Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Tuesday, 29 December 2009

The great Millennium Stone Pull

Came across this picture in my photo album -- which reminded me just how idiotic this whole theory about the human transport of the stones actually is. If HH Thomas had not dreamt up the whole silly notion, just think what a lot of human effort might have been spared -- millions of words in print, endless debates on blogs and forums, vast sums spent on reconstruction projects, and the same old stuff going round and round, with people in general fascinated by the idea of ancient tribesmen invested with extraordinary engineering skills, stupendous imagination, and incredible social and economic motivation -- not to mention the navigational and maritime skills used in treacherous coastal waters with high tidal ranges, mudflats, storm waves and roaring currents.

I thought for a long time that it was a fine thing to engage in some of the Stonehenge blogs, on the basis that discussion would lead all of us eventually to the truth........ but no matter how one attempts to address the real issues of engineering and motivation, and no matter how much one tries to debate the glacial ("alternative") theory, people will insist on going right back to square one and asking "I wonder how they did it?" and coming up with endless theories, apparently without ever stopping to ask the questions "Did they do it?" and "Is it necessary to speculate on this anyway?"

The picture above shows how difficult it was to control one smallish bluestone on a sledge, on a moderate slope, during the "Millennium Stone" pull in the year 2000. With the aid of netlon (low-friction netting), modern ropes, asphalt roadways and help from cranes, JCBs and modern boats, the project was still a shambles that left the stone on the bed of Milford Haven.

Here's a proposal -- forget about the human transport altogether. Pretend that the daft idea had never even been thought of. And concentrate all the formidable brain power of the people of the planet (well, a little bit of it anyway) on solving the riddle of how natural processes carried some of the Stonehenge "bluestones" from West Wales to Somerset and Wiltshire. Jim Scourse and Chris Green have declared -- in print -- that it was "impossible" for natural processes to have been responsible for this entrainment and transport. Not a word one should use lightly........

Friday, 25 December 2009

Those undistinguished outcrops

Carn Llwyd, not far from the coast and above the town of Newport. This little outcrop is so insignificant that if you are a few hundred metres away you hardly notice it at all. It is well down the slope on the northern flank of Carningli.

Happy Christmas everybody!! Escaping from the grandchildren for a few minutes, while the turkey cooks to a turn, I retired to the sanctuary of my study and pondered on undistinguished outcrops. It's worth flagging up again just how significant the new findings from Rob Ixer and Richard Bevins are. The new discoveries from the source area of many of the Stonehenge bluestones suggests not only that the stones were not preselected by rock type (ie nobody went out hunting for spotted dolerite) but that they were also not preselected from prominent outcrops. The idea that the stones were taken from Carn Meini (a) because the crags were made of the mystical or magical spotted dolerite which reminded the gatherers of the night sky, or which had healing properties; and (b) because the crags were prominent on the skyline, and were therefore treated with awe or invested with great significance, is now shown more than ever to be pure fantasy. The stones are not just made up of many different lithologies (some of which, like volcanic ashes, are soft and crumbly) but they also come from some places which are not at all prominent in the landscape. Examples of such source areas are Carn Clust-y-ci and Carn Llwyd near Newport, and Pont Saeson near Brynberian. At the latter place there are no prominent rock outcrops at all -- just some exposures of bedrock on the flanks of a wide river valley.

Unless anybody can dream up some wildly wacky reason for stones to be gathered up from such a place and dragged all the way to Stonehenge, we might as well dispense with the human transport theory once and for all, and concentrate on the REAL problems -- ie

(1) what were the glaciological conditions responsible for the entrainment, transport and dumping of the stones?

(2) exactly when did this happen? and

(3) where were the stones dumped, and how far did they need to be carried from their "discovery points" to the Stonehenge monument?


Key source of info:
British Archaeology
Important revision to Stonehenge bluestone theory

In the News pages of the Nov/Dec 2009 issue of British Archaeology, it is reported that new petrographical work by Rob Ixer (University of Leicester, Department of Geology) and Richard Bevins (National Museum of Wales) had suggested that some of the Stonehenge bluestones had not come from Pembrokeshire, but (in Ixer's words) from "a far wider and, as yet, unrecognised area or more likely areas". As the magazine was being printed, however, Bevins was out in the field, and found an apparent source for the rocks in question north of the Preselis. Ixer and Bevins have kindly written this interim note on this latest development.

