re-cycled stone was eventually lost sight of. Indeed, some prehistorians nowadays argue that prehistoric peoples ignored accessible usable materials in favour of those brought from distant sources because the carry different 'identities'. Thus, this aspect of prehistory has passed from an evidence-based empirical study to occupy a firm place in post-Modernist academe.

Whereas the petrographic identities of many implements are now known in great detail, no comparable quantitative or qualitative data exists for re-cycled stone such as glacial erratic. This inbalance in knowledge can only be addressed if the public is persuaded to attach greater value to collecting stray stones and museums are willing to identify them. There is no reason why the scientific skills brought to bear on artefact studies should not equally profit from studying re-cycled stone. Pursued in tandem, the two studies can only enhance both archaeological and geological knowledge and gain the confidence of a public keen to see the return of respectful debate to our branch of learning.

Pembrokeshire erratic routes

I discovered this old map from the days when I was a research student -- back in 1963! It's based on Griffiths's work -- there are many erratic trails across the county, and not all of the traceable arratics are from the Mynydd Preseli area. Note that some very recognizeable erratics come from St David's Peninsula too......

The ice movements are "aggregate" movements -- of course, we do not know how many times erratics have been lifted and moved by ice, sometimes in directions significantly different from those shown on the map. Neither do we know how many glacial episodes are responsible for moving the erratics from source to "final resting place."

The Stonehenge Stone-stealers

Boles Barrow, near Heytesbury, on the western edge of Salisbury Plain, in 1979. Much battered by the Army. Was the Boles Barrow bluestone the one that got away?


Referring back to one of my earlier posts:

Geoffrey Kellaway argues strongly that the bluestones which were used in the stone settings at Stonehenge were all stolen or removed from earlier stone settings -- monoliths, dolmens, long barrows -- as part of the Stonehenge enterprise. That would of course accord with the MPP theory of the Bluestonehenge stones being removed (with reverence or irreverence) from that place to Stonehenge itself. Geoff argues that the reason for this "stone stealing" was that the bluestones always were in short supply, and that they never had enough of them to finish the job (whatever that might have been....) Maybe there was a lot of "stone stealing" happening with the sarsens as well......

He thinks the Boles Barrow bluestone was "the one that got away" -- maybe because it was a bit too far from Stonehenge for the builders to bother with. He also thinks there were bluestones (large and small) all over the place, including the Stonehenge neighbourhood, the Cursus, the Boles Barrow area, and Normanton Barrows. He says that Cunnington found a piece of bluestone in the Normanton barrow that had previously been examined by Stukeley. He also reminded us of Cunnington's conclusion that "these pieces (of bluestone) were scattered about on the plain before the erection of the tumuli under which they have been found." Not sure what the stratigraphic evidence for that is -- you would need to find in situ or undisturbed sediments beneath made-up ground with an archaeological identity.

What independent evidence is there that pre-Stonehenge burial mounds / long barrows have been destroyed or interfered with during "stone stealing" excavations?

Stonehenge packing stones

This is a nice pic from the Atkinson era of one of the packing stones unearthed during excavations. Not sure what type it is -- presumably one of the limestones or sandstones assumed to have come from the fringes of Salisbury plain. On the other hand it may be sarsen -- and archaeologists have always assumed that smallish boulders and lumps of sarsen, found in the immediate locality, were used as mauls, heavy grinding stones and as packing stones. Most of the smaller hammer-stones were made of flint. There is endless dispute over how much "dressing and shaping" actually went on -- Atkinson and others speculate on millions of man-hours being involved. Some of the sarsens appear to be "well-dressed" and others are in their pristine or natural state.

I don't think there has ever been a systematic study or quantification of these "extraneous" or "rubbish" stones, since the focus of attention has always been on the standing stones or monoliths, and the lintels. But there are very many "exotics" in this packing rubble, and we should all examine them more carefully for clues as to the origins of the monument.

The rocks found at Stanton Drew

On checking back with my old posts, I found this from last October.

re the geology of the Stanton Drew stones, Geoff Kellaway said that the ice that crossed the Stanton Drew site came from the NW -- it crossed Broadfield Down, eroding the Lower Lias. It carried boulders of Upper ORS from the Failand Ridge, and entrained masses of Triassic conglomerate and Lower Lias breccia from Winford and Felton, and also picked up slabs of Dundry Freestone.

