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....
To order, click
HERE

Tuesday, 22 August 2017

Erratics from Newport beach

There have been some very low tides recently, and on a walk the other day I found a large exposure of rounded pebbles on an outcrop of till, very close to the outermost end of the river channel.  This was very close to the old Lifeboat Station at Cwm.  These pebbles are clearly derived from the till, but the rounding is modern -- every now and again this area is exposed and subjected to quite violent wave action.  This is a photo of some of the pebbles collected:


The bulk of the pebbles exposed just now are sandstones, gritstone and shales -- many of these are typical of the Ordovician sediments in this general area, and from the eastern part of Cardigan Bay -- in Ceredigion.  But there are a lot of these igneous pebbles too, which I refer to as porphyritic volcanics, and they sure as eggs are not local.  To my untrained eye they look as if they might have come from the Ramsey Island volcanic outcrops, but an origin there is very unlikely -- so I suggest that they have come from either the Harlech Dome, from the Snowdon volcanic zone, or maybe even from the Lake District.   Maybe from all of these areas...........

I'm intrigued by how similar this assortment is to the pebbles which Sid Howells is looking at from Flat Holm.  Some of those, of course, COULD have come from Ramsey Island, since an origin there would accord with what we know about directions of ice movement.

This is a photo which I published earlier, of some of the Flat Holm erratic pebbles:


All advice on what these latest pebbles from Newport are, and where they might have come from, gratefully received.......

Monday, 21 August 2017

Multiple bluestone rock types -- but how many provenances?



In January 2015 Myris said that the geologists accept around 10 different rock types in the bluestone assemblage.  But the number of rock types is self-evidently not a guide to the number of provenances. 

The dolerites, for example, which some might wish to count as belonging to a single rock type, have almost certainly come from multiple locations -- the samples reported on are all different, suggesting that they have NOT all come from the same place.  The same is true of the "rhyolites with fabric" -- one rock type maybe, but three different groups according to the analysis. So there are three (at least) different provenances for that rock type alone.  The same is true of the sandstones -- they are all sandstones, but of different ages and from three different places.

See also:
https://brian-mountainman.blogspot.co.uk/2014/08/the-vexed-question-of-stonehenge-stones.html 
https://brian-mountainman.blogspot.co.uk/2010/11/more-than-30-different-bluestone.html
https://brian-mountainman.blogspot.co.uk/2016/05/talk-to-chartered-institute-for.html

Here we go again, with an update of the list published in January 2015.  Maybe this will all become clearer with the publication of a new popular paper by Ixer and Bevins in Geology Today, in the autumn. There are at least 18 different rock types, and probably more than 20. That means multiple provenances, exactly as you would expect with a collection of glacial erratics.

** There are 31 dolerite orthostats, of which 14 were sampled in 1991 and 2008.  Some are standing stones and some are stumps.  Some are spotted and some are unspotted.  The spots are now thought to be not felspars but aggregations or clusters of low grade, secondary metamorphic minerals.

Bevins, Ixer and Pearce (2014) analysed 22 Stonehenge dolerite samples, and suggested that they were clustered into three groups, with one sample petrologically distinct from all three.  So there are three groups and one outlier -- four types. Every one of the 22 samples is unique, and the possibility must be entertained that every one has come from a different geographical location in eastern Preseli.

** There are four above-ground volcanic rocks in the orthostat collection (stones 38, 40, 46 and 48).  There seem to be four distinct types - two dacites and two rhyolites.  They are referred to by the geologists as rhyolitic tuffs, foliated rhyolitic tuffs, crystal-lithic-vitric tuffs, and argillaceous tuffs.  They have come from four different north Pembrokeshire locations. Stone 38 has an unusual mineralogy including graphitising carbon.  

** There is not much debris to match the 4 volcanic rock orthostats in the Stonehenge debitage, but similar fragments are found in the great cursus field.  In the debitage, unique volcanic material has been classified as belonging to two types -- Volcanic Group A and Volcanic group B.  None of the potential parent orthostats for Volcanic Group A (32c, 33e, 33f, 40c and 41d) have been petrographically examined, making it impossible to relate this debitage to any (or all) of the buried stones.  Ixer and Bevins (2016) say: ".........on present knowledge the origin(s) of the Volcanic Group A lithics is still expected to be found within the Ordovician volcanic sequences in the north Pembrokeshire area on the northern side of the Mynydd Preseli range probably amongst those outcrops examined by Evans (1945)."

** There are two micaceous sandstone stumps -- numbered 40g and 42c.  There are also lumps of Lower Palaeozoic sandstone scattered about in the debitage -- the largest lump weighs c 8.5 kg.  There appear to be two types, with possible sources in the Lower Palaeozoic rocks of north-west Pembrokeshire.

** The Altar Stone (stone 80) is a greenish calcareous sandstone, probably from the Senni Beds of Carmarthenshire or Powys. (It is not from Milford Haven.)  So just one rock type here. There is some debitage related to this stone, but it cannot be established that the fragments came from the Altar Stone itself (Ixer and Bevins, 2013).  The most feasible provenance for the stone is the Laugharne - Craig Ddu -- Llansteffan area of Carmerthenshire.

** In the debitage there are many fragments of rhyolites, some with planar fabrics -- and most matching closely (but not perfectly) the rock outcrops at Craig Rhosyfelin.  There appear to be three distinct groups of "rhyolites with fabric", all assumed to have come from the Pont Saeson area.  There may be a match with orthostat 32e or 32d (Ixer and Bevins, 2011), but the debris analyses does not match any of the known volcanic orthostats.

** There are also some basic tuffs in the collection of fragments from the debitage -- two lithologically different types (Ixer and Bevins, 2013). These are probably also from the Fishguard Volcanic Series.

** Other lithics in the stone collections from the debitage (eg. haematite (from the Reading Beds?), greensand, slate, limestones, Mesozoic sandstones and gabbros) appear genuine, and need further research.

To sum up: 

Ixer and Bevins (2014) state that there are “about ten types of bluestone” represented in the orthostat / debitage samples, but they also show that these have nonetheless come from at least 20 different locations.  It is estimated on the basis of the above points that there are at least 30 different rock types represented in the full "bluestone assemblage" -- especially when due respect is given in this count to cobbles as well as orthostats and flakes, for reasons frequently recited on this blog. 

It should also be noted that the majority of the 43 bluestone monoliths/stumps at Stonehenge have still not been sampled and analysed.  The new work reinforces the idea that the Stonehenge bluestone assemblage is made up entirely of rock types from the west, and that they have come mostly from north Pembrokeshire. 


Finally, a plea to the geologists -- if there is anything wrong with this list, please tell us about it, and give us your corrections and citations.  As ever, I'll publish them without fear or favour!

Friday, 18 August 2017

Horrid Happenings at Rhosyfelin


This is from the Oriel y Parc Facebook page, advertising a storytelling session which I have promised for them next week.  Goodness knows why they chose this pic of me at the Old Ruin.  Nothing to do with me.  That got me thinking.  Since I am supposed to be telling terrible tales and horrible histories and fantastical fables, I need the advice of experts.

Tell me, should I tell the terrible tale of the hairy monster who comes out of the dark woods to dig deep holes in the ground at Rhosyfelin, every year at the time of the harvest moon?  The kids could probably cope with it, but would it all be too scary for adults of a sensitive disposition?

Thursday, 17 August 2017

Bluestone recycling


What were we saying about the re-use of bluestones in many different setting at the old ruin?  Note that the artist has even accurately portrayed the many different bluestone lithologies..........