Stilpnomelane-bearing rhyolites/rhyolitic tuffs at Stonehenge are most probably from the Preseli Hills region.
by Rob Ixer & Richard Bevins

" from undistinguished outcrops in the low ground north of Mynydd Preseli, close to Pont Saeson".
"...... but a search for their associated source rocks must no longer be restricted to the prominent outcrops on the Preseli Hills."

Wednesday, 23 December 2009

Stonehenge and the Olympics

Now that considerable doubt has been thrown on the "authorized" version of the Stonehenge story -- and especially the bluestone chapter -- I wonder how much of that story will be modified on English Heritage web sites and publicity material? I suspect that the fairy tales about Neolithic tribesmen and their heroic efforts (not to mention their amazing navigational skills) in transporting the bluestones from A to B are actually too valuable to ditch, especially with the London Olympics not very far away. Stonehenge, great national treasure that it is, will be marketed for all it's worth, and the more heroic tribesmen figure in the story, the better the foreign visitors will be pleased, and the the more foreign exchange will jangle into the EH cash-boxes. They will have been charged by the Government with maximising their income during and around the Olympics, so that public funding can gradually be pulled, and I predict that they will do virtually nothing to jeopardise their chances of doing that, by "watering down" the authorized story of expressing doubts about the truth of any of it........

I will have a look at some of the current EH material, and report back.......

Friday, 18 December 2009

Glaciation of the Mendips

The Mendips -- glaciated or not?

I've always been intrigued that many geologists and geomorphologists have argued that the Mendips have never been glaciated. For some reason they want to maintain the pretence that ice coming in from the Bristol Channel skidded to a halt just a few kilometres inland from the present coast, somewhere around Court Hill. The main inland sites with good evidence of glacial deposits are Kennpier, Nightingale Valley, Weston-in-Gordano, and Yew Tree Farm, none of which is more than 5 km from the coast. These deposits are variable, and include flow tills and fluvioglacial gravels. So nobody can doubt that this area was glaciated by ice coming in from the west.

But then things get a bit silly. Because these deposits indicate ice-edge or ice-marginal conditions, some quite senior geomorphologists have argued that they show us the maximum inland extent of the ice. There is nothing to suggest that this was a true TERMINAL MORAINE, and indeed we know that the ice DID extend much further inland on at least one occasion. There are clear traces of glaciation at Bath University / Bathampton Down, Hampton Rocks Cutting, Newton St Loe, and Stidham Farm on the River Avon. So the ice extended at least 35 km to the east of Kennpier, Court Hill and the other sites mentioned above. Much of the Avon Valley must have been glaciated. To the south of the Mendips, the ice reached at least as far inland as Greylake. Maybe there were two lobes of ice, one pushing up the Avon Valley and the other pushing in from Bridgwater Bay into the Somerset Levels. But it is almost inevitable, given this scenario, that the Mendips were also glaciated; and indeed the deep gorges of the Mendips speak of huge volumes of glacial meltwater carving into the Carboniferous Limestone bedrock. Some authors have argued that the gorges were cut by water from snowmelt under periglacial conditions, but I just do not think that snowpatches, even over many thousands of years, could have provided the water volumes necessary. We need a full ice cover across the Mendips -- and that is indeed what the glacial modelling suggests.

Bluestone monoliths

Callum and Finley -- bluestone monolith in Tycanol Wood, Pembs

Bluestone monoliths or orthostats cause great excitement in Wiltshire, but they are all over the place in Pembrokeshire. This one is on the north side of the Preseli Hills, and is made (like many others in the area) of bluish dolerite. Probably it is local, from the Fishguard Volcanic series of rocks. Such rocks have been used since the Neolithic, usually very close to their places of origin, for cromlechs, standing stones, lintels and window sills, headstones for graves, and (as here) as gateposts. It is virtually impossible to say which of these stones are prehistoric and which are modern -- the collection and use of the stones goes on to this day.........

And forget about the idea that there was a "bluestone quarry" -- stones have been collected from the litter or scatter of elongated stones right across the North Pembrokeshire landscape. The collectors -- now as in the Neolithic -- have been opportunists and pragmatists driven by utilitarian motives rather than sacred or ritual ones.

Monday, 7 December 2009

Clay-with-flints and Chalky till

Back to the UK. Been pondering on the ancient deposits that sit on the chalk in Eastern England. The map shows that in Hertfordshire there is a south-western zone with "clay-with-flints" (brown) on the interfluves (implying that these deposits are very old, and are indeed older than many of the river valleys) and a north-eastern zone (light blue) with Chalky Till. This is a greyish colour (see the photo above) and contains chalk, flint, and erratics from the north. It has all the characteristics of a typical till laid down by a wet-based glacier -- supposedly in the Anglian Glaciation. Does the distribution of this till actually give us the extent of the maximum glaciation in this area?