The builders of Stanton Drew used a litter of boulders of all these rock types -- they were opportunists and foragers who (naturally enough) simply wanted to minimise effort.

Is there any other geology that confirms or disputes Kellaway's identifications?

Bluestonehenge -- and The stones of Stanton Drew

I came across this from Dennis's Eternal Idol site:

With ref to Bluestonehenge and Mike Parker Pearson, Oct 13th 2009 (Report by Alex)

Extract:
Human agency, or glaciation?

"The two monuments at Stonehenge and Bluestonehenge both show an impressive collection of bluestones. We know they came from Wales, but how did they arrive? While acknowledging that current research is casting new light on glaciation, Mike still prefers the idea of human agency. He referred to the latest article in British Archaeology from Rob Ixer, that relocates the source of many of the stones away from Carn Meini, the traditional source, preferring Carn Goedog, for instance for the source of the spotted dolerites, because of a closer chemical match.

Mike’s opinion gained from his glaciation experts is that potential bluestone-carrying glaciations would have come no closer than about 50 miles, dropping their load in the area of Somerset and Gloucestershire. So what evidence is there for bluestones in that area?

There we find Stanton Drew, a massive henge that incorporates stones of varied geology that have been imported from many miles away. But there isn’t a single bluestone there. Mike feels that if glaciations were a factor, then bluestones would inevitably have been used at Stanton Drew. They haven’t – and that destroys the credibility of the glacier-borne theory.

So did the Neolithic people transport the stones by water or land? For Mike, they’d have done anything to avoid the uncertainties of a water route. In short, he believes that – “it’s the labour that counts” – and that work gangs would have competed eagerly for the prestige of the heaviest stones or the greatest distance."

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

Hmmm -- I think I would dispute quite a lot of that. For a start, Bluestonehenge does not show an impressive collection of bluestones, and probably never did. What we have is a collection of sockets, with no evidence whatsoever as to what might have been in them. We do not know that they came from Wales, since we have no stones -- just speculation. The stones could just as well have been sarsens. I wonder who Mike's glaciation experts are? Are they glaciologists or geomorphologists? Come out into the open, you guys! Let's see the colour of your eyes! That having been said, we can have a debate about whether the ice that came into Somerset got closer than 50 miles away from Stonehenge. All evidence gratefully received. That is exactly what I am trying to sort out in this blog.

Stanton Drew? Why should bluestones (or rocks from Preseli) have been used there? As I have said before, Stanton Drew lies to the north of the Mendips, and there is every reason to think that the ice stream that affected that area may have contained erratics carried by Welsh ice or ice that came down the Severn valley. The lack of bluestones at Stanton Drew does NOT "destroy the credibility of the glacier-borne theory." In fact, it supports one of the arguments used by Kellaway.

... and if you are cursed, I can make you better!

A few years ago, I played the part (not very well, it has to be said) of the wizard Joseph Harries in a local amateur production. How I enjoyed the power that gave me! So, folks, I can make you well. Those who go through life afflicted by this miserable bluestone curse should really undertake a long course of therapy, but for a start I can promise you that if you sing "I believe in glaciers" five times, at the top of your voice, next time you put an ice cube into your whisky glass, you will feel much better. They tell me that whisky has miraculous restorative powers. Preferably Welsh whisky. That will not actually heal you entirely, but it will be the beginning of a long (and maybe painful) route back towards sanity. If your affliction is so severe that you believe in healing stones, sacred springs, and spotted dolerite fairies, the healing process will take longer -- but you must persist with the treatment, for the good of your family. You know it makes sense.

Stonehenge and the Curse of the Bluestones

The Curse of Merlin the Wizard

Ed has raised an interesting issue by asking exactly how we should define the word "bluestone." Well, here's the best definition I can come up with: "A bluestone is a piece of rock, of any size, found in the environs of Stonehenge, which supports the theory of long-distance haulage by Neolithic tribesmen from sources in West Wales." Will that do? There's no point in talking about lithology, or colour, or size, or detailed provenance, or anything else remotely scientific, because every other definition falls down because of "exceptions to the rule."