Wednesday, 16 August 2017

Spats are as old as the hills.......


Geologist and physician Henry Hicks, a good Pembrokeshire man who 
did not suffer fools lightly.

Sometimes one wonders whether our little academic spats demonstrate a lowering of academic standards, or a reduction in tolerance, or a sort of hypersensitivity on the part of researchers.  Surely it cannot have been so bad in the good old days?  Well, it's reassuring to know that it was just as bad, if not worse.......

Here is short extract from Geol Mag 1886, involving Henry Hicks (who seems to have been a crusty sort of fellow) and a certain Prof Hughes, who clearly had a habit of expressing strong views on places he had not actually visited and things he knew nothing about.........

Geol Mag Volume 3, Issue 12
December 1886 , pp. 566-571
V.—On the Ffynnon Beuno and Cae Gwyn Caves

Henry Hicks

DOI: https://doi.org/10.1017/S0016756800466926
Published online: 01 May 2009

Abstract

The best reply that I can make to Prof. Hughes’ remarks, in the Geological Magazine for November, on the Ffynnon Beuno Caves, is to publish the substance of the report presented to the British Association, especially as an opportunity will be given to those interested in the inquiry to examine the section during the further explorations to be carried on, probably in the month of June next year. Some of his statements—especially as regards the position of the fence, which is entirely at the opposite end of the cavern to that at which the flint flake was found, also as to the position of the flake, and. the nature of the deposits overlying it—are so entirely misleading, that I can only account for such statements being made by the fact that Prof. Hughes did not visit the section, though strongly urged by me to do so, until it had been almost entirely covered over, and work for the time suspended, and by his hasty survey of the surrounding conditions.

Erratic blocks of England and Wales



Thanks to Rob for drawing my attention to this wonderful article and map.  I had never seen this info before.  It has come to the surface thanks to the great project under way in the Birmingham area, in which Rob and Prof Ian Fairchild are involved.

Look at the date of this work: 1878.  That's rather a long time ago.  But our Victorian ancestors were great field workers and often pretty good geologists too -- even though their ideas on glaciation were rather primitive, to say the least.  No matter -- the observations formed the foundations of much of the glacial history as we understand it today, and the maps are classics of their kind.

I particularly love this bit:  "There are probably many boulders which I have not yet seen, and the positions of which, therefore, are not shown in the map."  Quite so.

--------------

Thanks to the wonders of OCR, here is a transcript of part of the paper:


ERRATIC BLOCKS OF ENGLAND AND WALES. p 425

RESULTS of a Systematic SURVEY, in 1878, of the DIRECTIONS and Limits of DISPERSION, MODE of OCCURRENCE,and RELATION to DRIFT-DEP0SlTS of the ERRATIC BLOCKS or BOULDERS of the West of ENGLAND and East of WALES, including  a REVISlON of many Years' previous 0BSERVATIONS.

By D. MACKINT0SH, Esq., F.G.S. (Read March 26, 1879.)


Extract
IX. :EXPLANATION OF MAP, PLATE XXlI.

As it is impossible to ascertain the precise routes taken by boulders, in a map it is perhaps least presumptuous to draw straight or slightly curved lines from their sources to their terminations. As most of the Kirkcudbrightshire granite blocks would appear to have been dispersed from Criffel mountain or the neighbourhood, to prevent complication I have represented that mountain as the centre of dispersion. The barrier offered by the westerly extension of the Cumberland mountains renders it necessary to assume a curve in the route taken by these boulders. As I have already described the Shapfell granite dispersion (see Geol. Mag. for Aug. 1870 ; and Quart. Journ. Geol. Soc. for Aug. 1873), and as it has been made the subject of papers by other authors, I have only mentioned it in the map. For the same reason the stream of large limestone boulders found along the east coast of Morecambe Bay is merely mentioned. The boulders of Silurian grit, felstone, &c. which went south from the mountain-front of Westmoreland are merely mentioned, as it is not certain that many of them found their way further south than Morecambe :Bay. The "greenstone" boulders are not inserted in the map. As the Arenig boulders which are believed to have wandered as far south as the neighbourhood of Bromsgrove would appear to have gone first in an easterly direction, it is obviously necessary that a curved route should be assigned to them in the middle part of their course. There are probably many boulders which I have not yet seen, and the positions of which, therefore, are not shown in the map.

An attempt to map the positions and courses of boulders is justified by the fact that most of them have been found more or less imbedded in clay or gravel, at all angles, often standing on end - in other words, in the positions in which they were left by the ice which carried them during the Glacial period.

Tuesday, 15 August 2017

Just see how the jolly bandwaggon rolls..........


 Image:  Colby College


I thought that with the departure of Phil Bennett, some common sense might break out in Pembs Coast National Park HQ, and that there might be rather more respect for the facts. Fat chance.  The opportunity of turning a dishonest quid or few has proved too tempting to miss, so here we go again.  The usual nonsense in the blurb, in spite of endless requests from me to moderate the purple prose. A guided bus tour on 20th Sept, at the end of the digging season, led by MPP himself, complete with barbecued burgers just as they used to be in the good ol' days at the Durrington raves. 

Then the usual evening talk at 7.30, for the ears of the faithful.   Title: The Welsh Origins of Stonehenge.  Depressing, isn't it?

If you want to join the whole rave, it will set you back almost £40. I think I might give it a miss.......

http://www.pembrokeshirecoast.org.uk/default.asp?PID=367&EO=2520

Monday, 14 August 2017

The strange blacked-out world of the archaeologist....


Now here is an interesting question.  Do archaeologists always wander about in the countryside with boxes on their heads?

I have been thumbing through a few of my books looking for some info, when I came upon a page or two in Prof Mike Parker-Pearson's big book on Stonehenge which left me gobsmacked.  OK --I have read it all before, but now it has struck me ever more forcibly that certain senior archaeologists know absolutely nothing about the forces that have affected the landscape.  For them, geomorphology is just a long word with an unknown meaning.

On p 289 MPP is seeking to flag up the wondrous routes available to our Neolithic ancestors who wanted to carry all those lovely bluestones across country all the way to Stonehenge.  He refers to "potentially excellent transport links" and goes on to say:  "The glaciated valleys of Preseli have U-shaped profiles, with wide, flat, stone-free bottoms.  There is plenty of room for moving megaliths along a valley bottom without having to negotiate its stream....."

Don't lets mince words here.  This is complete and utter nonsense.  Which landscape has MPP actually been looking at?  There are no glacial troughs / glaciated valleys with flat bottoms in Pembrokshire.  I repeat.   THERE ARE NO GLACIAL TROUGHS IN PEMBROKESHIRE.  He must have been reading some ancient text book or other, and got all confused.  The topography is all wrong for glacial troughs, and this was an area of areal scouring, not concentrated ice flow.    There are no U-shaped profiles and no wide, flat, stone-free valley bottoms.

What we do have are a number of spectacular sub-glacial meltwater channels, especially in western Preseli, including Cwm Gwaun which MPP knows very well since that's where Bessie's pub is located.  These valleys do have wide flattish floors, but they are by no means stone free.  And these valleys are of no use for the bearers of large stones, since they are all to the WEST of the territory in which MPP keeps on seeing Neolithic quarries.  These latter so-called quarry sites are in EASTERN Preseli, from which he wants the stones to be transported EASTWARDS.

He then goes on to talk of the Nevern Valley as one of the "hotspots of Britain's Early Neolithic."  That again, if I may say so, is unsupported by the evidence.  There is a little group of portal dolmens in and around the valley, but the density of features is no greater than anywhere else in West Wales, and it is fanciful in the extreme to refer to it as a cultural "hotspot".

