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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Friday, 17 November 2017

Collapsing iceberg arch

I have been watching some of the videos on YouTube of collapsing ice fronts, rolling icebergs and iceberg arches giving way -- now that Arctic cruises are immensely popular, social media are full of snippets of film of "exciting" ice front events and of boats getting rather too close to the action.  There have been some close shaves -- members of the public (and even tour operators) seem to have little idea what natural forces are being unleashed when thousands of tonnes of ice fall into the water. The resultant displacement waves are quite high enough to wash people off rocks where they may be standing, or to turn boats over -- as I tried to demonstrate in my novel "Acts of God".

Anyway, people scream, shout and clap -- and gasp with relief when they manage to escape big waves that threaten to overtake their rapidly retreating boats. But one day there will be a big accident, because tidewater ice edges have become rather too popular with adrenalin junkies........

In principle, I don't have a problem with people getting close to glaciers and developing some understanding of how glaciers work.  And tour operators should certainly be informing as many people as possible about accelerating glacier retreat and the link with global warming.  Sadly, there is too much junk science around -- the fact that an iceberg rolls over, or an arch collapses, or a glacier front suffers a sudden catastrophic failure, does not in itself indicate that this is a "global warming event".   This is all perfectly normal glacier and iceberg behaviour -- and these things happen whether a glacier is advancing or retreating in a deep water situation.

The picture above is from one of the videos,  showing a big chunk of ice falling from an arch -- it would not have been a good idea to be beneath it in a kayak (or any other craft) at the time!  Over the next minute or two, after this photo was taken, the arch lost more and more of its mass in a welter of falls big and small, until it completely disappeared.  Then, of course, the remaining parts of the iceberg made major readjustments by rolling in the water, surrounded by a great apron of brash ice.

Monday, 6 November 2017

Stonehenge -- the authorised version (again)

Julian Richard's new book came out at the end of September.  It's called "Stonehenge -- the story so far", published by Historic England at £22.95 (or whatever), hardcover, 352 pp.

You can read bits of it if you look on the Amazon web site. It's very nicely packaged, with attractive photos and diagrams, and a modern page design.  But what about the text?  Well, from what one can see, we have the same old stuff as usual.  A friend very kindly sent me the text as it relates to the bluestones, in a section dealing with "sourcing and transporting the raw materials".  I am not impressed, since what we have --yet again -- is evidence of an author who is desperate not to rock the boat or to allow for any questioning of the fondly-held assumptions of decades.  Is this bland acceptance of the authorised version something that Historic England insists upon? Is it really true that it cannot admit to any disputes in an "official" publication? Does it really think that Joe Public cannot handle honest academic debate, in which there might be two (at least)  perfectly feasible explanations for one or another of the features at Stonehenge? I should have thought that honesty on this score would excite interest and enthusiasm for our historic heritage, rather then damping it down.........

So what does JR have to say?  Immediately we are into the ruling hypothesis, with confirmation bias flagged up for all to see. We are introduced to Carn Meini (Menyn) which is described as a place of "convenient slabs and pillars." JR continues excitedly: " In this showroom for monoliths tempting stones lie everywhere; some even look as if they have been propped up and are ready for loading onto a sledge for the start of their long journey - perhaps more stones intended for Stonehenge that never made it?" Oh dear. He forgets to tell us that there are at least a dozen other tors in the general area for which exactly the same words could be used.

He then goes on to talk of the geological provenancing, without any mention of the work of Ixer and Bevins, and he actually misrepresents their findings. They will surely not be amused.  Spotted dolerite does not just come from Carn Goedog and Cerrig Marchogion, as he implies. And the rhyolite at Rhosyfelin does NOT provide an "exact match" for bluestone fragments at Stonehenge. Quote: "At this outcrop excavations have shown where a pillar of stone was removed from the rock face, the quarrying dated by radiocarbon to c 3400 - 3300BC."  That weird "pillar" of stone and its "extraction point" pop up all the time, promoted by people who cannot be bothered to apply any scrutiny.  Has Julian Richards or any of the others who promote this nonsense ever been to the site and looked at the narrow natural fissure in the rock face that clearly has nothing whatsoever to do with monoliths or extraction points?  It was dreamed up by MPP in a moment of mad enthusiasm, simply because it was close to sampling point 8 used by Rob Ixer and Richard Bevins, and it has been re-imagined ever since by people who seem to have left their common sense behind.

