THE BOOK
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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Monday, 28 March 2011

Salon is increasingly unfashionable

Here is the latest from Salon -- based on those press releases of a few weeks ago relating to the zircon research and the identification of the bluestone source at Pont Saeson.

Quote:  "The finding has implications for the route by which the stones were transported to Stonehenge. Previous theories have suggested an arduous overland haul south from the peaks of Mynydd Preseli to Milford Haven, and then by sea and river to Salisbury Plain. These new outcrops are only a short distance (c 5km) from the harbour at Newport: the overland journey would have been much shorter, but the voyage via the Irish Sea is considerably longer and potentially more hazardous."

In deference to "our Fellows Geoff Wainwright and Tim Darvill", whoever wrote this appears to be incapable of accepting that the bluestone assemblage at Stonehenge (and vicinity) is so varied that the increasingly convoluted idea of human transport over land and sea has to be dumped.  Are they going to "explain away" every new stone source, as it is discovered, by invoking some new and ever more wacky transport route?  Isn't it time that somebody at the Society took our two illustrious professors to one side and reminded them -- ever so gently -- that there are such things as glaciers?
 
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SALON - the Society of Antiquaries of London Online Newsletter
Salon 252: 28 March 2011

Zircon provides key to Stonehenge ‘bluestone’ sources


Our Fellow Dr Rob Ixer, of the University of Leicester, along with co-researchers Dr Richard Bevins, Keeper of Geology at Amgueddfa Cymru — National Museum Wales, and Dr Nick Pearce, Reader in Geochemistry at Aberystwyth University, have used the mineral zircon to pin down the provenance of some of the ‘bluestones’ that were used to form the first stone circle at Stonehenge.
‘Bluestone’ is the common name for spotted dolerite, which is blue-grey in colour when wet or freshly quarried. Also known as ‘preselite bluestone’, the source of these relatively rare igneous rocks was traced by the petrologist Herbert Thomas in 1923 to Carn Menyn, an outcrop in the Mynydd Preseli (Preseli Hills) of Pembrokeshire, where our Fellows Geoff Wainwright and Tim Darvill have been carrying out fieldwork for the last ten years.
However, not all of the orthostats that survive today from that first Stonehenge circle are made of preselite, and precise sources for some of the other ‘bluestones’ have proved harder to pin down because they consist of the much more abundant fine-grained rhyolites, tuffs and sandstones that are hard to tell apart under a microscope.
To crack this problem, Dr Ixer and his colleagues have built on recent research showing that igneous rocks from different magma flows contain differing amounts of the mineral zircon and have their own distinctive compositions. In a paper published in the March 2011 edition of the Journal of Archaeological Science, they show how the unique zircon signatures of the Stonehenge rhyolites enables the stones to be matched to outcrops within the Fishguard Volcanic Group. These exposures are found in an irregular band that crosses north Pembrokeshire some 8km to the north of the Mynydd Preseli, stretching from Crymych in the east to Strumble Head in the west. One particular rhyolite has been pinned down to an outcrop in a steep-sided valley near Pont Saeson.
The finding has implications for the route by which the stones were transported to Stonehenge. Previous theories have suggested an arduous overland haul south from the peaks of Mynydd Preseli to Milford Haven, and then by sea and river to Salisbury Plain. These new outcrops are only a short distance (c 5km) from the harbour at Newport: the overland journey would have been much shorter, but the voyage via the Irish Sea is considerably longer and potentially more hazardous.
Location map of north Pembrokeshire showing key localities as well as the outcrop of the Fishguard Volcanic Group in relation to the Mynydd Preseli. Possible source locations for the Stonehenge spotted dolerite bluestones are shown (see key for symbols).

Credit: Dr Richard Bevins, Keeper of Geology at Amgueddfa Cymru — National Museum Wales

Sunday, 27 March 2011

The Worton (Devizes) stone

Our intrepid stone hunter (Pete G) has found another stone, this time in Worton, Devizes.  Here is an image grabbed off Google:


Again, we don't know what the stone is made of, or where it came from.  How many such stones do you have in your catalogue, Pete?  Is such a list published anywhere?  If not, it should be -- and we should have some authoritative stone identifications, so that we can put some interpretations on them......  more and more intriguing!

Saturday, 26 March 2011

The Devensian ice margin in West Wales

In Jansson and Glasser's study of the Welsh Ice Cap (2008) the authors come up with a suggested LGM limit which is remarkably similar to mine, as shown above.  There are minor differences of detail, and the ice limit inland is difficult to fix with any certainty because it now looks as if the ice edge was not stationary at this margin for any length of time.  There is no terminal moraine that can be examined in the field -- just a "feather edge" of younger glacial deposits overlapping older glacial deposits.

As I have noted before, the Devensian ice did impinge on the South Pembrokeshire coast, south of Milford Haven.  However, it is uncertain whether this ice was thick enough to impound a glacial lake within the area we now know as the Milford Haven waterway.

More on Lake Brynberian

Thanks to Neil Glasser for a copy of the paper by Etienne et al 2006, concerning the sequence of pro-glacial lakes thought tom have been formed along the North Pembrokeshire coast during the advance of the Irish Sea Glacier at the time of the LGM.  On the map the purple tint shows Irish Sea till and related deposits, the yellow shows lake deposits, and the red tint shows the deposits of the Teifi Glacier, down as far as Llandysul.

It's a great map.  Click to enlarge.  The ice margin shown on the western part of the map is clearly wrong, but we'll let that pass...

Note that the supposed Lake Brynberian, impounded against the north face of Preseli. is thought to have overflowed via a col into the Rhosddu channel, at an altitude of c 220m.  That means that shoreline deposits, if they are present, should be along the 220m contour........

Next time I go for a walk along in that direction, I'll take a look.

Thursday, 24 March 2011

The Seend and Edington stones

Thanks to Pete's brilliance with that Street View thing, I was able to look at the stones in question from a great distance!  Here they are:

The top two images are from Seend, and the lower one is from Edington.  It's impossible to say from this distance what they may be made of ----  I await a diagnosis from some enthusiastic geologist!

Bluestones at Seend and Edington?

 Tony draws attention to this para in the Burl article:

"The theory for the transportation of the stones by glaciation is not without supporting evidence. There are unsubstantiated reports of bluestones having been found on Salisbury Plain not far from Stonehenge, at Seend and at Edington, and there is proof of at least one substantial dolerite deep in the mound of Boles long barrow, a Neolithic burial-place blocked up and abandoned centuries before the ring was contemplated. William Cunnington, the antiquarian and fair geologist who found it in 1801, also wrote something pertinent, implying that he had recognised not only the bluestone but other types of Preseli stone in the barrow: "a great variety of the stones found in an oblong barrow near this place that are of the same kind with several of those at Stonehenge." 

Does anybody know anything about these purported bluestones at Seend and Edington?   The former is W of Devizes, and the latter SW of Devizes.

Stonehenge: How did the stones get there?



I found this remarkably perceptive article by Aubrey Burl on the HistoryBookshop.com web site.  The date seems to be 2001.  It's a timely reminder that there ARE (and were, a decade ago) some archaeologists who are prepared to take geomorphology and geology seriously....

Stonehenge: How did the stones get there?

Aubrey Burl explains how the myth of the stones transported from south Wales to Salisbury Plain arose and why it is wrong
http://www.historybookshop.com/articles/commentary/stonehenge-myth-ht.asp


History is full of enjoyable myths but Stonehenge has too many. They mutate. Hardly had modern scholars got rid of the pre-Roman druids than those soothsayers reappeared in the guise of 3rd-millennium BCE astronomer-priests who are said to have designed the great circle as a celestial computer for the prediction of eclipses.