OK -- on to the "clay-with-flints" (which occurs quite frequently on Salisbury Plain and on the higher Chalk Downs. Here is the Wikipedia entry:

Clay-with-Flints was the name given by W. Whitaker in 1861 to a peculiar deposit of stiff red, brown or yellow clay containing unworn whole flints as well as angular shattered fragments, also with a variable admixture of rounded flint, quartz, quartzite
and other pebbles. It occurs in sheets or patches of various sizes over a large area
on the north to Sussex on the south, and from Kent on the east to Devon
on the west. It almost always lies on the surface of the Upper Chalk, but in Dorset
it passes on to the Middle and Lower Chalk, and in Devon it is found on the Chert-Beds of the Selbornian group (A. J. Jukes-Browne, The Clay-with-Flints, its Origin and Distribution, Q.J.G.S., vol. lxii., 1906, p. 132).

Many geologists have supposed, and some still hold, that the Clay-with-Flints is the residue left by the slow solution and disintegration of the Chalk by the processes of weathering; on the other hand, it has long been known that the deposit very frequently contains materials foreign to the Chalk, derived either from the Tertiary rocks or from overlying drift. There is evidence against the view that the deposit is mainly a Chalk residue, This shows that many patches of the Clay-with-Flints lie upon the same plane and may be directly associated with Reading Beds. He concludes that the material of the Clay-with-Flints has been chiefly and almost entirely derived from Eocene
clay, with addition of some flints from the Chalk; that its presence is an indication of the previous existence of Lower Eocene Beds on the same site and nearly, at the same relative level, and, consequently, that comparatively little Chalk has been removed from beneath it. Finally, I think that the tracts of Clay-with-Flints have been much more extensive than they are now. Clay-with-flint is a nutrient rich substance unlike chalk.(bc. cit. p. 159).

It is noteworthy that the Clay-with-Flints is developed over an area which is just beyond the limits of the ice sheets of the Glacial epoch, and the peculiar conditions of late Pliocene and Pleistocene times; involving heavy rain, snow
and frost, may have had much to do with the mingling of the Tertiary and Chalky material. Besides the occurrence in surface patches, Clay-with-Flints is very commonly to be observed descending in pipes often to a considerable depth into the Chalk; here, if anywhere, the residual chalk portion of the deposit should be found, and it is surmised that a thin layer of very dark clay with darkly stained flints, which appears in contact with the sides and bottom of the pipe, may represent all there is of insoluble residue.

A somewhat similar deposit, a congbomirat de silex or argile a silex, occurs at the Paris basin, in the neighborhood of Chartres, Thimerais and Sancerrois.

So what are the relationships of these two deposits? Both are highly variable -- and the Clay-with-Flints has -- in some instances -- been interpreted as a glacial deposit because it contains so much erratic material. Mostly, however, it is interpreted as a residue or remnant of younger (Tertiary) rocks that once capped the Chalk and which have subsequently been eroded away.

More on erratic trains

Some of the boulders in the erratic train are 16m in diamater.

Thanks to Lionel Jackson for bringing this to my attention. There are more examples here of "erratic trains" -- this time strung out in the lowlands of Tierra del Fuego, and traceable back into the mountains of the Cordillera Darwin. The thousands of boulders in the erratic trains are largely unmodified by glacial abrasion, and they sit on top of moraines -- so they are interpreted, like the Foothills Erratic Train in North America, as having come from valley side avalanches descending onto moving glacier ice. The ice has carried them away on the glacier surface and has "attenuated" or strung them out -- so that what might have been a cluster to start with has been transformed into a linear feature. Interesting info, which might help us in our attempts to work out what the glacier dynamics were when the erratics were transported from Wales to the eastern side of the Bristol Channel.

Enigmatic boulder trains, supraglacial rock avalanches, and the origin of “Darwin’s boulders,” Tierra del Fuego
by Edward Evenson et al
GSA Today, v. 19, no. 12,pp 4-10

Sunday, 6 December 2009

Finding the GBG ice edge

The two maps above show ice movements during earlier glaciation(s) of eastern England, with "British" ice from the north pressured eastwards by Scandinavian Ice coming in from where we now have the North Sea (which was not there at the time). Note that the ice edge is almost as far south as London.

These two UK maps are of limited use, since they relate to the Last Glaciation. There is now great dispute as to where the southernmost Devensian ice limit might have been, following the discovery that till on the Scilly Islands is of this age. (Thanks to Clark, Gibbard and Rose)

Lessons from Jameson Land?