Traditionally, stones that do not fit that definition (such as those sandstones and limestones that have come from other parts of Wiltshire or Somerset) are simply not referred to as "bluestones."

Since HH Thomas originally came up with his thesis that the bluestones were from the Carn Meini area in Mynydd Preseli, Pembs, the human transport theory has been a blessing for the archaeology establishment, for studies of prehistory, for the English tourist trade, and in many other fields of noble human endeavour. Thomas pushed the idea hard, Atkinson pushed it even harder, and it has been accepted -- virtually without question -- as THE TRUTH ever since. Learned professors have made their academic careers on it, and it has turned some of them into media stars as well. And without the story, Stonehenge would never have become the icon that we all know and love, and the prospects for the Wiltshire tourist trade would be dismal indeed. "So, dear friends," they all say, "we are greatly blessed, in multifarious ways, by this delightful tale of our heroic ancestors. Let us therefore keep it going, with ever more imaginative expositions and elaborations....."

But how much of a BLESSING is it? I have a theory that it is actually a CURSE. When you come to think of it, it has turned thousands -- if not millions -- of normally rational and well-educated human beings into whimsical fantasists, pondering endlessly on boat design, rollers and levers, friction and lubrication, man-hours and logistics and so forth -- when they would all have been better occupied in solving the problems of inequality and hunger. It has turned archaeology into a hugely popular subject which thinks of itself as scientific but which is increasingly fanciful, searching obsessively for rituals, reasons and sacred motivations before sorting out the facts of the matter in hand. Shall we mention the words "vanity", "power" and "control"?? Some learned professors have become so obsessed with healing stones and sacred springs that they see evidence where there is none, and are accused by some of their own kind of being "out with the fairies." Others, suffering under the same curse, have become intolerant of dissent to the point of being mean and vindictive -- just look at the vitriol poured on poor Geoffrey Kellaway for daring to say inconvenient things about bluestone transport. So it is a curse, visited initially upon HH Thomas, then upon Richard Atkinson, and then upon generation after generation of archaeologists, media people, tourist operators, school teachers and even university lecturers.

Personally, I blame Merlin. I am immune from the curse, because (like Merlin) I was born in Carmarthen, and because I have spent so much time wandering around Carn Meini that its evil power no longer affects me.

The Local Geology

These are nice simple and yet informative short descriptions (from Natural England) of the local geology in Wilts, Somerset and the Bristol and Bath area:

Wiltshire: http://www.naturalengland.org.uk/ourwork/conservation/geodiversity/englands/counties/area_ID39.aspx

Somerset: http://www.naturalengland.org.uk/ourwork/conservation/geodiversity/englands/counties/area_ID30.aspx

N Somerset, Bristol and Bath: http://www.naturalengland.org.uk/ourwork/conservation/geodiversity/englands/counties/area_ID31.aspx

Thoroughly recommended.

Stonehenge: Local Bluestones from the west

I am far from being an expert on the geology of Somerset and Wilts, but on looking at the geology maps I am encouraged to do a bit of speculation. Let's refer to everything at Stonehenge that is not sarsen stone as BLUESTONE, since that's what people have been doing for years. There are hundreds if not thousands of bluestones of all shapes and sizes at Stonehenge that could well have come from the west and north-west, within 80 km of Stonehenge, and which could well have been carried by ice, if it did indeed come in from the Bristol Channel in the direction(s) discussed in earlier posts. So which "local" rock types might we expect to be represented in the Stonehenge bluestone assemblage? Look at the map and key above.

For a start, we might expect erratics of Upper Greensand, Corallian, Portland beds (Upper Oolite), Middle and Lowe Oolite beds (including some limestones and some sandstones), Upper Triassic beds (marls, sandstones, conglomerates), Carboniferous Limestone (from the Mendips) and even Coal Measures (mostly sandstones and shales, with interspersed coal-bearing beds). There are also a few outcrops of Old Red Sandstone on the flanks of the Mendips, to the west of Bristol and along the North Devon Coast -- and a few small exposures of igneous rocks too. I have forgotten here about the clay beds, on the assumption that they would not have contributed large blocks and monoliths to an erratic load or a till cover (they would have been broken down for the most part into silt and clay fractions). In short, sandstones, gritstones, and limestones galore COULD have been entrained, transported and finally dumped by overriding ice from the west.