There are other common fallacies. The Greek explorer, Pytheas of Marseilles, who provided the first written account of Britain when he visited the islands c.300 BCE, is sometimes said to have visited Stonehenge. In fact, he landed near the splendid circle of Callanish in the Outer Hebrides 500 miles to the north. Just as mistakenly, Stonehenge is described as a British stone circle though it is not this at all, but rather an imitation in stone of a lintelled timber ring, with architectural influences from Brittany.

Perhaps the most persistent of these myths is that men ferried scores of enchanted Welsh stones hundreds of miles. Returning across the Irish Sea from the Wicklow mountains to their home in southern Britain some time after 3000 BCE, a group of gold- and copper-prospectors are said to have steered towards the landmark of the Preseli mountain range in south-west Wales. Regarding the Preselis as magical and their bluestones life-enhancing, the crews felt compelled to plunder them one by one for an intended megalithic sanctuary on Salisbury Plain. The romance has been repeated so many times in so many books that it has almost become fact.

But there is no substance to the story. The early third millennium BCE, when the great monument of Stonehenge was begun, was a pre-metal age which had little contact between Wales and Ireland. That came only with the discovery of Irish copper ores around 2500 BCE. Even then, there is no evidence for prospectors from mainland Britain visiting Ireland. What Irish gold or copper did reach Bronze-Age Wessex probably arrived in the form of ready-made axes and lunulae manufactured in Ireland and carried overseas by Irish traders.

The story of the transportation of the stones from Preseli is less than eighty years old. There is an alternative possible explanation, namely that glaciation was responsible for the appearance of the stones on Salisbury Plain. This is often discounted as many geologists argue that there is no proof of Pleistocene glaciation (from the era of the last Ice Age, which ended around 8000 BCE) on Salisbury Plain, and therefore there was no glaciation there at all. However, Geoffrey Kellaway, who in 1971 was one of the first to support the idea of glaciation, suggested in 1991 that the ice ages of the much earlier Pliocene Epoch (5.4 million to 1.6 million years ago) provided a more likely candidate for the event that transported the stones to the region.

Stonehenge consists of two kinds of stone: sarsen (Tertiary sandstone) and bluestone (various grades of dolerite, an igneous rock and other varieties of stone). The massive vertical pillars that one thinks of as archetypically Stonehenge are sarsens that originate from the Marlborough Downs eighteen miles to the north. There has been little controversy about them. As long ago as the seventeenth century the architect Inigo Jones (1573-1652) wrote, in a book published in 1655, the same kind of Stone whereof this Antiquity consists, may be found, especially about Aibury in North-Wiltshire, not many miles distant from it, where are not only quarries of the like stone, but also stones of far greater dimensions then any at Stonehenge, may be had.

He said nothing about the properties or source of the smaller bluestones. Perceptively, though, he did mock at a myth. 'For, as for that ridiculous Fable, of Merlins transporting the stones out of Ireland by Magick, it is an idle conceit'.

The 'ridiculous Fable' points to a geological fact, though an archaeological mistake. Unlike the sarsens, the source of the bluestones remained unknown for centuries until in 1923 the geologist H.H. Thomas deduced that the source was Carn Meini, 'the mound of stones', in the Preseli Mountains of Pembrokeshire. This immediately raised the question of how they made their journey from there to Salisbury Plain. The following year E.H. Stone remembered that Geoffrey of Monmouth's chronicle, more hysteria than history, had claimed in the twelfth century that Merlin had brought the stones of Stonehenge from Ireland. This, Stone speculated, was perhaps a half-remembered saga of Britain's first metal-workers returning from their search for ores in the Wicklows, using the Preselis as a landmark and carrying off boatloads of potent bluestones. But it was a conclusion based on a misunderstanding of Geoffrey of Monmouth. It was wrong about the type of stone and wrong about the prospectors.

In his History of the Kings of Britain, Geoffrey recorded that the Saxon leader Hengist of the fifth century AD treacherously slaughtered hundreds of British nobles at Salisbury. Their affronted war-leader, Aurelius Ambrosius, ordered a memorial to be erected on the site of the massacre. He sent for Merlin who advised, "If you want to grace the burial-place of these men with some lasting monument send for the Giant's Ring which is on Mount Killaurus in Ireland … The stones are enormous, and there is no one alive strong enough to move them". A British contingent went to Ireland but were unable to shift the pillars. Merlin laughed and "dismantled the stones more easily than you could ever believe" and erected them in a circle around the burial-place on Salisbury Plain.

It is a fable unique to Geoffrey. Earlier the same century, Henry of Huntingdon had remarked of Stonehenge, 'no one has been able to discover by what mechanism such vast masses of stone were elevated, nor for what purpose they were designed'. He did not mention Merlin, nor Wales. Three hundred years earlier the Welsh monk Nennius had written of the massacre but not of Merlin, Wales or Stonehenge.

Geoffrey, although probably a Welshman himself, said nothing about bluestones, nor the Preselis, nor even Wales. He did, though, emphasise that the stones were gigantic and beyond mortal strength, which surely suggests, even to the most sceptical reader, that he was referring to the sarsens - which are up to 30 feet long and weigh twenty tons or more - rather than the much smaller and five-times lighter bluestones. He may even have been unaware of them. Nor are they shown in a mid-fourteenth-century manuscript showing Merlin at work at Stonehenge.

Geoffrey's garbled report can be explained. Writing in the late seventeenth century the antiquarian John Aubrey remembered that, "Mr Gethin of the Middle Temple London, told me, that at Killian-hill (or a name like it) in Ireland, is a monument of Stones like those at Stone-heng; and from whence the old Tradition is that Merlin brought them to Stone-heng by Conjuration". He added in Latin that the pillars were "located on the plain, not far from Naas" in Co. Kildare. Some such menhirs do still exist, enormous grey, granite columns like Craddockstown West, 14.5ft high, Punchestown 17.5ft, and the 21ft high Longstone Rath. They were not in fact sarsens, but to the clerics travelling from England to St Brigid's Abbey in Kildare they did resemble them and seemed to be the remnants of a gigantic Irish ring that had been a quarry for the massive circle of Stonehenge. Merlin had carried the pillars away on his back, not stopping at the Preselis on his way.

In 1185, fifty years after Geoffrey's History, the Welsh cleric Giraldus Cambrensis saw the monstrous Irish menhirs on his way to visit the Kildare abbey and its magnificent illustrated manuscript, "'that wonderful book … so delicate and subtle". He was astonished by the size of the stones and wondered how they "were ever brought together"; it is obvious that it was their similarity to the Stonehenge sarsens, not the bluestones, that he and Geoffrey had in mind.

There was a dilemma. Geoffrey had the two ends of the story but lacked ways of bridging the 250 miles of land, sea and mountain between Kildare and Salisbury Plain. Aware that humans were incapable of freighting such huge pillars, the medieval chronicler turned to the equally acceptable superhuman. He invoked Merlin - the sixth-century seer Myrddin, already popular in Welsh legend and poetry - and it was that wizard who dismantled the stones and had them brought to Britain.

Once it is realised that Geoffrey was writing about sarsens being transported from Ireland, the farrago about talismanic bluestones from the Preselis is discredited. There are no sarsens on the Preselis. The Irish links with Stonehenge had nothing to do with the dolerite of the Preselis but everything to do with the mineralogical ignorance of medieval English visitors. The megalithic "epic" is merely wishful thinking.

Although the bluestones may have originated in the Preselis, the notion that humans moved them to Stonehenge is confronted by many archaeological difficulties. Transporting the bluestones from Wales to Wessex would have been a form of seafaring suicide. Metal prospectors, even in the third millennium, could quite feasibly have made such a journey with a manageable cargo of ores, travelling in easily-beached canoes, but in contrast the endeavours of crews attempting to manoeuvre a heavily-laden, clumsy raft along the seas of the Welsh coast would have been perilous in the extreme.