And the radiocarbon evidence?  Most thoughtful human beings might think "It just doesn't fit.  Therefore, since there is no other evidence of quarrying anyway, we might as well give up on the quarrying thesis and think of something else instead."  But these archaeologists are made of sterner stuff.  "No, since we have already decided that this is a Neolithic quarry, we just have to shift the date back by a few centuries and work out what happened to all those nice bluestones before they were shifted to Stonehenge.  So we have to assume there was a convenient proto-Stonehenge somewhere in the vicinity....." Once these archaeologists have a nice ruling hypothesis to play with, there is no way they are going to abandon it.

And just as the geologists are going to be pretty angry about being ignored, we geomorphologists are also extremely displeased.  For Richards to trot out the quarrying story without question, in the full knowledge that there are two peer-reviewed papers in print which question every single bit of "evidence" presented by the archaeologists in one extremely dodgy "Antiquity" article, is not just careless but also disrespectful and deliberately misleading.  The author had two years to incorporate our findings into his text, and chose instead to ignore them.

Interestingly, having applied no scrutiny whatsoever to the quarrying hypothesis, Richards does devote considerable space to the glacial transport hypothesis.  So he does at least acknowledge that there are two competing theories.  But there is a complete lack of balance in the way he treats them.  He simply repeats the usual arguments about the Boles Barrow stone, the apparent lack of other erratics on Salisbury Plain, and the Christopher Green pebble counts. "Quite simply," says our intrepid author, "the theory of glacial transport does not stand up to scrutiny and should be dismissed."  And he concludes his section with a summary of the ideas of MPP, TD and others about highly prized or magic stones being brought to Stonehenge as a great sacred or symbolic gesture.

That's the authorised story, and Richards is sticking to it, come hell or high water.  If you are still tempted to buy this book, you will, I think, never find a better example of selective evidence citation and confirmation bias.

Friday, 3 November 2017

From the world-famous Rhosyfelin School of Archaeology.....

No comment needed........

Picton Point -- old glacial deposits?

Pembrokeshire geology map with the addition of a speculative flowline for the Irish Sea ice which might have affected the region around Picton Point

Picton Point is the south-facing headland that separates the western Cleddau and the Eastern Cleddau, in the tidal inner reaches of the Milford Haven waterway.  It's a delightful spot, with wide vistas to west, south and east.  My wife and I went over there for a walk the other day, and I was struck -- not for the first time -- by the frequency of erratic boulders and cobbles scattered along the shoreline.  These have not been carried here by longshore drift or by the tides -- there is very little wave action here.  So the erratics have dropped out of pre-existing glacial and fluvioglacial deposits as the low cliffs are nibbled away.

The main processes here (as at Mill Bay, the famous place from which the Altar Stone was supposed to have come) are biological and mechanical.  Tree roots are exposed as the Coal Measures sandstones and shales are sapped or undercut; then the trees tip over more and more until they fall down onto the beach; when that happens, loose rock debris on the cliffline ( already broken up to some degree by vast and expanding root systems) is dislodged and comes crashing down too, resulting in coastal retreat by a few more feet.  And so the process continues.  On the land surface above the cliffline there are glacial and fluvioglacial deposits, and these are dropping down onto the foreshore bit by bit as the coast retreats. The process is slow, but inexorable, and is essentially one of sudden or catastrophic cliff collapses in different locations as one big tree after another comes down-- usually during an extreme storm event like Storm Ophelia or Storm Brian in recent weeks.  A huge oak tree came down close to Picton Ferry during one or the other of those storms.