Then he goes on to talk of the valley sides being densely wooded and the valley floors being more easy to move about on.  "These wide-bottomed valleys would have formed ideal droveways for taking the cattle on to the high pastures, past Craig Rhosyfelin and on to Waun Mawn and Carn Goedog." (p 289)   That again is complete nonsense. For a start, there is nothing whatsoever to link these named sites apart from MPP's fertile imagination.  Secondly, all the evidence that I have seen suggests that the valley floors were just as densely wooded as the valley sides in the Neolithic -- and maybe even more difficult to move about on, given that they would have contained many boggy areas and pools on those parts of the valley floor where gradients were low.  Look at Esgyrn Bottom, Criney, Cwm Gwaun and the Brynberian Valley even today, after centuries of land clearance and land drainage..........

I sometimes despair, but must press on.....

Quickly on to page 290.  "Recent archaeological investigations in advance of new pipelines have found evidence of many Neolithic sites in south Wales' valleys...."  He cites Louise Austin as his source on this, but I wonder what she really thinks?  It's news to me.  All of the distribution maps for Neolithic features in South Wales show that our Neolithic ancestors avoided river valleys like the plague -- they always settled and built their structures on interfluves, upland swells, dryish areas on hilltops and on promontories where visibility was good and where waterlogging was not a problem.

Quote:  "Neolithic traders would have used these glaciated valleys not only to avoid the thickly wooded hillsides but also to pass through the many settlements.  The principal routeways would have followed the valleys such as the Taf, the Towey (sic) and the Usk.  These flat-bottomed valleys were the Neolithic equivalent of the motorways, cleared of forest by the earliest Neolithic farmers and facilitating long-distance movement of people and their goods.  For the movers of bluestones, the route was relatively straightforward..........."  And so on and so on.  The Neolithic motorway bit is quite wonderful, thrown in there for the delectation of journalists and others with vivid imaginations.

Who says that the flat-bottomed valleys were cleared of forest in the Early Neolithic? I know of no evidence to support this contention.   Darvill and Wainwright, in the recent Pembrokeshire County History chapter, do not refer to any process of valley floor woodland clearance in the pre-metal period.  There was very little settled farming at the time; clearances were ephemeral, with slash and burn being used here and there in the forest by people who kept moving.  And why would they want to clear valley floors, at a time when forests held valuable resources in a hunter / gatherer society?  The valleys may have been used for shelter, to get away from the wind and the rain, and it was always far easier to move animals in the uplands, where the forests would have been more scrubby and intermittent.  If there were "droving" movement routes, they would have been on the interfluves and plateaux, not on the valley floors.

I have been looking up the literature by Mike Walker, John Evans, Martin Bell and others to see whether there is evidence of extensive valley floor forest clearance in West Wales in the Early Neolithic, around 5,000 yrs BP.  As far as I can see, there is none.  The Elm Decline is much debated, and there are traces of it in West Wales,  but land clearance associated with permanent settlement and agriculture in West Wales came much later.  I have described what the valleys probably looked like here:

https://brian-mountainman.blogspot.co.uk/2016/11/brynberian-gorge-paradise-for-neolithic.html

I sometimes despair at the apparently infinite capacity of certain archaeologists simply to invent evidence where there is none.  That is scientifically reprehensible, and people who invent evidence should be hauled before the Inquisition and charged with scientific fraud.  Having been found guilty, they should be cast into everlasting darkness, well away from Bessie's pub.  Why do their peers put up with it?  Will they ever change?  Not in West Wales, I suspect.  They are in too deep.

But it would help if every now and then they could take those cardboard boxes off their heads, read a good geomorphology textbook, and start looking at the landscape.

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

PS.  Here is an additional source -- from Nikki Cook, in Pembs Hist Soc Journal, 2006:
 
"Although the Neolithic is generally thought to be the time of the first farmers, it is highly likely that to start with people still lived a fairly nomadic lifestyle, moving between upland and lowland pastures herding animals. As a result the evidence we have for actual settlements is quite scanty when compared with that for ritual/funerary monuments.  It is clear that people in the Neolithic possessed the ability to build lasting architectural forms, as evidenced by the numerous chambered tombs seen within Pembrokeshire, but their lifestyle meant they had no need to build lasting domestic dwellings.






Tuesday, 1 August 2017

Areal scouring on the Pembrokeshire islands



Here are two more of Paul Davies's fabulous images from the Pembs Geology Group Facebook page.  Click to enlarge-- the detail is truly impressive!

The top photo shows Skokholm and the bottom Skomer -- both off the south Pembrokeshire coast.

The pics show just how heavily scoured these island landscapes are -- there are occasional erratics, but real glacial deposits are hard to find (that having been said, they are hard to search for too, since these are nature reserves with nesting seabirds everywhere, so one is not encouraged to scrabble about on the clifftops, where till exposures might be found.........).

The last occasion on which ice passed over these islands was the Late Devensian, around 20,000 years ago, but maybe they have been scoured and abraded on three separate occasions during the Quaternary.

Monday, 31 July 2017

Westdale Bay and the meltwater channel


This is a fabulous image taken by Paul Davies and published on the Pembrokeshire Geology Group Facebook page.  Click to enlarge.

In the background we can see the Milford Haven waterway.  The valley which we can see cutting across the neck of Dale Peninsula is almost certainly a meltwater channel of considerable age.  It may well be the same age (Anglian Glaciation?) as the other big subglacial channels of north Pembrokeshire. It is rather a spectacular feature -- I have never seen it so clearly illustrated in a photo.  The channel runs along the line of the very important Ritec Fault, which "guides" many major features, including the alignment of Milford Haven itself.  The brecciated zone which is often associated with major faulting is easily picket out by fluvial and glacial processes over a very long period of time.

The "plug" of Pleistocene deposits which partly fills the valley is very obvious -- see other posts on this by putting "Westdale"into the search box. I think these deposits are of Devensian age, around 20,000 years old.

Some researchers have suggested that the Dale Peninsula was once an island, and that a narrow strait ran along the course of this valley.  That's possible, but I am not sure the valley is deep enough for that.  I would like to see some evidence of old sea cliffs and maybe beach deposits well into the valley and beneath the glacial / periglacial sediments.  Such deposits could only be found through drilling..............

For the moment, I prefer to think of the valley as a Pleistocene deepening of an old fault-guided river valley.  As I have indicated elsewhere, there are other signs of meltwater erosion in this part of Pembrokeshire, and of course the classic kame terrace not far away, at Mullock Bridge.

Saturday, 29 July 2017

Bluestone pillars or boulders?




I have no idea (well, actually I do) why EH and almost everybody else insists on portraying the bluestone circle at Stonehenge as if it was a circle of slim and elegant pillars.  The evidence for that is extremely scanty, as I keep on saying whenever I am in party pooper mode.

The pic above is from the EH display at the Stonehenge Visitor Centre.

Actually, as we now know from the excellent "Stones of Stonehenge" project (the Simon Banton one, not the MPP one), the bluestones were a mottley collection of heavily abraded slabs, stumps and boulders -- as fine a collection of glacial erratics as you are ever likely to find anywhere.

http://www.stonesofstonehenge.org.uk/search/label/Bluestone 

I accept that elongated pillars of spotted delerite were preferentially used in the final setting of stones in the bluestone horseshoe.