On a floating platform without sails, with propulsion dependent on paddles and poles, with little control over steering, and affected by every capricious current of the Bristol Channel, the crews would have faced the vicissitudes of weather and a recurring series of threats: strong tides, undertows, lethal sandbanks. Added to these difficulties is the fact that natives of land-locked Salisbury Plain are unlikely to have been experienced seafarers. To cope with the treacheries of the southern Welsh coastline and the swirling waves of the Irish Sea they would have needed the assistance of local fishermen knowledgeable about the currents and the signs of suitable weather.

Even at the end of the sea voyage further challenges remained. When the Bristol Avon had been reached the sea-going raft would have had to be abandoned and the stone transferred to a vessel more suited to narrow and winding rivers. Further on it would have had to be unloaded for an overland portage of several miles up exhausting slopes until the cargo could be lashed to a third craft for an up-river crawl along the twisting River Wylye - the 'tricky or treacherous stream'(according to the authors of The Place-Names of Wiltshire, 1970) - then northwards up the Christchurch Avon towards Salisbury Plain and Stonehenge. This unparalleled undertaking would have had to be repeated almost eighty times, over a period of many decades.

The demands of such an enterprise were underlined by the attempt by a group led by Phil Bowen and given lottery money last year to reproduce the journey. As a scientific experiment it was sadly flawed. From the beginning the project was compromised by a series of economies, precautions and shortcuts. A bluestone one ton lighter than any at Stonehenge was chosen. It was dragged on a sledge from the Preselis, though not over rough ground but along mesh-covered roads. A lorry was used to take the load over difficult slopes. At the coast the stone was lashed on a cradle between two lightweight curraghs or coracles instead of being laden onto a sensible, well-constructed raft. At the end of the intended voyage the team planned to avoid the challenge of rivers and an arduous cross-country haul by floating the cargo on a barge along the Kennet & Avon canal - not an option that would have been open to the people who built Stonehenge. Yet even with these spurious adaptations the mission ended abruptly just four miles out to sea when the stone slipped from its lashings, fell into the water and sank 60 feet to the muddy bottom of Freshwater Bay, Pembrokeshire, with its sharp currents.

The 'reconstruction' was an ill-researched, ill-prepared fiasco. But its failure does emphasise how difficult and dangerous a genuine adventure would have been. Whatever the method by which the stones arrived on Salisbury Plain, they were apparently set up in about 2800-2700 BCE inside a much older earthwork, in either an unfinished concentric circle or an incomplete horseshoe open to the southwest A century or so later (c.2500 BCE) the great sarsen circle was constructed, and the bluestones were dragged from their holes (called the Q and R Holes, after John Aubrey's Quaere) only to be returned some centuries later to form an irregular circle and an elegant horseshoe inside the towering sarsens. Some remain today in these positions. In 1983 a systematic archaeological search of the Preselis was undertaken to look for signs that the Stonehenge bluestones might have been quarried or removed. It concluded: "The field survey has not yet produced any direct evidence that the Stonehenge bluestones were quarried or collected from the Preseli Mountains in the third or second millennium BC". Yet the indisputable fact remains that stones originating in outcrops found in southwest Wales were used in an early phase of the building of Stonehenge.

If the people building the monument indeed brought them there, it was probably from close by, a few miles from Stonehenge where there was a convenient glacial deposit of the only stones among the chalk and flint of Salisbury Plain. Of the more than 1,300 stone circles in Britain, Ireland and Brittany, not one has stones brought from more than six miles away. There is no reason for Stonehenge to be an exception now that Preselis' 'magic mountain' has been shown to be irrelevant. To answer 'Stonehenge is unique' is a convenient evasion. Those who argue for the human-transportation thesis rarely explain why men would have chosen to transport crude blocks all that distance without first removing unwanted, heavy protrusions from the stones. Professor W. Judd asked this question in 1903, twenty years before H.H. Thomas: "The old tradition concerning Stonehenge [is] that it consisted of a circle of 'bluestones' which had acquired a certain sanctity in a distant locality, and had been transported from the original home of the tribe. If so, the stones, brought from so far away, would have been reduced to something like half their bulk … Is it conceivable that these skilful builders would have transported such blocks of stone in their rough state over mountains, hills and rivers (and possible over seas) in order to shape them at the point of erection?"

Yet whatever 'dressing' the stones received, occurred when they reached Stonehenge. The mass of bluestone chippings found there, 'the Stonehenge floor', testifies to that. In contrast, Judd continues, those who hauled the sarsens 'would appear to have left only the final dressing to be done after their transport', in spite of moving them a much shorter distance. Thomas attempted to answer this by suggesting that the chippings found on the site were the result of an original unshaped bluestone setting being smoothed later for a reconstructed ring, a conjecture that leaves Judd's criticism intact. Logic, though, insists that it would have made sense to lighten a stone at source, and this would also have made it easier to secure the half-shaped block for its long, perhaps stormy, journey.

As the 'magic mountains' in which the stones were found, the Preselis are doubly discounted: firstly by the Merlin story, and secondly because there was plenty of suitable stone much closer to Stonehenge. It was available to the north on the Marlborough Downs, to the south in Dorset and to the west in the Mendips, all less than a sixth of the distance to southwest Wales.

Meanwhile, about twelve miles west of Stonehenge in the vicinity of the Boles earthen long barrow near Warminster, there was a litter of glacially shifted stones from the Preselis. This has been known since 1801, when William Cunnington excavated the barrow and found a large bluestone buried deeply within it. So firmly accepted is the legend of human transportation that Cunnington's discovery is ignored or dismissed for a variety of reasons: it was the wrong stone; it was not a bluestone; it was deliberately concealed in the mound 4,000 years later by murderous Saxons. None is credible.

By the time that Stonehenge was built, men possessed a centuries-old expertise in recognising the best stone for their axes, and exploited sources as far apart as Land's End, the Lake District and north-eastern Ireland, while rejecting unsuitable stone such as sarsen or slate. It is inconceivable that for their first stone circle at Stonehenge, a prestigious monument that was to endure for lifetimes, the builders would casually accept not fine-grained durable stone but third-rate material such as tuffs, rhyolites and calcareous and volcanic ash, when excellent dolerite blocks were plentiful on the slopes of Carn Meini. Some of the Stonehenge bluestones were so imperfect that they weathered into stumps in a few years. Rather than envisaging the transportation of such rubbish these distances, it is probable that there was a muddle of good, bad and ugly stone within a few miles of Stonehenge, brought there naturally some millions of years earlier.

Believers in human work-gangs assert that the stones were taken from the Preselis because these stones were believed to have special powers. Yet those superstitious men searching for health-giving slabs were so incompetent that they also apparently chose the Altar Stone that now lies at the heart of Stonehenge. This also originated in south Wales, though not in the Preselis themselves but from about twenty miles away. It was not bluestone but sandstone of which an abundance was already available in the sarsens of the Marlborough Downs. It had no special shape, bore no arcane carvings. Yet this nondescript seven-ton slab was apparently selected and transported on the hazardous journey. More feasibly, surely, this stone simply lay among a clutter of others on Salisbury Plain.

The theory for the transportation of the stones by glaciation is not without supporting evidence. There are unsubstantiated reports of bluestones having been found on Salisbury Plain not far from Stonehenge, at Seend and at Edington, and there is proof of at least one substantial dolerite deep in the mound of Boles long barrow, a Neolithic burial-place blocked up and abandoned centuries before the ring was contemplated. William Cunnington, the antiquarian and fair geologist who found it in 1801, also wrote something pertinent, implying that he had recognised not only the bluestone but other types of Preseli stone in the barrow: "a great variety of the stones found in an oblong barrow near this place that are of the same kind with several of those at Stonehenge."