This tree will be down before too long, and when it falls a chunk of the 
cliff face will come with it.

(As it happens, similar processes have been at work at Craig Rhosyfelin, dislodging large blocks of rhyolite at irregular intervals and causing fallen and smashed-up rock debris to accumulate against the rock face.  There, however, the trees may have always been much smaller.)

Annotated image from the Geology of Britain Viewer (BGS).  Here we can see that glacial deposits are quite abundant in this area.

Erratics are scattered on the foreshore to the east of Picton Point, but they are far more numerous on the western side.  Most of them are less than 50 cms in diameter.  They are rather well rounded, and heavily stained.  This suggests two things to me -- one, that they have come from fluvioglacial sands and gravels rather than from till;  and two, that the deposits are old (Anglian or Wolstonian) rather than Devensian.

Two images from the foreshore to the west of Picton Point. Most of the rock fragments are quite angular, having come from recent rockfalls on the retreating cliffline; they are mostly Coal Measures sandstones.  But the rounded cobbles include rhyolite, dolerite, gabbro, volcanic ash, and Cambrian sandstones -- almost certainly from the St David's Peninsula

These are early days in my Picton Point investigations -- watch this space.....

Sunday, 29 October 2017

The Carn Meini mystery

Carn Meini, as we all know, is the place where it all started........ this set of four craggy outcrops of dolerite on the crest of the Preseli ridge was identified by HH Thomas back in 1921 as the place from which many of the spotted dolerites at Stonehenge had come.  He didn't think there was a quarry there, but Richard Atkinson did, and since the 1950's it has of course been promoted heavily by EH and Uncle Tom Cobbley and all as THE Neolithic quarrying site.  This idea was pushed very recently by Tim Darvill and the late Geoffrey Wainwright in their big chapter in the Pembrokeshire County History, even though the geologists now seem to be agreed that none of the spotted dolerites at Stonehenge actually came from here.  As they say, you don't want the truth to get in the way of a good story.......

For good measure, TD and GW were intent upon making the place even more famous, and in the literature it is now promoted as having the earliest stone quarry in the British Isles -- dating from the Mesolithic -- where "meta-mudstones" were extracted for reasons unknown.  Then there is that funny little enclosure, which TD and GW promoted as a sort of protective barrier to stop the locals from pinching valuable bluestones from the quarrying storage depot.  So there is quite a story there, which you can believe or poke fun at, as the case may be......

Now then.  We have a problem about the name.  "Carn Meini" means "stony crag".  On the older maps the locality is shown as "Carn Meini" or "Carn Menyn" more or less interchangeably -- but Carn Menyn is the preferred spelling on the modern OS maps.  That's a bit of a nonsense name, since "menyn" means "butter" -- and how can you name a craggy rock after a lump of butter?  Bertie Charles, in his book on the place names of Pembrokeshire, explains this as an indication of a fertile upland grazing area that ran up to the rocks, maybe involving cattle grazing and butter making in a "hafod" or summer settlement.  There is indeed a trace of a ruined dwelling with small enclosures about a kilometre from the rocks, and another just 500m from the rocks.

Was there a cottage here, where cattle were looked after on their summer grazing area, 
and where butter was made?

But then it gets interesting.  Last night I was reading the classic local history of Mynachlog-ddu parish, by ET Lewis.  With very rare exceptions, he refers to the rocks not as Carn Meini but as CAERMEINI.  In doing that, he must have been representing local verbal usage of the name, and he cites a lot of documentary evidence as well.  He was a fluent Welsh speaker, and he would not have confused "carn" with "caer".  The word means a fort, castle or citadel -- or some defended and strengthened place.  Interestingly enough, the three closest farms are Caermeini Isaf (lower), Ganol (middle) and Uchaf (upper) -- and those spellings are used on the current OS maps. Sometimes descriptive words are used in a picturesque sense (eg "castell" or "castle" is used for a crag that looks particularly romantic or ruinous!) but Lewis clearly did not think that this was the case here.  So we have a tradition locally of a fortified site at Carn Meini or Caer Meini...........