If you want a more accurate representation of what the bluestone circle might have looked like (forget for a moment about the sarsens) this pic from Moel Ty Uchaf is a rather nice guide.




Both sides of the argument....

This is the English-language page from the Pembs Coast National Park's tourist newspaper which deals with the bluestone quarrying debate.  I have been badgering them for years to stop trotting out the fantasies of the senior archaeologists and to accept that there is a debate going on -- in which there is room for some science too!  Anyway, to their credit they responded, and invited Geoff Wainwright and me to contribute short bits of text. This is the result.  Sadly, Geoff died before this edition of "Coast to Coast" was published.




Friday, 21 July 2017

Yet more BBC nonsense on Stonehenge



No sooner have I finished one gripe about the BBC  than along comes another absurd non-story from the corporation, and yet another piece of Stonehenge mythologisation.  Will it never end?

http://www.bbc.com/travel/story/20170713-why-stonehenge-was-built

This time, in addition to the usual guff about Stonehenge breakthroughs and new exciting discoveries, Vince Gaffney and Mike Parker Pearson are the featured archaeologists. There is nothing new -- this is just old info, regurgitated for no particular reason.  Somebody presumably needed to make a programme about Stonehenge.   In the midst of all the purple prose, Vince Gaffney makes one rather nice statement arising out of the fiasco surrounding the stones that never were, at Durrington Walls:  “Following this survey, we know not only where things are but where they aren’t as well.”  Quite so.

MPP's standard bluestone story is repeated here yet again.  Quote:  Parker Pearson suggests that the Welsh bluestones were the first to be put in place at Stonehenge, and that it was the monument that they came from that was important. The stones would have been considered to be ancestral symbols of western Britons, he said, and “bringing them to Salisbury Plain was an act of unification of the two main Neolithic peoples of southern Britain.”  Even today, the Preseli hills are dotted with dolmens (ancient tombs). “The density of dolmens reveals that this was an important region (both politically and spiritually) some 700 years before Stonehenge,” Parker Pearson said, making it “possibly a leading territory within western Britain in the centuries before 3000 BC.”  But even if we agree with the theory that bringing the stones from Wales was a symbolic and even political, act, it presents another mystery: how did prehistoric Britons move those huge stones?
Some suggest that people didn’t move the stones at all, and that instead, glaciers transported the stones across southern Britain. But the finding of two ancient stone quarries in Preseli ended that debate for the most part.  Scientists also have experimented with ideas of how to transport the large stones 160 miles (260km) from Wales. According to Parker Pearson, they discovered that moving small megaliths like the bluestones, which mostly weighed 2 tons or less, was not actually that difficult – even with just dragging the stone on a sledge."

Leaving aside the "ancient stone quarries" for the moment, I wonder why MPP needs to mislead gullible reporters (and a gullible TV public) by giving false information about the density of dolmens in the Preseli Hills?  It is quite clear from the maps of prehistoric features in West Wales (see the Darvill /Wainwright chapter in the Pembs County History) that dolmens are NOT that abundant in the Preseli Hills, and that the density of these and related features is much greater in other parts of Pembrokeshire.   What the hell -- when there is a good story to tell, who cares about the truth?

And moving bluestone monoliths is not that difficult?   Sure it's not, in a London Park on a sunny day with lots of willing students to pull a sledge across a nice flat lawn......

Everything is twisted -- and these senior archaeologists will continue to twist things for as long as they are allowed to get away with it.



Wednesday, 19 July 2017

More on Stonehenge mental health healing project



I hadn't realised it, but there was a BBC Radio 4 "Open Country" broadcast back in April, which can still be listened to here:

http://www.bbc.co.uk/programmes/b08md98n

One has to feel positive about the effects of the experience on the participants who needed help.  And it is great to hear the views of those who previously felt isolated and fearful of social contacts.  Parts of the 24 min programme are genuinely moving, and the "bonding" of those who took part in the 10 week courses in the Stonehenge landscape was clearly quite substantial.  The programme concentrated on the last day of the course as experienced by one of the groups -- in which the participants were granted access to the centre of the stone circle, where they shouted, sang, cheered and played musical instruments.

Tim Darvill was clearly involved in the course at intervals, and good for him for giving his time so enthusiastically.

And yet ... and yet..... having listened to the programme and having quite positive personal views about the project itself, I still have this rather deep sense of unease.  Tim, when interviewed, gave his familiar version of the Stonehenge bluestone transport story, and talked of Stonehenge as a centre of healing. No ifs, buts or maybes -- this, he said, was the way it was, and because he is such a senior academic we can be pretty sure that those who took part in the course were deeply grateful for being told "the truth" by an experienced academic.  Did Tim explain that his theory about "the healing stones" is actually hotly disputed, and that there are other theories too, some of which have rather more substance to them?  One doubts it....... that would probably have made life too complex for the vulnerable participants to cope with.

So I am now even more convinced that this is yet another episode in the long history of Stonehenge mythologisation.  It's also a nice opportunity for Prof TD to develop the strength of his own "bluestone hospital" theory by saying "Just look what happened to all those unfortunate people who needed help when they came into contact with the stones!  They all felt as if they were healed by the experience!"  I just hope he will never say that -- and my feeling about the BBC interviews is that they showed the immense value of social interaction and "bonding" within a group of vulnerable people brought together regularly over a 10-week period in an ancient landscape, in all weathers, with very careful and sensitive guidance from the project leaders.







Sunday, 16 July 2017

The Bristol Channel Glaciations



There's a very interesting new publication by Gibbard, Hughes and Rolfe which provides fascinating new material on the glaciations of the Bristol Channel - Severn Estuary region.  The authors refer to at least three glacial phases, at least one of which involved a substantial ice incursion into Somerset. Archaeologists, please take note........

Here is the citation:

New insights into the Quaternary evolution of the Bristol Channel, UK
PHILIP L. GIBBARD, PHILIP D. HUGHES and CHRISTOPHER J. ROLFE
JOURNAL OF QUATERNARY SCIENCE (2017)
ISSN 0267-8179.
DOI: 10.1002/jqs.2951
https://www.researchgate.net/publication/318198065

ABSTRACT:
A synthesis of new publically available borehole and bathymetric data, combined with a wealth of
other existing disparate data sources, reveals new insights into the Quaternary history of the Bristol Channel area.  Sediment boreholes throughout the Bristol Channel confirm the area was glaciated in the Pleistocene. Till is present below marine deposits and, in some areas, is visible morphologically as submerged moraines. In the central and eastern Bristol Channel the submerged valley course of the palaeo-Severn is very clear in new high-resolution bathymetric surveys. This former river course and associated tributaries cross-cut through glacial sediments in the Bristol Channel. At least three phases of glaciation are recorded in the Bristol Channel, one related to the southern limits of a Late Devensian Substage ( Marine Isotope Stage (MIS) 2) Welsh Ice Cap which reached into Swansea
Bay, an earlier Devensian (MIS 4–3) glaciation associated with Irish Sea ice, and another older glaciation that is associated with ice that filled the entire outer and central Bristol Channel. The age of the older Bristol Channel glaciation is still open, although it pre-dates the Devensian (Late Pleistocene) and must date to the Middle Pleistocene. It is therefore evident that Pleistocene glacial and fluvial activity, combined with subsequent postglacia sea transgression, directly account for current morphometries of the Bristol Channel and Severn Estuary, and the current geography of the SW British Isles.