Other than the medley of 'bluestones', there is no variety at Stonehenge, just homogeneous sarsen. One wonders if Cunnington had also recognised rhyolites and tuffs in the barrow, neither of which are local to Salisbury Plain. Nor were the true bluestones, plain and spotted dolerite, ever thought to have special powers. There are stone circles around the Preselis, but they are built, like all circles, of stones in the immediate locality, dolerite being just one of a mixture of tuffs, rhyolites, sandstones and volcanic ashes. Only Gors-fawr, in the immediate vicinity of Carn Meini, was composed solely of dolerite and its moorland is strewn with the slabs.

To this long list of objections to the notion that human transportation accounts for the presence of the bluestones must be added the identity of the so-called 'prospectors'. Until recently they were believed to be the people known as Beaker Folk. The earliest peoples given this name were immigrants from the European mainland in the later third millennium who settled warily on Salisbury Plain, well away from Stonehenge and its natives. But their successors, users of the attractive sealing-wax red Wessex/Middle Rhine beakers, whence they take their name, were wealthy leaders with copper daggers and gold cruciform discs and button-caps. These people might conceivably have gone to the Preselis.

The authority on British beakers, David Clarke, thought so in 1970 when he wrote: It is at least possible that these powerful chieftains directing the trade and exploitation of Southern Ireland, by way of the Bristol Channel and South Welsh coast, may have had the Prescelly [sic] stones brought along the copper/gold route to Wiltshire and Stonehenge, remembering that Prescelly Top, at 1760 feet [537m], is every sailor's landmark on the shortest crossing from the gold bearing hills of Wexford - a veritable Welsh Olympus. When Clarke was writing in 1970, Stonehenge was still thought to have been an Early Bronze Age artefact, built about 2000 BCE. The makers of the elegant Wessex/Middle Rhine beakers were seen as having arrived in Britain around 2200-2100 BCE, a century or two before the impressive circle was erected.

Recent studies are in agreement with Clarke's chronology for the Beaker Folk if not for Stonehenge itself, accepting a date of 2300-2100 BCE for the beakers. Recent radiocarbon dates from Stonehenge, though, show that the sequence of its three megalithic phases was: (1) on or before 2700 BCE, the first bluestone setting was erected; (2) the bluestones were removed from the Q and R Holes and the imposing sarsen lintelled circle and trilithons were constructed around 2500 BCE; (3) finally, about 2250 BCE, the bluestones were restored as a circle and horseshoe inside the sarsens.

The fact that some of the stoneholes of the sarsens of 2500 BCE cut through the Q and R pits, demonstrates that the latter must be earlier than this date. This kills the notion of the Beaker Folk having brought the bluestones to the site. The 'prospectors' were as many as seven centuries years too late.

Pre-Beaker prospectors did not go to Ireland; they had no need. Theirs was not the time of gold or copper and there was already good stone for axes in Britain. Archeologically, there is no evidence of anyone who could have fetched the bluestones.

It has never been explained why the Q and R Holes project was left incomplete. The simplest explanation is that people found, to their dismay, that there were insufficient half-buried glacial dolerites, rhyolites, sandstones and tuffs for their ambitious Stonehenge project. In frustration they abandoned the scheme and turned to a more imposing source, the sarsens of the Marlborough Downs. Those massive stones were hauled laboriously over dry land by natives of Salisbury Plain who really did exist.







Teetering tors, damaged tors and denuded tors

On my visit to Dinas Mountain the other day I was forcefully struck by the differences between these three types of tors in North Pembrokeshire, in the proximity of the Devensian ice limit.

Where overriding ice has been more than 100m thick, old tors and monadnocks (and there are scores of them) in the St David's Peninsula area, around Pen Caer and in the Fishguard - Dinas - Newport area have been so heavily denuded that some are now reduced to low rounded knolls.  Some have craggy rock outcrops on them, but even these are seriously damaged.  Typical is Garn Fawr, near Pwllderi on the western side of Pen Caer:


In the next zone, further inland and on the uplands of Dinas Mountain and Carningli, where the ice was tens of metres thick rather than hundreds of metres thick,  tors have survived much better, and some are very craggy and spectacular, but most are very seriously damaged and "rearranged" by the pressure of ice and by demonstrable glacial erosion.  Glaciated ice-smoothed slabs are common, and here and there we can see deep gouges (although striations are extremely rare, because of the coarse and crystalline nature of many of the rock surfaces).  Occasionally we can see extensive areas of ice-moulded slabs, as at Garn Fawr (yes, another one!) on Dinas Mountain:


Finally, beyond the ice edge, we have the teetering tors which are in some cases so delicate and unstable that they could not have survived the assault of moving glacier ice 20,000 years ago.  There is only one of these left in Pembrokeshire -- Maiden Castle, a fragile and grotesque tor made of Ordovician rhyolite (once thought to be Precambrian) overlooking Treffgarn Gorge in the centre of the county:


Now obviously these three categories incorporate a lot of variation, depending on local rock-type and the original tor configurations etc, but by and large the morphology of these tors does confirm the conclusions drawn -- on a variety of other grounds -- as to where the ice edge was, and the intensity of glaciation during the Devensian glacial episode.

Wednesday, 23 March 2011

The Carn Meini stone river

Here is the Carn Meini stone stream or stone river, towards the left edge of the photo, and to the right of the winding stream cutting.  You can see that it runs downslope from one of the rocky outcrops at the western end of Carn Meini, within a broad depression.  There is no way that this could be a man-made feature.
Above is a splendid photo from Skinnyde -- taken somewhere on the Falklands.  The "stone river" near Carn Meini is very similar indeed, although archaeologists have speculated that it might be an ancient roadway or route used for the transport of bluestones downslope from the mythical bluestone quarry up among the rock outcrops.  

Here is a description of how stone runs are formed.

From Wikipedia:  A stone run is a conspicuous rock landform, a result of the erosion of particular rock varieties caused by myriad freezing-thawing cycles taking place in periglacial conditions during the last Ice Age.
The actual formation of stone runs involved no less than five processes: weathering, solifluction, frost heaving, frost sorting, and washing.  The stone runs are essentially different from moraines, rock glaciers, and rock flows or other rock phenomena involving the actual flow of rock blocks under stress that is sufficient to break down the cement or to cause crushing of the angularities and points of the boulders.

Boles Barrow / Bowls Barrow / Heytesbury 1

Bowls Barrow (or all that is left of it) is to the right of the small group of trees, with tank tracks running right round it.


Found this on the Modern Antiquarian, in a post from Rhiannon.  Grateful thanks:

"... the scale and nature of military interference is startling. [C.C.] most vividly remembers his first visit to Bowl's Barrow, one of the most important spot sites in the SPTA, where he found recent tracked-vehicle marks scouring deeply through its ditch and the "no-driving" sign squashed into the mud of the new track."

(from Managing for Effective Archaeological Conservation: The Example of Salisbury Plain Military Training Area. By Roy Canham and Christopher Chippindale, in Journal of Field Archaeology, Vol. 15, No. 1 (Spring, 1988), pp. 53-65.)

From Wilts CC site:

Details
Long barrow known as Bodelus Beorh in AD968 opened by W Cunnington 1800 & 1803, John Thurnam 1864, and W & H Cunnington 1885-6. Primary deposit of 14 skulls, 5 or more with bones in disorder. Remains of 7 or more oxen and a block of bluestone. 3 intrusive skeletons appear to be Saxon. Aubrey Burl argues that the bluestone was transported to the area by glaciation as Cunnington found the stone in 1801 and therefore it cannot have come from Stonehenge as earlier postulated.
Sources
Victoria County History 1 1 141(1) 1957 Grinsell, L.V.
Wiltshire Archaeological Magazine Vol 24, p104-25 1889 Cunnington, William (Jnr)
Wiltshire Archaeological Magazine Vol 41, p172-4
Wiltshire Archaeological Magazine Vol 42, p431-7
Wiltshire Archaeological Magazine Vol 47, p267
Archaeological Journal Vol 77, p82
The Ancient History of Wiltshire Vol 1, 87 1812 Hoare, Sir R.C.
Devizes Museum Cat2 22 Nos X90-1 1911 Cunnington, M E; Goddard, E H
Salisbury Museum 1934.68; 1934.73 1934 Salisbury Museum

Unfortunately I'm rather far from the National Library, and so can't easily check references -- doers anybody know this one?  If it really is 16 pp long, it may have some useful info in it.......