Lewis also mentions the local Welsh dialect in the Mynachlog-ddu area, in which the word "mynydd" (mountain) is pronounced "mini" -- so he infers that both "meini" and "menyn" might just be corruptions of the word for "mountain".   So the meaning might be "mountain fort" or "mountain crag" -- ie nothing to do with butter.

So here is an interesting thought -- could it be that there was a defended structure on Carn Meni which features in local traditions and local place names?  Is the "walled" enclosure described by Darvill and Wainwright a candidate?  It really is a pathetic little feature which can never have been very prominent, but who knows?

Now it gets even more interesting.  ET Lewis has a theory that the flattish plateau area above Talfynydd was the site of the Battle of Mynydd Carn in 1081, in which the forces of Rhys ap Tewdwr and Gruffydd ap Cynan (th princes of Gwynedd and Deheubarth) were involved in a terrible conflict, with huge slaughter, with the armies of the princes of Powys and Morgannwg.  Rhys and Gruffydd marched eastwards for a long day from St Davids, and Lewis thought that they marched along the old Golden Road on the Preseli ridge to meet the foe.  When they arrived in the vicinity of Talfynydd (just over 1 km west of Carn Meini) the armies of the princes of Powys and Morgannwg had already been in residence in the vicinity for about three weeks.  Could it be that that they had established their camp around the Carn Meini crags?  And could it be that the princes themselves had established their HQ in the "enclosure",  demarcated by a rough wall which could have been built in a day or two by a group of soldiers with nothing much else to do while they waited for battle?

Darvill and Wainwright were unable to establish that the "wall" had anything to do with quarrying, and did not demonstrate that it was a Neolithic or Bronze Age feature. I think it might have been built in prehistoric times as part of a simple animal enclosure -- but I am more and more attracted by the idea that it might not be prehistoric at all, but was built by some bored soldiers in the year 1081.

Maiden Castle near Trefgarn -- a tumbledown and very delicate tor which was presumably named because it looked like a ruined castle.

Saturday, 28 October 2017

On the redistribution of bluestone erratics

In the light of my previous post, on the "bluestone erratic train", I have been re-reading this interesting paper by Phil Gibbard et al:

New insights into the Quaternary evolution of the Bristol Channel, UK
ISSN 0267-8179.
DOI: 10.1002/jqs.2951

I covered it briefly in a previous post, here:

It's great to see that things are moving (so to speak) in the Bristol Channel arena at last, and a number of geomorphologists are realising that hereabouts we will find information crucial to our understanding of the Quaternary of south-west Britain.  Sounds obvious -- so it's all the more surprising that the area has been relatively neglected while research has been concentrated in other areas like north Wales, eastern England and the fringes of Scotland. 

For many years it has been known that during the Late Devensian glacial episode, ice from the South Wales outlet glaciers pushed across the coast in three main areas -- Carmarthen Bay (the Tywi Glacier), Swansea Bay (the Tawe and Neath Valley glaciers) and in the Cardiff-Newport area (the (Taf and Rhondda Glaciers).  The Usk Glacier is not thought to have reached the coast.  Most of the work on these features, as described by Prof David Bowen and others, has been land-based, and is summarised on this map:

A lot of work is now becoming available in the literature relating to the Bristol Channel sediments and bedforms, as repeated in other posts on this blog.  This is suggesting that Devensian ice did cross the coast around Cardiff and Newport, and that the above map needs to be corrected in that respect.  And the evidence for the inner and outer moraines in Swansea Bay is truly spectacular, as shown in the map at the head of this post, taken from the Gibbard et al paper.