 =================

I recommend a reading of this article -- it's written in good plain English, mercifully free of convoluted techno-speak.  Its key findings are interesting, and the authors agree that there was a substantial early glaciation (which has to the the Anglian Glaciation, around 450,000 yrs BP) during which Irish Sea Ice filled the Bristol Channel and the Severn Estuary and flowed into Somerset.  How far the ice travelled to the east is a matter of debate, and so a dashed line is used on their key interpretive map:


 I think the authors could have been a bit braver with this "early glaciation" line, and as suggested many times on this blog, I think the ice at the time of the GBG pressed against the coasts of Devon and Cornwall and pushed south of the Isles of Scilly.

The lobe of ice pushing in over Lundy Island in the early / middle Devensian is to my mind not all that well supported, and is too dependent for comfort upon some cosmogenic dates that might well need correcting. 

I'm also not very keen on the Late Devensian line, shown running south from Milford Haven to the Scilly Isles.  I don't think this is well supported sedimentologically, and it doesn't make glaciological sense either.  I think Late Devensian ice pressed well into the Bristol Channel embayment, and I remain convinced that some of the "pre-Devensian sediments" shown on the map may well prove to be Late Devensian too.

All good fun.  The debate will continue -- but this paper is a welcome addition to the literature.




Thursday, 13 July 2017

The first use of exotic stones on Salisbury Plain



When were bluestones (ie exotic or erratic stones) first used in the Stonehenge landscape?  I asked this question a couple of years ago, and we had a useful discussion following the post.  It can be found here:

https://brian-mountainman.blogspot.se/2015/09/when-were-bluestones-first-used-at.html

This is actually one of the most important questions if we are ever to sort out the question of bluestone transport and use.  The question is still not adequately answered, even though there are now abundant radiocarbon dates associated with stone settings.

As I understand it, there are currently two schools of thought among archaeologists:

1.  According to Mike Parker Pearson bluestones were first placed in the Aubrey Holes at Stonehenge, which means that they were present in the Stonehenge landscape around 3,000 BC or 5,000 BP.  This "early date" might be supported by the presence of fragments of bluestone at the western end of the Cursus -- which was by all accounts earlier than the main phase of building at Stonehenge.

2.  According to Tim Darvill and Geoffrey Wainwright, the bluestones were imported from Wales around 2,500 BC -- 500 years later than the MPP proposal.  That late date is presumably supported if one is sceptical about bluestones in the Aubrey Holes -- and it must be agreed that the evidence of "crushed chalk" at the bottom of one Aubrey Hole is not exactly convincing evidence for a bluestone circle.  Some versions of the story have it that the bluestones were not used until 2,300 BC --  when there was a "new bluestone setting" using stones freshly imported, or else used again following a period of storage in the local bluestone depot.

As I have suggested on this blog, Prof MPP appears to be pushing the "first use" date back and back towards the Early Neolithic, partly in order to accommodate those very inconvenient radiocarbon dates from Rhosyfelin, and partly to tie things in with the "megalithic" phase in West Wales.  This would also of course be supported if the Boles Barrow bluestone really did come from a long barrow that appears to have been constructed around 3,500 BC. (The long barrow building phase on Salisbury Plain is assumed to have been at around the same time as the cromlech / dolmen phase in West Wales.) Also, spotted dolerite ("Preselite") axes apparently dating from the period 4,000 BC - 3,000 BC appear (not very often) in the Stonehenge landscape, and one explanation by Olwen Williams-Thorpe is that they were made close to Stonehenge from in situ erratic material.  That is in my view more likely than the "trading" hypothesis.......

Of course, the earlier the first established use of bluestones can be shown to be, the greater the likelihood that the bluestone erratics were simply used more or less where they were found.  No need for human transport; glacial transport is the obvious and simple explanation.  That's because:

(a) the technology for bluestone transport would simply not have been available before 3,000 BC;
(b) if bluestones were used right at the beginning of the "stone phase" at Stonehenge, that suggests they were collected indiscriminately along with sarsens in the immediate vicinity;
(c) it is vanishingly unlikely that "the bluestone expeditions" would have occurred before the Salisbury Plain tribes had accumulated any skill in the setting of stones into the ground.

As I have said many times before, in the period 3,800 - 3,000 BC, in West Wales, where stones were being used in megalithic structures, those stones were ALWAYS used where found.  No matter what fantasising our archaeological brothers may indulge in, there is no reason why a different set of rules should have applied in the Stonehenge landscape.  Avebury seems to confirm that -- only sarsens were available, and only sarsens were used.

Tuesday, 11 July 2017

Healing at Stonehenge



Thanks to a Current Archaeology reader for drawing my attention to this.  In an article called "A healing journey through the Stonehenge landscape",  in issue 17, Carly Hilts describes an innovative scheme for helping people with mental health issues or emotional problems.  A charity called the Restoration Trust brings people together in a caring environment in the "ancient landscape" of Stonehenge and Salisbury Plain -- with performances, craft activities and mutual support mechanisms designed to provide a sort of "heritage therapy."  The project is dubbed "Human Henge".  So far so good, and of course we wish the organizers ad the participants well.

Bournemouth University is one of many institutions involved, and Tim Darvill is apparently running a complementary research programme.  I wonder what that's all about?  According to the article, TD's ideas about Stonehenge as a "prehistoric Lourdes" are being used -- and the article unquestioningly trots out the usual stuff about the bluestones being quarried in the Preseli Hills, about the proximity of healing springs close to the rock sources,  and "long oral traditions of healing properties." The so-called concentrations of cairns around the springs, and the presence of rock art, are deemed to demonstrate the "special" quality of the local waters -- a quality then transferred to Stonehenge through the transport of monoliths to be used in the construction of Stonehenge.  It's all nonsense, of course, and there is no oral tradition of healing associated with these springs, no greater concentration of cairns than elsewhere, and no greater incidence of rock art. 

Sadly, somebody is inventing evidence here, promoting it through a rather dubious channel (namely the Human Henge project), and misleading some very vulnerable people into the bargain...........

Should one laugh or cry?

Stone's stones and the Cursus connection



I'm very confused about Stone's stones and the Cursus connection. I have been taking another look at this article:

“The petrography, affinity and provenance of lithics from the Cursus Field, Stonehenge”, by RA Ixer & RE Bevins, Wiltshire Archaeological & Natural History Magazine 103 (2010) 1–15

It was published seven years ago, and that's a long time in the great scheme of things relating to Stonehenge. But in it, the authors say that new analyses of rock samples from Stonehenge, the Stonehenge Cursus Field and Pembrokeshire have shown that some of the rhyolite and ash fragments on Salisbury Plain have probably come from innocuous locations between Preseli and the north Pembrokeshire coast, but that others are from unknown locations maybe outside Wales. So far so good.......

Then there is another article by Rob Ixer, :

Digging into Stonehenge’s past
Mineral Planning, issue 143 / October 2012, p 13

www.mineralPlanning.co.uk

In it, he says that the cause (of much new debate) "is a recent re-examination of the contents of a little box of stones collected by JF Stone in 1947 from plough soil close to the Stonehenge Greater Cursus and donated to the Salisbury and South Wiltshire Museum. Many of the ten or so stones – none of which are bigger than a fist – were found to be texturally and mineralogically distinctive.
Initial investigations showed none of these matched any of the standing bluestones......" But Ixer then went on to say that some of them matched the rhyolites from Craig Rhosyfelin, and continued:  "So the contents of a 60-year-old box led to the discovery of the first secure Stonehenge-related quarry site, confirming that man moved the bluestones. But the initial assessment of Stone’s stones was wrong, because in June 2012, one of the rocks was recognised as coming from bluestone SH48, making it only the fourth piece of debitage from thousands investigated that could be matched to a specific bluestone orthostat."