 Cunnington, B H, 1924, The Blue Stone from BolesBarrow, Wiltshire Archaeological and Natural History Magazine, 442, 431-47

The Boles Barrow Bluestone


Many thanks to Pete G for supplying these two excellent photos (date?) from the garden of Heytesbury House.  Purportedly this stone (used as a little garden seat in the shade of a mighty tree?) was the one that came from Boles Barrow, and which eventually found its way into Salisbury Museum.

There has been endless debate about its provenance, with Burl, Kellaway (and, I think, Richard Atkinson) happy about its provenance, but others (including Scourse and Green) claiming that it must have been robbed from Stonehenge.

Can anybody who has seen the stone in Salisbury Museum confirm that it is the same stone?  Pete reports that the museum will not allow photos to be taken of it.  Totally weird -- I wonder why?  Is national security at stake?

Tuesday, 22 March 2011

Perched blocks and glaciation

Carn Edward, near Carningli

Carnedd Meibion Owen, near Tycanol Wood

Garn Fawr, Dinas Mountain

Carn Arthur, near Carn Meini

Carn Enoch,  Dinas Mountain

These are all perched blocks found in NE Pembrokeshire.  They are not  ERRATICS since they are all of rather local origin, transported by ice for metres rather than kilometres.  Almost certainly the agency is glacier ice, although in some circumstances blocks can be dislodged from a cliff face or from a teetering tor and roll or slide down a snow slope, to be later "dropped down" onto a precarious situation as the snow melts away.  But I don't think this can have happened in any of these cases -- there are no convenient "source locations".  So glacier ice has actually moved these very heavy blocks, several tonnes in weight, and has left them behind when it melted.

Age?  Four of the photos come from the zone of "rearranged tors" affected by thin glacier ice at the peak of the Devensian glaciation, within a kilometre or two of the ice edge.  But the Carn Arthur perched block was reputedly hurled there from the other side of the Preseli Ridge by a giant or great hero called Arthur, in the good old days. (Hero names like Arthur or Samson are often used to explain strange natural phenomena.....)  If you don't go for that explanation, and prefer the glacial one, the interesting thing is that Carn Arthur is on the SOUTH side of the Preseli ridge, well to the south of the Devensian ice edge as we currently imagine it.  That means that the block was put into position during some earlier glaciation like the Anglian, maybe 400,000 years ago......

The Boles Barrow Bluestone Debate

Some letters from ancient history......

British Archaeology
Issue no 47, September 1999

LETTERS
Bluestone journey

From Dr Christopher Green

Sir: Glacial transport of the bluestones is less plausible than Aubrey Burl suggests (`Glaciers and the bluestones of Wales', June).
Although there is no other instance of people transporting megaliths over the distance from the Preselis to Stonehenge, many were transported over lesser distances. So the technical skills existed; the problem is the distance. Burl observes in his book, Great Stone Circles, when comparing the transportation of the bluestones and the Stonehenge sarsens, that the latter task was `much easier because the journey was all across dryland'. So why highlight the possible difficulties of a sea journey? Why not overland? It was technically possible - the question is why, not how.
Secondly, even if the bluestone in Salisbury Museum came from Boles Barrow, which remains unproven, where is the other glacial material on Salisbury Plain? It is inadequate to say, as Burl has, that `absence of evidence is not evidence of absence'. The rivers draining Salisbury Plain are flanked by terraces formed in the period when glaciers might have reached Salisbury Plain, and occupied by sediments derived from the surrounding landscape. If rocks were carried by glaciers to Salisbury Plain, they would occur in these sediments. In examining over 50,000 pebbles, I have found no glacially derived rocks. Burl must explain this, not dismiss it.
Thirdly, is the bluestone in Salisbury Museum from Boles Barrow? It is much larger (1,338lbs) than the stones recorded there by Cunnington (28-200lbs), and the ten stones taken by Cunnington to Heytesbury he described as sarsens. As Burl notes `Cunnington was . . . well able to distinguish between sarsen and dolerite'. There is no unequivocal evidence that the disputed bluestone was ever in Cunnington's possession. What we know is that it reached the grounds of Heytesbury House before 1860, supposedly from the nearby garden of Cunnington's house.
Yours sincerely,
CHRISTOPHER GREEN
Royal Holloway
University of London
14 June
 
From Prof Sean McGrail
Sir: Aubrey Burl argues that late Neolithic seamen (`kamikaze crews') would have been overwhelmed by natural hazards if they had attempted a coastal voyage with Stonehenge bluestones. The difficulties of such a passage should not be underestimated, but these seamen were descendants of people who had settled much of the British and Irish archipelago in some of the most difficult seas in the world, and there is every reason to think that they could have coped with the races, sands, rocks and shoals of the Bristol Channel and Severn Estuary.
They would certainly have used the tidal flows to advantage - the tide would, in fact, have been their prime mover, paddles being used mainly to steer and to avoid hazards. Furthermore, they would have chosen a period of settled summer weather.
What sort of craft might have been used is a more difficult question. Logboats are the only type of water transport we have direct evidence for before the mid-2nd millennium BC. Although the evidence that logboats were being joined together by 2000BC is slim, my preferred hypothesis would be three logboats linked together side by side, with a bluestone on the central boat and paddlers in the others. Such a vessel would give the best combination of buoyancy, freeboard, stability, speed and manoeuvrability, together with a reasonably robust structure and some protection for the crew.
Yours sincerely,
SEAN MCGRAIL
Salisbury
4 July
 
From Mr Stan Rendell
Sir: Aubrey Burl refers to Preseli bluestone erratics on the Bristol Channel islands of Flat Holm and Steep Holme. As Archaeological Advisor to the Kenneth Allsop Memorial Trust which owns and manages Steep Holme, I have to say that the fragments of `bluestone' announced in 1996 by the Trust's (then) Warden were nothing to do with Preseli.
Aside from serious doubts about how the sharp-edged fragments actually reached Steep Holme, the former Warden's confident assertion that these were of the same type of rock as the bluestones of Stonehenge was very quickly shown to be incorrect following hand specimen and thin section petrography by Dr Robert Ixer of Birmingham University.
Regarding Flat Holm, neither the Flat Holm Project Director nor I are aware of any fragments of Preseli bluestone on that island, although many other erratics have been identified on its pebble beaches.
Yours sincerely,
STAN RENDELL
Weston-super-Mare
22 June

Monday, 21 March 2011

Aubrey Burl on the Boles Barrow mystery

British Archaeology
no 45, June 1999

ESSAY
Glaciers and the bluestones of Wales
It was not human effort that brought them to Stonehenge, argues Aubrey Burl