What this all means is that any bluestone erratic train running between Preseli and Salisbury Plain would have been effectively disrupted or smashed to pieces by these Devensian advances involving ice from the Welsh ice cap, flowing broadly southwards from the Brecon Beacons and the uplands of the South Wales Coalfield. 

Here is another map from Gibbard et al, with my hypothetical bluestone erratics train superimposed upon it.

So if anybody asks me in future why there is no trail or train of large bluestone erratics running all the way from Preseli to Stonehenge, I will show them this map.  It demonstrates that there is NOWHERE in South Wales where the erratic train could have survived intact -- in an unmodified form.  In Carmarthen Bay, Swansea Bay and the Cardiff-Newport area old Irish Sea Glacier erratics might well have been flushed out beyond the present coastline.  In other areas any erratics lying about will have been incorporated and reworked into Devensian morainic deposits.  The erratics will still be there -- somewhere, and probably buried -- but the chances of finding them will be infinitesimally small.  In fact pre-Devensian glacial deposits are also very difficult to find in Glamorgan; we only know of one substantial survival, at Pencoed.

So that leaves two areas where we might find erratics -- immediately to the south of Preseli and in Somerset and Avon.  In the latter area, as we all know, no big bluestone erratics (demonstrably from Pembrokeshire) are known apart from those at Stonehenge.  But in eastern Pembrokeshire, down-glacier from the Preseli Hills, there are abundant bluestone erratics, as noticed by Thomas, Griffiths and other researchers.

By the way, ALL of the glacial limits on the above map are speculative.  I have argued over and again that the Late Devensian limit shown does not make any sense and I don't know why researchers keep on showing it on maps when it defies all the rules of glacier behaviour.  And the Early / Middle Devensian limit is even more controversial --  I'll report soon on a new paper that demonstrates that the assumed glacial episode at that time is just as fanciful as a bluestone quarry. (My words, not theirs.......)

Friday, 27 October 2017

The Bluestones Erratic Train

Over the years we have discussed erratic trains and trails on many occasions, and I have just prepared a new map showing the main ice streams affecting the Bristol Channel area in the Anglian Glaciation.  (Or maybe it was the Wolstonian?  Nothing is certain in this life......)

I'm fairly happy with the ice stream arrows for both the Irish Sea Glacier and the Welsh outlet glaciers affecting South Wales.  The red arrow is based on the paper I did with Lionel Jackson in 2009 in "Earth" magazine, suggesting a contact zone along which the two ice masses ran side by side at more or less the same speed, without much mingling.  (Ice acts in some ways like a fluid, but we must not carry that analogy too far.....)

Along the red line we might expect to find a train of bluestone erratics, but only if there was a continuous process of erosion and entrainment at the Presell end of the line, in the source area. As I have explained, I think the entrainment of Preseli erratics (spotted and unspotted dolerites, rhyolites, dacites, volcanic ashes and sandstones) might only have occurred on a substantial scale at the beginning of the glaciation concerned, with the supply cut off as the ice thickened.  So the route might be approximately OK, but the "erratic train" might just be a pipe dream.

There would also have been wobbles in the route, and in reality the "red route" would have had a lot of kinks in it, in response to waxing and waning ice pressure both from the southern flank and the northern one.

Then there comes the last complication -- the wastage of the Irish Sea Glacier, which would probably have been catastrophic and very rapid.  It appears to be normal towards the end of a glacial episode for "pulses" or readvances to occur around the fringes of smaller ice masses such as the Welsh ice cap -- and advances of the South Wales glaciers could well have pushed the debris associated with the Irish Sea Glacier (including quantities of erratics) southwards, beyond the present coast line and into the area now submerged beneath the sea.  There are signs of just such terminal and lateral moraines both in Swansea Bay and in Cardigan Bay, associated with Devonian glacier advances following Irish sea ice wastage.

More to be discovered -- of that I have no doubt.