There are lots of all of these rocks at Stonehenge, but archaeologists have tended to assume (a) that they have been imported manually by the Stonehenge builders, and (b) that they have therefore come from quite close at hand -- ie from the Vale of Wardour or from the Eocene outcrops to the south of Salisbury Plain's chalk downlands.

Here is a question for the geologists: Have any of these "local bluestones" found at Stonehenge been definitely fixed to the rock outcrops to the south or south-west of Stonehenge, or could they equally well have come from the west or north-west? Chilmark, in the Vale of Wardour, is often mentioned as an Upper Greensand source for "Chilmark stone" -- but is that just wishful thinking on the part of geologists and archaeologists who had no great desire to look for sources further afield, or in another direction?

Where did the Packing Stones and Mauls come from?

On the left, typical packing stone debris and rubble -- this sort of material has been found, in vast quantities, during every excavation. Some of the stones are far too large to have been used as hammer-stones or mauls -- and this is a fair question: would this material have been carried from "quarries" many kilometres away, just to have been used as packing stones? Unlikely, in my view......

Following on from my last post, here is an extract from Chapter 6 of my book:

Almost every stone -- whether sarsen or bluestone -- that was pulled and pushed into a vertical position at Stonehenge was stabilised with packing stones and chalk rubble often containing flints. There is a phenomenal amount of this “clutter” at Stonehenge, and as far as we can see it has never been systematically analysed. An examination of Richard Atkinson’s photo archive from the 1958 excavations is very revealing; photo after photo shows rounded and sub-angular stones packed around the monoliths, sometimes with bits of antler thrown in for good measure. Some of the stones are as big as a human skull. The heaviest one found thus far weighed 30 kg, but Richard Atkinson thought that some mauls were as heavy as 60 kg when in use. (How would you actually use a maul which was that heavy?) Christopher Green refers to “chips and fragments of almost all the rock types that have been identified in the structure” -- including sarsen and bluestone. He says that in the course of 22 excavations at Stonehenge over 11,500 stone fragments have been recorded; some of this material is packed into stone holes as a sort of matrix between bigger stones, but many other fragments simply littered the ground surface in the past, prior to being incorporated into the soil horizon by earthworm activity and so forth.

In the excavations of Gowland and Hawley early in the twentieth century, they recorded 447 mauls and hammerstones, mostly in pit fillings, which had been used for the shaping of the sarsens. The tooling marks on the surface of the great monoliths are still visible. Some of the tools were made of a very hard type of sarsen which is densely cemented by microcrystalline silica, and which was therefore a tough and resistant tool. Other packing materials are more intriguing, since they are made (according to William Hawley) of Jurassic oolitic ragstone and glauconitic sandstone. Rock of the former type was supposed to have come from near Chilmark, around 20 km to the south-west of Stonehenge, in the Vale of Wardour. The latter was supposed to have come from the Upper Greensand beds in the same area. Dr Green thinks that these stones were collected there and carried to Stonehenge in a separate “stone collection” exercise. However, that is a matter of debate, and nobody has seriously questioned Hawley’s suggested provenances for the stones. These rock types also outcrop to the west, in the western part of Wiltshire and in Somerset, and Geoffrey Kellaway pointed out in 1971 that they could have reached the Stonehenge area as glacial erratics. The Upper Greensand outcrops around Warminster, about 22 km to the west -- not far, as it happens, from the site of Boles Barrow. Also, it is doubtful that these two stone types would have had any value as hammerstones, since they are generally too soft and only become hard when impregnated with calcium carbonate, for example by being placed in a chalk pit. Would piles of these soft sandstone and limestone rocks have been fetched all the way from the Vale of Wardour just to be used for stabilising standing stones in their sockets? That seems very doubtful to me.

The Great Erratic Hunt

Wiltshire geology map and cross-section. Courtesy Wilts Geology Group. With a bit of luck, if you click on either image you should get an enlargement on your screen. If there are Jurassic or Lower Cretaceous erratics in the vicinity of Stonehenge, my theory is that they should have come from the west or north-west.