Ever since the source of the Stonehenge bluestones was identified as the Preseli ridge in Pembrokeshire, it has been accepted that they could only have reached Salisbury Plain by human effort. Despite cogent arguments favouring glaciation, the majority of geologists have been firm that this was impossible, even though erratics from West Wales have been identified two-thirds of the way from the Preselis to Salisbury Plain at a site near Cardiff, and also on Flatholme and Steep Holme islands in the Bristol Channel less than 60 miles west of Stonehenge. Archaeologists have been even firmer in their belief in an almost superhuman feat of men transferring some 80 heavy slabs a distance of over 200 miles.
Data from standing stones, circles and tombs reveal that prehistoric societies did not fetch massive blocks from any great distance. Where there was convenient stone they used stone. Where there was not they used timber or earth.
There has been little serious consideration of the logistics involved in the hypothetical journey from Wales to Wiltshire. The most meticulous was by Richard Atkinson. In his scheme, the stones were brought by land and river to Milford Haven, floated along the shores of South Wales and up the Severn, and then taken by rivers and land-portage up to Stonehenge. He suggested the use of a pine raft with a crew of twelve. A modification of his description would envisage a tree-trunk platform about 6m square, constructed for buoyancy in three layers, each of 20 logs 6m long and 0.3m thick. With a dry weight of 35lb per 0.03m3 the logs would have weighed about 20 tons and the entire cargo of wood, stone and men over 30 tons. Whether this unwieldy craft was seaworthy and capable of being manoeuvred during the day and beached night after night by a small crew is doubtful.
On a floating platform without sails, with propulsion dependent on paddles and poles, with little control over steering, affected by every capricious current of the Atlantic Ocean and Bristol Channel, the kamikaze crews faced daunting challenges. Once out of the shelter of Milford Haven, almost immediately the voyagers would have encountered strong tides and under-tows across the dangerous waters surging southwards near Freshwater West. Tidal flows of three to five knots streamed on the east side of Carmarthen Bay, and beyond them were treacherous sandbanks at Cafn Sidon Sands. Between Carmarthen and Swansea Bays heavy currents swirled at every headland. A mile from the coast off Ogmore-by-Sea lay the reef of Tusker Rock on which many mechanicallypowered ships later foundered.
Even when the mouth of the Severn was reached the struggle was not done. The river could pour seawards at up to ten knots, there were submerged mudbanks, the highest rise and fall of tides anywhere in the British Isles, all this before the Bristol Avon was reached at Portishead. At that point the stone would have to be transferred to something more suitable for travel along narrow and winding rivers. Further miles against the current took the vessel to Frome where everything again had to be disembarked for a portage that required a work-gang to drag the stone some eight or nine miles over land rising persistently to Warminster. There the cargo was replaced in the reassembled craft for another up-river crawl to West Amesbury, and once again unloaded and hauled up the chalk slopes to Stonehenge. This unprecedented undertaking had to be repeated almost 80 times.
The truth is, rather, that no such undertaking was necessary. The most compelling evidence for glacial transport of the bluestones is that at least one substantial block was on Salisbury Plain centuries before the construction of Stonehenge. It lay in the Neolithic Boles Barrow which had been blocked up and abandoned long before the bluestone circle was erected. Following his excavation of Boles Barrow of 1801, William Cunnington wrote of the barrow's `large stones' amongst which he discovered a `Blue hard stone ye same as the upright Stones in ye inner circle at Stonehenge'. For his period, Cunnington was a competent geologist, well able to distinguish between sarsen and dolerite. He removed ten stones from the barrow and arranged them in a circle in his garden at Heytesbury. After his death, a bluestone was taken from his garden to Heytesbury House. From there, it was given to the Salisbury and South Wiltshire Museum by Siegfried Sassoon in 1934.
It has been argued that the bluestone in the Salisbury Museum came from Stonehenge, not from Boles Barrow. This, however, is contradicted by a statement of Flinders Petrie, later the famous Egyptologist, who in 1877 made a punctilious survey of Stonehenge. As a result, he was able to assert `entirely confidently' that `No stones are missing since Wood's plan'. John Wood had made the first really accurate plan of Stonehenge in 1740, distinguishing between stones that were erect, leaning, flat, buried, and lying on the surface of other stones. He is unlikely to have left a largish bluestone unplanned, especially as he had plotted stone 32 at the east of the bluestone circle, a stump no bigger than Cunnington's. Scrutiny of the two plans shows that Petrie was right. No stone is missing. As Cunnington found his stone in 1801 it cannot have come from Stonehenge. The evidence is clear-cut. It does not support belief in human transportation of the bluestones from south-west Wales.

Dr Aubrey Burl is an expert on stone circles and a former sailor. This is an edited extract from his book, Great Stone Circles, recently published by Yale (£19.99) 

See also:  Cunnington, B H, 1924, The Blue Stone from BolesBarrow, Wiltshire Archaeological and Natural History Magazine, 442, 431-47

The Stonehenge Moraine?

Looking afresh at the Judd article from 1903, and recalling the ideas of Geoffrey Kellaway, maybe the time is right to resurrect the question of whether there might have been a moraine at or near Stonehenge, laid down a very long time ago (during the Anglian Glaciation) at the easternmost extremity of Irish Sea Glacier advance.

I know that certain geomorphologists, including Prof James Scourse, Prof David Bowen and Dr Chris Green, have rubbished this idea with great enthusiasm, claiming that it is glaciologically implausible and unsupported by any field evidence.  As I recall, all three of them have used the word "impossible" -- causing me to recoil in horror and the archaeological establishment to rub its hands in glee.

But Wesley John Judd (he must have been a good Methodist, with a name like that, so maybe he enjoyed divine inspiration) was no fool.  Look carefully again at his paper.  He clearly was not too sure where the ice had come from (north or west, or maybe north-west) but he clearly had suspicions that the assemblage of debris at Stonehenge had come from North Pembs or North Wales.  He also observed that in areas affected by very ancient glaciations, most of the till would have been eroded away by river action and solifluction after hundreds of thousands of years, leaving only a thin scatter of erratics here and there.  Further, he observed that scattered hard stones (including bluestones) left behind on Salisbury Plain would have been targetted down through the centuries for building purposes, millstones etc -- and this was a point also made quite forcefully by Olwen Williams-Thorpe and her colleagues during the Open University studies around 1990.

Things get even more interesting when we look at his identifications of stones.  He seems to have concentrated not on the bluestone monoliths or orthostats themselves, but on the debitage or debris in the Stonehenge soil layer.  And what did he identify?  An extraordinary assortment of "rubbish stones" including fissile sandstones, micaceous sandstones, greywackes (argillaceous and easily broken down), flagstones, slates and "clay-slates", and fine-grained glauconitic sandstones.  He made the point specifically that all this material did not seem to be very closely related to the remaining standing bluestones -- so he concluded that only the hardest stones had survived to the present day, with all the rubbish material breaking down and becoming incorporated into the soil layer over many thousands of years.

What if all that debris was in the soil layer long before Stonehenge was built?  It's perfectly feasible. Might we therefore be looking at the remains of an ancient till deposit, or even a moraine?  Judd himself seemed to think -- right at the end of his note -- that the presence of this feature -- with an abundance of foreign stones readily available to the builders of Stonehenge -- might have actually determined the precise position of the monument.  Nothing to do with ley lines or astronomy or anything else of an esoteric nature -- straightforward opportunism on the part of the tribes who lived on Salisbury Plain.

Now I'm not familiar with all of the details of the current geology, and I need advice on all of this, but it seems that there are clues in the recent work published by Rob Ixer and Richard Bevins that suggest that Judd was pretty much on the ball.  They have already said in print that much of the debitage is unrelated to the nature of the bluestone monoliths.............



One further intriguing thought comes into my head.  It's difficult to know from Judd's descriptions precisely which sedimentary and metamorphic rock types he is talking about -- names have changed over the years.  But when he talks of fissile sandstones, greywackes, slates, flagstones, clay-slates and so forth he could well be describing the non-volcanic rock types that occur in association with the Fishguard Volcanics in the eastern Preseli Hills and Dinas-Newport area of North Pembrokeshire.  If you walk around the area today the intervening areas between the volcanic and intrusive rock outcrops (the rhyolites and dolerites) are underlain by shales, mudstones, sandstones and ash beds, sometimes in an unaltered sedimentary state, sometimes partly metamorphosed, and sometimes transformed into slate.

So could this non-igneous debitage also have come from this same narrow zone (about 3 km wide) which I have already speculated on as a possible zone of entrainment between Welsh Ice and Irish Sea ice at the time of the Anglian glacial episode?

More and more intriguing --- watch this space.