Jameson Land, East Greenland. On the satellite image, Jameson Land is the large unglaciated area to the east of the broad Scoresby Sund -- which carried the ice from a number of the East Greenland Fjords. The undulating landscape of central Jameson Land is very different from that of the "fjordland" to the west and north.

Ah - happy days! I walked across part of this area and worked here in 1962. Been pondering a bit on how we might find parallels between this area and Salisbury Plain -- a lot of geomorphology is done by analogy, in which we seek guidance to what happened in one landscape by reference to what can be observed elsewhere, in similar terrain or where glaciological circumstances might have been similar.

Jameson Land might give us clues -- because instead of seeing evidence here of streaming ice and deep erosion, we appear to have a landscape which has been effectively protected by stagnant or sluggish cold-based ice. Lena Hakansson, who has studied this area, says that: "... local ice with limited erosion potential covered and shielded large areas for substantial periods of the last glacial cycle." Local ice -- that's interesting, and maybe something that gives us a guide to what might have happened over the Mendips, Dartmoor and Exmoor. But there are erratics and some exposures of till in Jameson Land -- these appear to be much older.

There are plenty of erratics on Salisbury Plain, as shown in earlier posts on this blog. Till is usually observed in river cuttings or road excavations. But because Salisbury Plain is made of chalk, the effects of fluvial erosion are very limited. What we have are coombes or dry valleys, but few exposures or cuttings to tell us whether there are any thick sediments present, and how they may be distributed. We know about the "clay-with-flints" and occasional river terraces made of gravels, but otherwise there appear to be no records of anything that might be referred to as unequivocal "till" or boulder clay. I wonder what's lurking beneath the surface, waiting to be discovered?

Friday, 4 December 2009

Glaciation "impossible" on the Wiltshire Downs?

Crusoe Glacier, Axel Heiberg Island, N Canada. I visited this glacier more than 40 years ago -- very impressive, with relatively clean ice, and in places a vertical ice cliff simply sitting on the tundra (which of course is permanently frozen).

I have been looking again, in the big Cunliffe/Renfrew "Science and Stonehenge" book (1997), at the chapters written by Jim Scourse and Chris Green. I am still amazed, as I was when I first read them. Seldom have I encountered such certainty, and without accusing them of pandering to the wishes of their sponsors and most influential readers (ie the archaeology establishment) I wonder why and how they can have brought themselves to the point of using the word "impossible" with respect to the glaciation of Salisbury Plain, or even a part of it. These chapters, which we might call "the Gospels according to St James and St Christopher", have of course been heavily cited by the likes of Darvill, Wainwright, Parker-Pearson and Pitts -- who say, repeatedly, that if "their experts" tell them that glaciation this far east was impossible, then it WAS impossible. My two learned friends are frequently referred to as either geologists or glaciologists -- they are neither, since (like me) they are geomorphologists. Their opinions are no more reliable than mine...........

What I find intriguing -- and somewhat irritating -- is the manner in which they waste a great deal of time going after some of the extreme and peripheral issues raised in the writings of Geoff Kellaway -- and spend very little time addressing the key issues:

1. Why is there no evidence in support of the human transport hypothesis?
2. Why are there so many rock-types represented at Stonehenge, and so many variations in "bluestone" size and shape, varying from substantial monoliths down to small stones and fragments?
3. If you are looking for "evidence of glaciation" as a geomorphologist, surely it is there, before your very eyes, in this complex and varied assemblage of "foreign stones"?
4. If the ice of the Irish Sea Glacier did (as they admit) extend across the Bristol Channel coast and into Somerset, would it not be more logical to assume that the "foreign" stones at Stonehenge (and elsewhere) were erratics, dumped somewhere to the west of Stonehenge?

They seem to have major problems on these points, and they do not address them properly. I'm not saying they are wrong in everything they say -- but I do challenge some of their assumptions. They say that if the Plain was glaciated, there should be glacial sediment sequences and "depositional landforms." I disagree. They say that if the chalk scarp had been overridden by ice from the west, there would be "glacio-tectonic structures." I disagree. They say that glaciological theory makes it impossible for glacier ice to have carried erratics from Preseli to Stonehenge. I disagree. They say there is an inconsistency between "observational and theoretical data.... and the regional geological data." I disagree.