If glacier ice approached Stonehenge from the west, how far eastwards did it extend? One theory that I have put forward with Lionel Jackson (in EARTH magazine) is that the ice actually came quite close to Stonehenge, with a line of "bluestone" boulders extending eastwards from the Chalk Escarpment across the gently undulating chalk downs -- marking the position of the junction between Welsh ice (on the north side of the junction) and Irish Sea ice (on the south side). We argued that this line or "train" of erratics, like the Foothills Erratic Train in North America, would have been quite easy to follow -- and would have been known to the Neolithic tribes inhabiting the chalk downs. So they collected them up for their building project, at first close to Stonehenge and then successively further and further away, until either the stone supply ran out or they ran out of energy. I still think that is a reasonable theory, in terms of glacial theory -- especially if we think in terms of the modelled ice extent described in earlier posts on this blog.

But how likely is it that the stone collectors will have collected ALL of these erratics? Would there not have been some, deeply embedded in the ground, or maybe hidden in thick copses of trees or undergrowth, that they will have missed? Quite so -- I freely admit that it would be good to find some more erratics still in position to the west of Stonehenge. Well, we have Boles Barrow bluestone boulder, for a start -- but that was a "collected boulder" too -- and not in its original position.

Are we too preoccupied with spotted dolerite? I wonder what other stones there might be on the Plain, or in buildings or stone walls, to the west of Stonehenge? And maybe we should think much more about erratics derived from the rocks which outcrop to the west -- for example the limestones and sandstones of west Wiltshire, Somerset and the Mendip area?

Stonehenge -- lessons from Avebury

Avebury and Stonehenge -- two of a kind? Both manufactured from a convenient litter?

Came across this from a chapter in a book on the Marlborough Downs:

"The origin of the stones in the Avebury stone circles is often considered to derive from one of the accumulations that still exist on Overton or Fyfield Downs to the east of the site, each stone being dragged a distance of several kilometres up and over Hackpen Hill. Such suggestions are merely a response to where boulders can be found in abundance today. However, as noted above stone was certainly available locally and may have been present on the site itself. There is no reason for the stones to have been hauled such a distance. Local accumulations of sarsen are or were certainly present here and it is likely that the valleys were once covered with boulders even though only isolated examples now survive. The farmer of land east of the West Kennet Avenue confirmed that a ridge c1.0m high and 30m wide `consists of a seam of sarsen that runs through the field' (Barker 1985, 21). Thus the land for this massive construction would need to be cleared first and any boulders within the immediate vicinity removed. Given this scenario the stones for the circle may well have come from the immediate vicinity of the henge, some potentially from the interior."

(Ch 8. Some observations on perception, consolidation and change in a land of stones.
David Field)

I think that's rather interesting -- confirming what many other archaeologists and geologists have said about Neolithic people being opportunists and scavengers, rather that highly organized long-distance stone hauliers. It makes a great deal of sense to assume that both at Avebury and Stonehenge the builders simply used what was on the spot, and cleared a litter of large stones from the landscape. As I have said elsewhere, after they had used up all the stones in the immediate vicinity, they cast about further and further afield, until they finally ran out of stones, ran out of energy, or got bored. Was either monument (Avebury and Stonehenge) actually FINISHED? I doubt it.

Silbury Hill -- one bluestone, or two?

Just a reminder -- this is Pete Glastonbury's photo of the Silbury Hill bluestone at the AK Museum in Avebury. it's very small -- just the size of a thumbnail -- so we should call it a flake or a fragment rather than a stone or a boulder!

Rumour has it that there is a bit of a spat blowing up over the lithology and provenance of the one (or two?) pieces of "bluestone" found on Silbury Hill by our old friend Richard Atkinson. Are they really fragments of spotted dolerite like those found at Stonehenge? Or are they hornblende schist? Watch this space......