Let's forget the wild speculation about quarries and concentrate on the fragments. Presumably the rocks identified originally as "acid volcanics and tuffs" are now referred to as foliated rhyolites? Is there any spotted dolerite in the collection? And exactly how many different exotic rock types are there in the Stone collection and in other collections from more recent digs at Durrington Walls, Windmill Hill and the Cursus? Did Richard Atkinson really find a lump of spotted dolerite on Silbury Hill, and are there really at least 1300 "bluestone fragments" inside the hill itself?

In an article by Tim Darvill published in 2012, he says:

"A review of samples from the Altar Stone confirmed that it was a fine-to-medium
grained calcareous sandstone of the kind found in the Senni Beds of south Wales.
Four other pieces of sandstone from the Stonehenge Cursus, Stonehenge, Aubrey
Hole 1 and Aubrey Hole 5 share a common lithology as low-grade metasediments
and derive from a different source area, possibly from Lower Palaeozoic sandstone
beds (Ixer & Turner 2006).
"An examination of finds from the Cursus Field collected in 1947 and from
excavations by the SRP in 2006 and 2008 confirmed that much of the material could
be matched with samples from Stonehenge (identified as Groups A–D: Ixer & Bevins
2011a; 2011b) but that some rhyolites could not be matched amongst existing
samples (Ixer & Bevins 2010; Ixer et al. forthcoming)."

(Research activity in the Stonehenge Landscape 2005–2012 Timothy Darvill
Stonehenge and Avebury Revised Research Framework
6 July 2012)

In the recent Darvill / Wainwright chapter in the Pembrokeshire County History (Vol 1), they refer to "widely recognized" rhyolite fragments (some of unknown provenance) in the debitage from the 2008 Stonehenge dig, from the Heelstone area, from some Aubrey Holes, from the Avenue and the Cursus.........

I am rather confused by all of this, because Rob Ixer, in his review of my 2008 book called "The Bluestone Enigma", criticised me for the inaccuracy of my reporting on the finds associated with the Cursus. He said: "Almost every sentence about the Great Cursus and its associated lithics (pp 68, 69, 77, 103, 108) is incorrect -- once again these errors, missing from the original papers, are found on-line." He never did say what those errors were, and I still think that I was reporting accurately on those pages the situation as it was in 2008.

So is there abundant bluestone erratic material in the Stonehenge landscape, or is there not?

Stonehenge and TV garbage


 Image:  BBC / Daily Mail
 
Mike Pitts has been having a go at the latest Stonehenge offering from the Science Channel, which apparently sets new standards in its complete disregard for the facts and its obsession with telling a wacky tale.  I can't bring myself to watch it, but apparently it tries to make the case that executions or murders were conducted at Stonehenge -- and also at other iconic prehistoric sites across Britain -- on the basis that mutilated skeletons are found here and there, at locations that may or may not have anything to do with Stonehenge.  The work cites osteoarchaeologist Jo Buckberry, who must have agreed to be filmed but who clearly had no input into the making of the broadcast programme.

https://mikepitts.wordpress.com/2017/07/10/drowning-in-the-swamp-of-bad-tv-unearthed-at-stonehenge/ 

Jo has commented as follows:

"Ok, so I’ve not seen the to programme. But I gather the editing was, erm, done with artistic licence. These skeletons are from East Yorkshire, not Stonehenge. There is a single burial from Stonehenge of the same date, with very similar injuries. These skeletons were from the 7-10th Century (later Anglo-Saxon), and had evidence of decapitation, but no other injuries. The location and mode of burial, long period of use for the site and evidence of decapitation is suggestive of judicial execution. No idea where they got sacrifices or murders from. How do I know? I analysed and have written 4 papers about them. I was filmed (that’s me in the photo). I talked about a photograph of the Stonehenge skeleton, on a laptop. I’ve never seen the skeleton from Stonehenge…”

Mike Pitts complains about the "stupefying nonsense" trotted out by TV Channels that should know better, and asks: "What is wrong with TV? People are fascinated by Stonehenge. There are extraordinary stories to tell. Why make up such idiocies, insulting your specialists to boot?"

I'll go along with Mike on all of this, but I'll go a great deal further.  He refers to "extraordinary stories" but fails to mention that many of them, accepted gleefully by the archaeology establishment, bear little relation to hard evidence on the ground.  Where is the evidence for bluestone quarrying, or for bluestone transport, or for the use of bluestones at "Bluestonehenge"? 

When last did anybody see a Stonehenge programme which took a properly scientific approach and which laid out theories as working hypotheses instead of "facts"?  When last did any of us see a programme in which the programme makers subjected the archaeologists to proper interrogation or scrutiny?  Over and again on this blog  I have made the point that TV programme makers are partly to blame, in their ongoing obsession with spectacular visuals and narratives that "rewrite prehistory."   But most of the blame for this stream of garbage rests with the archaeologists themselves, some of whom appear to have no respect for the scientific method, and who think that every now and then they have to "solve Stonehenge".  The obsession with the narrative is everywhere, and the more spectacular and fantastical it is, the better.  They are all at it -- MPP, TD and the rest of them -- measuring their reputations not by the reliability of their research but by the ratings obtained by their TV programmes and the impact made by their ideas in the media.  The more column inches the better, since that measurement clearly has an impact on research grant allocations.  Garbage in, garbage out.  And as I keep on saying, they are the ones who write the nonsensical press releases.

Monday, 3 July 2017

Pitts reflects on Stonehenge


 Salisbury Plain -- plenty of digging still to be done.......


Mike Pitts has published a long reflection on Stonehenge, on his blog called "Digging Deeper".  It has a strange title, and looks as if it is about Donald Trump, but it contains much of interest. You can find it here:

 https://mikepitts.wordpress.com/2017/06/28/what-would-trump-do-with-stonehenge/

A lot of it is about the road / tunnel controversy (which I shall stay well clear of), and about the management of the site over the years, but there is a useful summary of the latest thinking on the early chronology, which is worth reproducing (with thanks).  Here it is:

The origins of Stonehenge are, appropriately enough you might think, a bit of a mystery. The puzzle is not one you will read about in guidebooks, or even much in academic research. It is a story that tells us much about how archaeologists think about Stonehenge.

You will hear often that the first structures, the beginning of the monument, are 56 pits (the Aubrey Holes) in a ring surrounded by a ditch whose chalk spoil is piled in banks on either side; the whole ensemble is about 100m across. The particular arrangement is unique, but what especially distinguishes it is what was buried in it: cremated human remains representing more people than found at any other such cemetery in prehistoric Britain. We don’t know exactly how many people (excavations early last century were not always well recorded, and part of the area has yet to be examined), but current estimates range from 150 to 240; there could be more. Like a Christian cathedral, right from the start death and burial were an important part of the meaning of Stonehenge.

So far so good. The way funerary remains were buried, scattered around the area almost furtively in small bags or boxes, seems to suggest that the ditch and the pits were not just repositories for the dead. If the ditch marked the edge of a sacred space, what of the Aubrey Holes? For long it was said they were just empty hollows dug in some lost ritual. Then 20 years ago, archaeologists decided they had supported large oak posts, and more recently it has been suggested they held not posts, but megaliths – bluestones, the site’s smaller stones from Wales. You can find archaeologists to back any of those theories; only new excavation is likely to offer a resolution.