The answer, when it comes (and it will come) will be partly down to the collection of field data and partly down to a better understanding of what happens on a chalk downland when it is affected by cold-based dry ice. It is patently obvious that Salisbury Plain was not affected by warm-based and "wet" ice carrying huge amounts of debris; if it had been, there would be glacial sediment sequences, moraines and other features all over the place. But I prefer to look, for my parallels or analogies, at the northern parts of Canada, the Dry Valleys of Antarctica, and maybe parts of North Greenland, where polar-based ice affected the landscape without doing very much to it at all. This is where our debate should concentrate...... and all contributions will be gratefully received!

Hobgoblin musings

This simple map shows the locations of the bluestones and the sarsens on the site today. Missing stones everywhere -- if they were ever there in the first place.....

On another blog site, a fellow who calls himself "Hobgoblin" has been examining the implications of the latest geology findings by Rob Ixer and Richard Bevins. This is the site:

And this is his commentary:

"So where does this leave the bluestone transportation debate?

The Stonehenge sarsens, the largest used in the Great Trilithon estimated at 50 tons, were brought 25 miles from the Marlborough Downs, which was a significant achievement in its own right. Transporting 4 ton bluestones 160 miles by human effort from South Wales to Salisbury Plain certainly seems plausible. There were also a small number of limestone blocks and slabs used in the construction of Stonehenge brought to the site for the specific purpose of packing material to support the much larger sarsen uprights. The limestone quarries have been identified as Chilmark, 12 miles west, and 3 miles southeast at Hurdcot.

The number of different rock types found amongst the bluestone group at Stonehenge is cited as significant evidence of glacial deposits, with debate continuing for the location of the exact quarry sites seen as the basic flaw in the argument for human movement of the bluestones, in other words identifying the quarry site(s) will prove the human agency method. According to Ixer & Bevins's revision statement were are still looking at Preseli as the geological provenance for the majority of bluestone. Anyone familiar with the Preseli mountains will be aware that there is ample loose bluestone over a number of peaks in the mountain range and would therefore not need to be quarried but pieces the appropriate size simply collected with minimal effort for use in the monument requiring later minimal dressing prior to erection. The bluestone constructions at Stonehenge were built and rebuilt maybe as many as five times over a 400 year period. We do not know if all the bluestones were brought at the same time, but it is quite conceivable that different working parties, possibly generations apart, collected from different sites in the Preseli mountains. As Rob Ixer told BA, had “different groups [of people] brought different stones?”

As Anthony Johnson states in his recent work on Stonehenge:

“ there appear to be so relatively few bluestone finds outside Stonehenge and its immediate environs, with no extensive distribution across the Plain or its river valleys, a glacial derivation is considered unlikely. The glaciation theory has to address why the people building the earliest stone monument appear to have selected only exotic stones; if Salisbury Plain had been littered with a variety of rocks, including local sarsen, was the intention to gather material suitable to build the first stone circle, or primarily an exercise in prehistoric field geology?

It is far easier to envisage the bluestones collected at the source (i.e. where they outcrop), than to see them as having been selectively chosen from the surrounding landscape. There is a another important point to consider here: whilst a variety of large exotic rocks and even hammer-stones and mauls was used in the packing of the sarsen uprights, implying that stone for this purpose was in short supply, none was bluestone; had it been generally present within a local glacial assemblage it would undoubtedly have been collected and utilised.” [1]

It would appear the building materials for Stonehenge were carefully selected from various sources for specific purposes, far from being a “rag bag mix of glacial erratics”.

With all due respect, Mr Hobgoblin, I think I have to part company with you on a great deal of that. Some people may think the sarsens were transported 25 miles from the Marlborough Downs, but I certainly don't, and nobody has ever produced evidence in support of that theory. Pure speculation. And to use that as a basis for saying "Well, if they could do that, then moving little bluestone blocks from Wales would have been easy" is to get into circular reasoning territory. To say that the Preseli area was littered with blocks which could be "simply collected with minimal effort for use in the monument" is sheer fantasy. You are talking about incredibly rough terrain, dense woodland, bogs, steep slopes, and fast-flowing streams -- this terrain was vastly different from the gentle grasslands of Salisbury Plain. And I disagree with Anthony Johnson -- there is no evidence that the builders of the earliest stone settings at Stonehenge only used "exotic" stones (bluestones). We do not know that. At least two of the bluestones were sandstones -- left as stumps now under the turf. We only have traces of 43 "exotic" bluestones. Those who want there to have been 80 or more have to explain where all the others are -- I have argued in my book that they may not have been there -- ever. Even if they were present at one time, it is likely that they were small sarsens, maybe later removed and incorporated into later stone settings, or used as lintels in the sarsen circle or on the trilithons.