Gowland and Judd 1903




Rob asked me for the link to the original archive file with the Gowland / Judd paper in it, dating from 1903.

Here it is:

http://www.archive.org/stream/wiltshirearchaeo33arch#page/n7/mode/2up

On ancient shorelines



When I was a young researcher, I spent a lot of time hunting for shorelines -- in Iceland, Greenland, Antarctica and Norway -- and in the UK as well.  If one can find them, they can tell one a lot about events related to glaciation in general, and glacier retreat in particular.

Raised shorelines can either be related to  sea-level (if there is access to the open coast) or to pro-glacial lakes, which tend to form in "closed" situations where water levels can oscillate rapidly and where catastophic drainage can sometimes occur.  Quite literally, one year an ice-dammed lake  maybe 200m deep may be there, and the next year it's gone.  Some lakes can fill and empty over and again, causing some confusion in the interpretation of shorelines or "washing limits."  But the general rule is that the highest shorelines are the oldest, and the lowest ones are the youngest.  Another rule is that where there is isostatic readjustment going on, the highest shorelines (if you can trace them along many miles of a shore) will have the highest tilts, and the lowest ones will be increasingly closer to horizontal. Where you find sets of shorelines, they can intersect.  In general, if you find a shoreline you assume that it represents some sort of stillstand which coincides with a stabilisation of ice volumes over maybe decades or centuries.  But the speed of development of a shoreline will depend on the amount of wave action on a shore, the annual length of the ice-free season (when the surface of the water is free of ice), the fetch, and the nature of the shore itself.  A sediment shore will leave traces of a stillstand far better than s steeply-sloping clean bedrock shore.  You have to think in all dimensions -- and interpreting shorelines involves a highly complex sort of multivariate analysis.

The pictures above show the 3 shorelines of the Parallel Roads of Glen Roy, in Scotland, a set of shorelines alongside a pro-glacial lake in South Georgia, and a shoreline (yes, that's me in 1966!) in the South Shetland Islands, Antarctica.

This info is all relevant when it comes to trying to work out where the Devensian ice limit was in SW Britain, since there is much talk of lakes particularly on the southern coasts of Cardigan Bay. (See the earlier posts relating to the South Wales End Moraine, Glacial Lake Teifi and "Lake Brynberian"........)

In spite of years of hunting, I have never found anything that I would call with any certainty a glacial lake shoreline, either in the Teifi Valley or the Nevern Valley.  I'm pretty sure that this means the glacial lake inundations were VERY short-lived, with no water level static enough, over a long enough period of time, for the formation of shorelines.  As I have suggested earlier, the answer may lie in the varves.  But I'm still putting my money on the ice remaining at its maximum position for no longer than a few decades.

Another complication, with Lake Teifi and maybe the other North Pembrokeshire lakes, was that maybe the oldest shorelines were lower than the youngest ones -- with the suite of shorelines representing a gradually rising water-level as the ice advanced across valley mouths and meltwater accumulated to higher and higher levels as the ice dam became stronger.

Saturday, 19 March 2011

Judd on the stones of Stonehenge


Following on from my last post, I have scanned in some of the key pages from this 1903 article by Prof Judd, contained within the longer piece by William Gowland.  Judd is particularly concerned about the debris or "debitage" at Stonehenge, and his analysis is remarkable for its time.  He also considers the broader issue of the nature of the standing bluestones and stumps, and discusses the frequency of particular rock types, their possible source areas, and the mode of transport to the site.  He is in no doubt that the stones are glacial erratics, and indeed he makes a persuasive case that there was once a far greater quantity of glacial material in the Stonehenge neighbourhood -- subsequently largely removed through human intervention and (for the softer and more flaky stones at least) through the work of frost, rain and weather in general.  Here are the key pages.  With a bit of luck, if you click on them you will be able to enlarge on your browser.


Given that this article was written a long time ago, we will all part company with Judd on a number of issues, and of course he was not too familiar at the time with either the details of regional geology or the directions of ice movement.   But a remarkable article nonetheless....

See also my older post about Sir Archibald Geikie and the other geologists who were trying to work out ice directions in the period 1895-1905:

Friday, 18 March 2011

Judd the Prophet

Many thanks to Pete G for alerting me to this article, and to Wiltshire Archaeology for making it available on the web.  It's Gowland's report of the 1901 excavations -- highly impressive and full of interesting titbits of information.  He discusses alternative theories and possibilities in a remarkably balanced way -- something which later ceased to be possible, following the publication of HH Thomas's infamous paper and the wholesale conversion of the archaeology establishment to the new religion as laid down in the Gospel According to St Thomas.
 Incorporated into the Gowland paper is a long "Note on the Nature and Origin of the Rock-Fragments found in  the Excavations" by Professor JW Judd.  Again, it is remarkably sophisticated, with a number of points coming out of it quite clearly:

1.  The bluestones (as they were already being called) were from a wide variety of different locations and incorporated many different rock types.  (This fact was later overlooked by people like Atkinson who were obsessed with the idea that they had all come from around Carn Meini.)

2.  There was no reason why the bluestones should not be considered to be glacial erratics.  This is how Gowland summarised Judd's views:


3.  There was such a vast quantity of bluestone fragments in the soil layers at Stonehenge that the stones must have been dressed on the site.  Judd argued -- perfectly reasonably -- that if (as was already being proposed) the stones had been transported by the builders of Stonehenge from a long way off, they would surely have dressed the stones first, so as to reduce the weight of material to be hauled.

4.  Following on from that,  Judd argued that the stones might not have been moved far at all, and that Stonehenge might simply have been built where there just happened to be a nice assemblage of both sarsens and bluestones.

A man after my own heart!  On another post I'll publish some of the pages of the Judd manuscript.

Thursday, 17 March 2011

Snowmen at Stonehenge



Now here's a funny thing.  I was talking to a friend the other day, and he said he had been talking to a female friend of his about certain Stonehenge matters.   She is one of those people who "knows things" that other people don't know.  The talk drifted to the moving and erection of the stones (particularly the sarsens) and she said she knew exactly how how the sarsens had been moved and put up, and how the lintels had been put in place.  She said it was all winter activity, when there were no crops to be cultivated and when there was plenty of labour about.  She said she could "see"all of this, while in a state of heightened consciousness.   The stones were simply slid along on the ice and frozen snow, and slid into previously prepared holes.  They didn't bother with timber, but when a lintel had to be lifted into place they simply built a snow ramp, slid the stone up it and put it in position.  Then next spring the snow ramp would simply melt away, leaving no trace of the engineering operation behind.

Well, that all sounds very jolly, until you actually start to think about the practicalities......

But it's a nice idea, which comes a bit closer to the glacial theory than some of the other ideas doing the rounds!

Tuesday, 15 March 2011

Times Article



Just seen the latest Times article by Times Archaeology correspondent Norman Hammond.  He says:  "The notion that the bluestones were brought from Wales to Wiltshire by glaciers during the Ice Age is now discounted."  Hum hum.  By whom, I wonder?  Maybe by Mr Hammond and his "contacts" in the archaeology establishment.  He thinks that the new geology reported by Rob Ixer and Richard Bevins supports the idea of sea transport of the stones via Newport!!  Oh dear oh dear -- talk about looking at the end of your nose without seeing it.....

So the archaeology bods will now be searching high and low for twenty or thirty bluestone quarries, and a nice stone exporting harbour somewhere in the Nevern Estuary?

Thursday, 10 March 2011

On ice directions

 Many thanks to my friend Mike Walker for forwarding a PDF of this excellent and comprehensive chapter on the Quaternary.  It dates from 2006 -- and if we home in on West Wales we will see that almost everybody now agrees on a Devensian ice limit somewhat similar to that shown.  Mine differs only in that it incorporates the ice-contact tills at West Angle and the kame terrace at Mullock Bridge, which both show that the ice pressed into the mouth of Milford Haven.