The real puzzle comes when we ask, when did this happen? We cannot directly age an entirely prehistoric event, only certain things susceptible to scientific analysis. The best known technique is radiocarbon dating. With this we can estimate the age of bones left in the ditch, and then infer when it was dug. For obvious reasons, the best samples come from tools used in the quarrying, picks made from deer antler. These date the ditch to some time between 3000 and 2900BC – the figure we all quote for the start of Stonehenge.

But there is a complication. As well as the picks, the ditch contained a lot of old bones, some of them a century or more older than the tools apparently used to dig it out. Among them are a skull and two jaws from large cattle, buried by entrances into the circular enclosure; half a millennium before, in a different age when long burial mounds were being raised over uncremated bodies, we sometimes find such large cattle bones where we might have expected to see human remains. In three other cases Stonehenge bones dated to a century before the ditch are from cremation burials.

So we appear to have signs that Stonehenge was a place for the dead – shown by human cremations and great symbolic cattle heads – generations before Stonehenge existed. This is not a Stonehenge you will read about, because it’s not one archaeologists much talk about. It’s a ghost of which we know only of its apparent existence, and its association with the dead. Invisible for us, perhaps: but I’ll warrant it mattered at the time.

A lot happened in the eight centuries or more after the ditch was dug, architecturally at least, mostly involving big stones – look at the ruin today and imagine that restored in various permutations, and you’ll have a pretty good idea of it (naturally, there are many details that archaeologists do not understand). I tell the origin story, however, because of how it helps us picture the way we see the past. Almost everything that happened on Salisbury Plain thousands of years ago is unknown to us, like the ghost henge with no form. But we make a great mistake if we let our ignorance define what the past must have been like.

In 1805 William Cunnington, excavating furiously for his sponsor Sir Richard Colt Hoare, understood that the past was everywhere. Every mound he dug into, in every ditch and every backyard, he expected to find something – and usually did. That sense of an unlimited history, with a never-ending supply of new discoveries and information, was lost in the last century. Archaeology self-consciously shaped itself from a Romantic pursuit into a science. It dealt with evidence, not imagination.

Occam’s razor cut deep: relentlessly pursuing the simplest hypotheses about the past led to a gross over-simplification of what ancient societies were like, or were capable of achieving. It assumed that what you saw was all there was. At Stonehenge you gazed on a magnificent, sophisticated construction, but all around was a modern prairie: the stones seemed to spring from nowhere. Some archaeologists devoted themselves to excavating what they could of below-ground prehistoric remains, mostly burials, as ploughs and rotavators sliced into them. Others told the authorities there was nothing there to save. The losses were dreadful.

We have moved on, and thanks to the National Trust (and European Union grants) great swathes of downland have been returned to pasture, and what’s left of their archaeology survives. But the idea that what we see is what there was, has been harder to change. Every new discovery – and there have been many – is still greeted with astonishment. In the hands of the media every find rewrites history.

-----------------------------

I think I might part company with Mike on how the scientific investigation of the site (which he refers to as Occam's razor) has led to "gross over-simplification"  -- the trouble with Stonehenge studies is that there has always been too much speculation and too much story telling.  That still goes on, and in my view there is far too little proper science being done on Salisbury Plain, not too much.  

 And who has assumed that what you see on Salisbury Plain is all there is?  Surely the history of research at a wide variety of locations shows that archaeologists in general are perfectly aware of the abundant secrets still hidden beneath the turf?

But I agree (to some extent) with this: 
Every new discovery – and there have been many – is still greeted with astonishment. In the hands of the media every find rewrites history.
Mike places the blame on the media.  I place the blame on the archaeologists themselves, who are so obsessed with "ratings" these days that they keep on making outrageous claims about the significance of their work.  They, after all, are the ones who write the press releases.

Saturday, 1 July 2017

Literature Wales dumps Megalithomania video

 More news on the media portrayal of Rhosyfelin.

The breathless and reverential -- and really appalling -- video made at Rhosyfelin by Hugh Newman has been dumped by Literature Wales.  It had been embedded on the controversial Rhosyfelin page on the "Land of Legends" web site, and when I complained to Bronwen Price (who was responsible for the content of the site) she refused to move it.  Anyway, it has quietly been removed, so in this case common sense has prevailed......

https://brian-mountainman.blogspot.se/2017/04/more-rhosyfelin-gobbledeygook.html

The content of the web page is otherwise unchanged, since Dr Price considers it to be accurate.  Alternative truth prevails, in the somewhat complacent world of Literature Wales, which has declared itself to be "the national agency for literary tourism in Wales".

It appears that I am not the only one worried about Lit Wales and its delusions of grandeur.  In the recent Medwin Hughes Review of Welsh Government support for literature and publishing in Wales, Lit Wales is given a real going-over, and it's accused of  complacency, poor governance, elitism, and a rather dodgy habit of spending 75% of its income on its own staff salaries.  There is an extraordinary complaint about the fact that the Chair of Literature Wales, Prof Damian Walford Davies, apparently refused to meet the members of the Committee.

So it looks as if virtually all of its functions will now be handed to the Welsh Books Council.  Funding will be almost entirely withdrawn, and it is difficult to see how, in these circumstances, it can survive. A little bit of humility, and a willingness to accept advice from others, might have helped in the public perception stakes.......

The PDF of the full report can be accessed here:
http://gov.wales/topics/culture-tourism-sport/media-publishing/publishing/support-for-literature-review/?lang=en

Welsh Books Council recommended to take on Literature Wales' Book of the Year 

(Article in The Bookseller)
http://www.thebookseller.com/news/welsh-books-council-take-literature-wales-book-year-569671

Literature Wales to have funding cut after damning report
(BBC report)
http://www.bbc.com/news/uk-wales-politics-40282717

Wednesday, 28 June 2017

More on quarrying

....... by which I mean glacial quarrying, the process by which chunks of bedrock are removed and entrained within overriding ice.

As a reminder, here is Prof Dave Evans's definition:

Quarrying (Prof David Evans)
Progress in Phys Geog 2004
 

Quarrying
Quarrying involves two separate processes: (1) the fracturing or crushing of bedrock
beneath the glacier;  and (2) the entrainment of this fractured or crushed rock.  Fracturing
of bedrock may take place where a glacier flowing over bedrock creates pressure
differences in the underlying rock, causing stress fields that may be sufficient to induce
rock fracture (Morland and Boulton, 1975; Morland and Morris, 1977). Fluctuations in
basal water pressure may also help to propagate bedrock fractures beneath a glacier
(Röthlisberger and Iken, 1981; Walder and Hallet, 1985; Iverson,1991a). Brepson(1979)
has successfully simulated the sliding of temperate ice over an obstacle in the
laboratory, and noted that large cavities form in the lee of obstacles, aiding quarrying.
Evacuation of rock fragments along joints in the bed is possible where localized basal
freezing occurs, for example as the result of the heat-pump effect proposed by Robin
(1976). Although Holmes (1944) originally argued that quarrying could occur beneath
both thick and thin ice, and outlined a theory based on pressure-controlled freezing of
meltwater in joints in bedrock, there is now general agreement that quarrying is
favoured beneath thin, fast-flowing ice (Hallet, 1996). Modelling studies indicate that
low effective basal pressures (0.1–1MPa) and high sliding velocities are the dominant
glaciological conditions required for quarrying because these conditions favour
extensive ice/bed separation (subglacial cavity formation)and also concentrate stresses
at points, such as the corners of bedrock ledges, where ice is in contact with the bed
(Iverson, 1991a; Hallet, 1996).