Gravels, pebbles and Bluestones

Near the confluence of the Nadder and Avon -- the river terraces in this area were examined by Chris Green

One of the main reasons for scepticism about glacier ice reaching as far east as Salisbury Plain is the scepticism of geomorphologists Jim Scourse and Chris Green. Both of them are utterly convinced that the ice of the Irish Sea Glacier never got this far -- and they expound their reasons in the big "Science and Stonehenge" book published in 1997. Jim uses a glaciological argument (which I will examine on another occasion) and Chris uses the evidence of pebbles in terrace gravels to demonstrate that there is no "foreign" material in the river catchments of the chalk downland.

Now I have great respect for Chris (he and I were contemporaries in Oxford) but I do wonder how sound his evidence actually is. I have looked again at the "Nature" article which he published in 1973 which purported to show a "complete lack of glacially derived material in the Pleistocene river gravels of the Wylye, Nadder and Avon" -- and I wonder how he can come to that conclusion. He concludes that there is less than 1% of far-travelled material in the area around the confluences of the three rivers, and downstream from there in the Avon valley. He claims to have analysed 50,000 pebbles, but leaving aside the difficulty of actually spotting pebbles of far-travelled sandstone, dolerite or rhyolite in around 30 washed samples of terrace gravels, he seems to have used vein quartz as the key indicator of "foreign rock presence." Now that in my estimation is a rather dubious thing to do -- and I assume that vein quartz was used because it is white, and is easy to spot quickly. He seems to assume that if there are no vein quartz pebbles present, there are no other foreign rocks either. He also refers to small numbers of pebbles of quartzites, grits and cherts, and says that these could have all come from "nearby Tertiary formations." That is true, but they COULD also have come from much further away, to the west! Those rocks occur in very low percentages (generally far less than 1%) and from many samples they are entirely absent.

Chris's work leaves us with many questions, for example relating to his ability to spot far-travelled pebbles, to the use of vein quartz as a key indicator, and to the clustering of the sampled terrace sites around Salisbury and downstream from there in the Avon Valley. We also need to highlight the fact that far-travelled materials are now popping up all over the place on Salisbury Plain -- as indicated in Chapter 6 of my book. The number of sources for these pebbles and flakes must now be approaching 30 -- and while some may be fragments of broken or shaped bluestone monoliths, we should remember that Atkinson and others have referred to the fact that most of those at Stonehenge are "undressed" or in their original states. What percentage of the total stone population on the interfluves is "foreign" and from the west? Is it higher, or lower, than the percentage of foreign stones in the river terraces? We won't know the answer to those questions until a lot more work is done.

Chris does NOT address the problem of the foreign stones which have been found, ever since excavations began, in the neolithic and Bronze Age sites dotted about on Salisbury Plain. Nor does he examine the pebbles present in the river banks of the middle and upper reaches of the three rivers in question.

Finally, I would dispute Chris's contention that the apparent (more apparent than real?) lack of far-travelled pebbles in the terrace gravels disposes, once and for all, of the idea that glacier ice once reached Salisbury Plain. It does nothing of the sort. Most of the material in glacial deposits is rather local, and in many of the tills and outwash deposits I have seen, really far-travelled materials are quite rare. As I have mentioned in other posts, if an ice margin is cold-based, there may be virtually no meltwater production and virtually no deposits to show which areas were ice covered and which were not.

We know that there are quite high percentages of foreign stones in the Thames terraces around Reading (up to 30% in some cases), and as Chris indicates, these are good indicators of the presence of glacier ice from the north during the "Anglian" and "Wolstonian" glaciations. Many of the foreign pebbles in the Thames terraces appear to have come from a deposit called "the Northern Drift" -- assumed by many to be an ancient till deposit. Can we -- and should we -- draw close parallels between the Thames Basin and Salisbury Plain? How similar were the glacial and non-glacial conditions around Reading and around Amesbury? How did the Downland rivers behave during the colder episodes of the Ice Age? Since they are flowing -- at least in part -- on chalk, was their flow continuous or intermittent? If it was intermittent, what effect did this have on pebble transport and terrace construction?

This is an interesting dilemma, worthy of more discussion and more field research..... and in the meantime I'll stick with my belief that the ice DID reach Salisbury Plain on at least one occasion. That belief is supported by the abundant erratics that we all know about on the chalklands, and by the presence of affirmed glacial deposits to the west and north-west of Salisbury Plain.