Now for a little gripe.  Why do quite senior academics continue to show ice movements parallel with ice margins?  That just does not happen, except in the rarest of circumstances, where topography (eg a scarp or a deep glacial trough) forces glacier flow.  The ice did NOT flow across western Pembrokeshire from NE towards SW.  Has anybody recorded striations or erratic transport in that direction?  Not that I know of.  No -- the ice behaved as ice always does, and flowed perpendicular to the ice edge.  That is, it came in from the NW and flowed towards the SE, with minor variations forced by landforms.

Have you got that, chaps?


Reference:
Catt, J.A., Gibbard, P.L., Lowe, J.J., McCarroll, D., Scourse, J.D.,Walker, M.J.C., Wymer, J.
J., 2006. Quaternary, ice sheets and their legacy. In: Brenchley, P.J., Rawson, P.F.
(Eds.), The Geology of England and Wales, second ed. The Geological Society,
London, pp. 429-467.

Wednesday, 9 March 2011

Cosmogenic dating sites

This is the map published by Danny McCarroll and others in 2010 to show the location of the sites used for cosmogenic dating of rock surfaces.  Click to enlarge.  Below is my map of the Pembrokeshire Devensian limit.  According to this map ALL of the sampled sites in Pembrokeshire lie within the glacial limit and were thus subject to glacial erosion and/or glacial protection from cosmic radiation.

Tuesday, 8 March 2011

Glaciation of Carningli -- a dating problem

Perched block on Carn Edward, one of the sampled sites supposedly outside the Devensian ice limit


Now then.  We have a problem.  These are the cosmogenic dates published by McCarroll et al in 2010:

Pembroke, SW Wales  (inside LGM limit)

CF-01 SM977376  Carn Fran, nr Fishguard.  Age 35,280
CO-01 SM889380   Pwllderi clifftop, nr Trefasser.  Age 33,370
PF-01 SM999374  Cwm Mawr, Dinas.  Age  33,510  
PM-01 SM883396  Pen Brush, Pencaer. Age  76,820

Outside LGM limit
West Preseli Hills, Pembroke, SW Wales

MC-01 SN052374  Carnedd Fychan, Carningli Common.  Age   107,100
MC-02 SN055372  Carn Llwyd, Carningli Common.  Age   152,600
MC-03 SN054365  Carn Edward, Carningli Common.  Age    129,500

.......... and here is what they say about the sites and the dates:

Geomorphological evidence (Catt et al., 2006) indicates that the
eastern LGM limit of the ISIS lay along the north Pembroke coast
(Fig. 1). East of the proposed ice limit, the western Preseli Hills
(Mynydd Carningli) show no evidence of glaciation, and the landscape
is dominated by tors rising above autochthonous blockfields
(Walker and McCarroll, 2001). Closer to the coast, however, rocky
knolls are conspicuously ice-scoured and glacial deposits derived
from the Irish Sea basin are widespread (Hiemstra et al., 2005).
Three samples collected from basaltic tors on the west Preseli Hills
(MC-01, MC-02, MC-03) all yielded minimum 36Cl ages >100 ka
(Table 3), consistent with the inference that this area escaped
glaciation during the LGM. Two samples (CF-01, CO-01) from icemoulded
outcrops on coastal headlands just within the proposed
glacial limit produced 10Be ages of 35.3   3.6 to 38.0   4.8 ka and
33.4   3.6 to 35.9   4.7 ka and two further samples (PF-01 and PM-
01) gave 36Cl ages of 33.5   2.6 ka and 76.8   7.2 ka. Although three
of these ages are internally consistent and all are significantly
younger than those obtained from the Preseli tors, all are significantly
older than the LGM, and thus conflict with the geomorphological
evidence for over-running of the north Pembroke coast
by the ISIS during the LGM. We infer that all four ages are
augmented by nuclide inheritance due to insufficient removal of
bedrock by glacial erosion, and thus provide no information on the
timing of ice retreat.


Now I don't like to argue with senior academics, but something is wrong here.  Admittedly the authors of the paper do not know the territory as I do, but to say "East of the proposed ice limit, the western Preseli Hills (Mynydd Carningli) show no evidence of glaciation" is simply wrong.  As I have shown on a number of the posts on this blog,  Carningli supports abundant evidence of glaciation -- and relatively recent glaciation at that.  There are multiple ice-smoothed slabs and other rock surfaces, perched blocks, a moraine ridge near Pont Ceunant, lateral morainic ridges on the NE face of Carningli, and a thin spread of till with many sub-rounded boulders and cobbles on the eastern flank of the mountain.  These features can only be explained by glaciation during the Devensian, with all but the highest part of Carningli inundated by ice -- even if the ice cover lasted only for a few centuries or decades.

"Three samples collected from basaltic tors on the west Preseli Hills......"  Hm.  Sorry guys, but there are no basaltic tors here at all -- they are all made of rhyolite, dolerite and assorted complex volcanic deposits related to the Fishguard Volcanic series.  No basalt.


And the dates themselves are very confusing.  The dates from the coastal areas west and east of Fishguard (inside the LGM ice limit) come out at between 32,000 and 77,000 years BP, with quite large margins of error.  The grid references are not adequate to locate the sampling points with any precision -- so we do not know what likelihood there may have been for snow protection or vegetation protection -- maybe for prolonged periods in the past.  We will not dispute the assumption that all these sampling points WERE glaciated during the Devensian -- but the dates tell us nothing about when the ice arrived, when it melted away, and how much erosion there might have been on the sampled rock surfaces.

The three dates from Carningli Common (Carnedd Fychan, Carn Llwyd and Carn Edward) are even more confusing, since they all show dates in excess of 100,000 years.  As indicated above, the sampling points (like those nearer the coast) WERE glaciated during the Devensian.  So why are the "exposure ages" so much greater?  It might be reasonable to assume that there would have been more glacial erosion, over a greater period of time, near the coast than near the top of the Carningli upland ridge -- so all I can assume is that the dates are highly misleading, and that they simply show us some sort of "nuclide inheritance" as suggested by the authors.  Might the dates reflect very old weathered rock surfaces from which maybe 10mm of rock has been removed by erosion near the coast, with maybe 1 mm of rock removed from the rock outcrops near the crest of the Carningli ridge?

An interesting puzzle....  I need advice from somebody who understands cosmogenic bombardment and penetration into rock surfaces of various types!

Reference:
Exposure-age constraints on the extent, timing and rate of retreat of the last Irish Sea ice stream.
Danny McCarroll, John O. Stone, Colin K. Ballantyne, James D. Scourse, L. Keith Fifield, David J.A. Evans, John F. Hiemstra,
Quaternary Science Reviews xxx (2010) 1-9

Monday, 7 March 2011

The Glaciation of Carningli



 

The main features of the geomorphology of Carningli.  Top:  Photo of the mountain from the W, showing the glaciated flanks and the nunatak coincifing with the highest peaks.
Middle:  a satellite image of the whole of the mountain.  The arrows show the approx directions of ice movement at the peak of the Devensian Glaciation, c 20,000 years ago.  The dotted area shows the extent of the nunatak which appears not to have been submerged by ice on this occasion. A= areas of ice-smoothed bedrock slabs. B= area of rough lateral moraines left by successively lower ice margin positions during ice wastage. C= probable windscoop area, now marked by a steep scree slope with much frost-shattered debris. The windscoop probably formed some time after the onset of deglaciation.   D= areas swept clean by eroding ice moving round the flanks of the mountain.

The lower image shows the northern end of the mountain in more detail.  The prominent ridge-like feature is not natural -- this is the defensive wall of the Iron Age Carningli Village.  The rock platforms on which the village is located probably were covered by flowing ice at the peak of the glacial phase, but melted out relatively early.

Click on any of the images if you want to enlarge it.