According to this theory, it may be that many of the features I have recently (again!) been looking at in the Stockholm Archipelago are very recent indeed -- formed just before deglaciation, which occurred here around 11,100 years ago.  Dave is picking up on a suggestion from many writers that when ice is very thick, movement on the bed might be negligible, with conditions effectively protecting rather than eroding the landscape beneath.  So for each glacial episode there might be two "erosional episodes" -- one at the outset of the glaciation, and the other at the end.  On the other hand there are other observations that suggest that thin ice may have a polar thermal regime on the bed, which means freezing-on and bedrock protection -- with erosion increased when the ice thickens because there may be a temperate thermal regime on the bed -- meaning high sliding velocities and considerable meltwater lubrication.  The truth is always more complicated than one would like it to be.........

Anyway, one thing that is blindingly obvious in the archipelago is that on the stoss (upglacier side) of all bedrock knolls and other roche moutonnees, abrasion and polishing features predominate, whereas on the lee side of all features plucking leaves rough and even jagged surfaces which show us where bedrock chunks have been dragged away.

Here are some photos of stoss-side slopes on RÖDLÖGA STORSKÄR:






Now here are some from the lee-sides or down-glacier sides of the same bedrock hillocks -- note how jagged surfaces, sharp edges and broken rock predominate.






 The only rounded or sub-rounded lumps of rock in environments like these are the glacial erratics dumped more or less at random during ice wastage.   It would be good to show some of these sites to certain British archaeologists, who would presumably (unless instructed otherwise) assume that all of them are Neolithic quarries littered with monoliths that were left behind by the builders of Stonehenge......





Monday, 26 June 2017

Roches moutonnees in the Stockholm Archipelago

 Two images of moulded and streamlined topography on Pre-Cambrian Basement rocks in the Stockholm Archipelago. Location -- west side of Rödlöga Storskär.  In both photos the ice has moved from right to left.  Note the streamlined ridges and gullies.  In the lower photo we see the stoss side of a large roche moutonnee -- apart from a few plucked faces on miniature roches moutonnees, all the surfaces are smoothed and rounded off by powerful abrasion.  The ice here has been under compression, probably melting on its bed.


I have done many posts on this topic before -- and will probably do more in the future, if fate decrees that I have more visits to the extraordinary and beautiful islands of the outer archipelago.  I have just spent three days out there. and these notes and pictures are the result.

Wherever you look on the washed rock surfaces there are asymmetrical forms.  We would call many of them roches moutonnees, and they occur on many different scales.  Some of them are substantial hill masses, over 20 m high, and others are measurable in centimetres.  They should not be confused with whaleback forms or rock drumlins, which tend to have abrasion / polishing features on all flanks;  in contrast,  roches moutonnees always have gentle up-glacier (stoss side)  slopes that are polished and steep down-glacier (lee side) slopes that are fractured and steep.  Different processes are at play -- and the key to the form is the ability of ice to exert immense pressure and to "quarry" vast chunks of bedrock which are then entrained and carried away.  This is how erratic slabs, boulders and pillars are formed........

In the archipelago the ice moved consistently from north to south, with minor variations dictated by local topography.  There was erosion on a considerable scale during the Devensian glaciation, with the ice of the Scandinavian ice sheet again grinding down old surfaces affected by ice many times before. Parts of the eroded surface are covered by till and fluvioglacial materials, but because the surface was covered by water after being covered by ice, it has been well washed, with fines carried away into deeper water -- leaving behind a classic erosional landscape that can be examined in minute detail.

Herewith some more photos:

 A mini-roche moutonnee, just a few cm high.  The watch shows the direction of ice movement.  Smoothed and abraded face on the right, and plucked (fractured) face on the left, shown up by the lighter colour on the rock.

 This roche moutonnee is a bit bigger.  Here the direction of ice movement is again obvious.  The stoss side is heavily striated, and the fractures on the lee side are quite complex. There have probably been several phases of block removal.
 
 Another small roche moutonnee.  Here it looks as if there has been just one phase of block removal -- the fractured face is much simpler.

 There is a more complex fracture pattern on this lee side, and the shape of the roche moutonnee is quite irregular.  Note the big crescentic gouge on the abraded surface in the background

Sunday, 25 June 2017

Striations in the Stockholm Archipelago

Not all rock surfaces are susceptible to the process of scratching or striation.  In this part of the archipelago this grey fine-grained gneiss (?) reveals crossing fractures and a smoothed striated surface.  The pink granite (?) in the background contains large masses of quartz crystals, and reveals no striations at all, breaking up into a broken and rough surface.  In the foreground is a scar left by the removal of a large bedrock block on the down-glacier or lee side of this slight ridge.

Another heavily striated surface on fine-grained gneiss.  The crossing fractures are lines of weakness which are exploited by the quarrying process by which one block after anther is dragged away by the overriding ice.

 Heavily smoothed and striated bedrock, with a marked fracture scar in the bottom left quadrant of the photo.  This scar shows no traces at all of ice action, suggesting that it is very fresh.

Striations in  the Stockholm Archipelago.  Here, in an area of Pre-Cambrian basement rock with relatively low relief, there are abundant traces of glacial erosion on rock surfaces just above present sea level. The ice of the Scandinavian ice sheet retreated from this area around 11,200 years ago, at a time when the land surface was greatly depressed.  The retreating ice edge was probably floating, and the whole landscape was then deeply inundated by the sea —  to emerge bit by bit as isostatic recovery ran its course.  Isostatic recovery is still going on today, at a rate of c 1 cm per year. 

The last erosive ice to affect this landscape was flowing almost exactly north— south, and this is the direction followed by most striations.  However, there are deviations of as much as 30 degrees, since the ice adapted its flow patterns to the details of bedrock morphology.  We can even say that it adapted to micromorphology, with measurable deviations across an area of a few square metres where there are ridges, gullies and knolls.

How old are the striations?  There are occasional crossing striations, but not many.  I suspect that they are quite fresh, dating from the Weichselian / Devensian glacial episode.  I also suspect that during that glaciation, over a timespan of maybe 20,000 years, there were not many deviations in ice movement direction.  The ice always flowed from the north towards the south.  Given the micro-adaptations we can see on the striated rock surfaces, the ice was remarkably fluid, suggesting considerable meltwater lubrication — but this was not a “wasting ice” situation, since the effects of gouging, rock fracturing and block removal are in many cases quite spectacular, suggestive of situations in which the ice was “frozen on” to the bedrock surface. Striations are in themselves indicators of hard basal ice capable of pressing rocks and rock fragments into the bedrock surface over which it was flowing. I suspect rapid alternations between freezing and basal thawing and sliding — a classic situation for optimal glacial erosion and areal scouring. 

Most of the striations in the photos are less than 5 mm deep, but some are up to 2 cm deep.

Tuesday, 20 June 2017

West Greenland tsunami


From the BBC web site -- one of the houses swept away by the wave

Some images are appearing from West Greenland following the tsunami that struck the coast yesterday.  It looks as if one small village bore the brunt of the wave -- around 30 homes were destroyed, and four people are missing.  Damage in other communities was on a smaller scale.

Tsunamis are extremely rare in Greenland, although plenty of dangerous waves are produced in front of calving glaciers and when large bergs roll over.  This one is thought to have been triggered by an underwater earthquake -- and the water displacement (a prerequisite of all tsunamis) may have happened as a result of an underwater landslide or from a large landslide on a steep fjord side.  In the latter case, there will be an obvious landslide scar.  More info will no doubt be forthcoming -- but this is a very remote area.