THE BOOK
Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Wednesday, 29 February 2012

Paviland and the ice edge

 Goat's Hole Cave, Paviland, on the Gower Peninsula.  Below: an artist's reconstruction of the laying out of the young man whose bones are now dated to c 26,000 years BP

I have done a few posts in the past about Paviland and the Red Lady -- use the search facility to find them.  In some recent posts I have been speculating about what might have happened in the Carmarthen bay and Cardigan Bay areas during the Early and Middle Devensian -- and Paviland is one of the few places where evidence from archaeology and geomorphology might come together to give us some answers.

A good summary of the state of knowledge about Paviland is found here:

http://www.britarch.ac.uk/ba/ba61/feat3.shtml

and there was a somewhat imaginative reconstruction or dramatisation of the interment of the young man (mistakenly referred to for many years as "The Red Lady") in the opening sequence of "The Story of Wales" on BBC1 the other evening.  (You can see this sequence on the BBC  iPlayer.)

http://www.bbc.co.uk/programmes/p00pj67h

http://www.bbc.co.uk/programmes/p00pd0jp

To quote from Stephen Aldhouse-Green:

At the time when the young man was ritually interred, there is no substantive evidence in this remote part of Europe for a human presence that was other than episodic. Indeed, faunal compositions and densities probably oscillated over time and space. Human presence in the British early Upper Palaeolithic may plausibly be linked to a 'biomass expansion', an overall increase in the availability of animals and other forms of food, centred on the 29th millennium. The coincidence of the dating of burnt bones to this period, combined with the presence of burnt Aurignacian artefacts, supports this as the most likely time for Aurignacian presence at Paviland. Radiocarbon dating of an Aurignacian bone spearpoint to around 28,000 bp at nearby Uphill lends additional weight to this interpretation.
Gravettian visitation is attested by a scatter of large tanged points occurring across southern Britain, including Paviland. Such points are generally dated to 28-27,000 BP, although their use may possibly extend down to the time of the 'Red Lady' burial..........

............ Restudy of the Goat's Hole lithic collections has confirmed material ranging from about 40,000 BP to about 13,000 BP (including Mousterian, leaf point, late Aurignacian, early Gravettian, Creswellian, and Final Upper Palaeolithic phases), although the earliest and latest phases are not dated by radiocarbon. Aurignacian finds form the dominant element. These artefacts were made from a range of imported and local raw materials.

So the signs are that there was possibly continuous -- or more likely intermittent -- occupation of this Carmarthen Bay coastal area right through from the Early Devensian to the Late Devensian.  The most favourable conditions for occupation might well have occurred during the episode known as the Upton Warren Interstadial.   Did the occupants of Goat's Hole and the other limestone caves around this coastal lowland (including the Caldey Island caves) also live here and die here at the peak of the Devensian glaciation, around 23,000 years ago?  With Devensian glaciers coming down from the Welsh valleys and creating end moraines not far from the position of the present coastline, did the hunters of the time occasionally stray onto the ice, or hunt along the ice edge?  Or was there such a hostile environment at the time that they retreated southwards, and returned once the glaciers had started to melt away?  And what is the relationship of Paviland Cave to the Paviland Moraine  (supposedly of Anglian age)  of Prof David Bowen?

Could Devensian ice have actually flowed across the mouth of the cave and sealed it off for a while?  The current consensus is that this did not happen, and that the ice edge lay maybe a couple of miles to the north, across the middle of the Gower Peninsula;  but I am not all that convinced by the evidence for that, and as I have said earlier, I think that Devensian ice might well have overridden Caldey Island and substantial parts of the territory now submerged beneath the waters of Carmarthen Bay.

Lots more questions.....



Tuesday, 28 February 2012

The bluestone argonauts -- why would they bother?

 A still from the BBC programme "The Story of Wales"

Last night we saw the first episode (number 1 of 6) of the BBC Wales / OU blockbuster series called "The Story of Wales" -- which dealt with prehistory.  In the section dealing with the Neolithic / Bronze Age some time was given to Prof John Koch, who made the point that the old idea of eastern tribal supremacy and conquest spreading westwards from the east and into the Celtic Fringe or Atlantic Seaboard was now discredited to be replaced by a view of the world in which the land was the least favoured option for moving about, with the early tribes (the Celts and their precursors) spreading gradually along the western coasts.  Then tribal trading contacts were maintained by sea rather than overland.  The view is now (according to Prof Koch) that trade, rather than invasion and conquest, was the driving force in the creation of what would later be "the Celtic World" of western Britain.

I have always thought that the idea of the human transport of the bluestones from West Wales to Stonehenge is underpinned by a presupposition that there was a dominant society in Wessex and a subservient tribal society in West Wales.  In other words, the Wessex tribes were more advanced and more powerful, leading to a situation in which they could collect stones from the far west with impunity, or on a whim, and that they had the manpower and technical expertise to do it -- or else that the western tribes might wish to carry the stones to their eastern neighbours as a form of tribute or homage. 

Might this version of events now need to be fundamentally revised?  If the Wessex tribes were not necessarily any more advanced or powerful than those of Pembrokeshire, and if the people of the latter area were perfectly happy, thank you very much, why would they bother to cart lots of very heavy stones all the way to Stonehenge?

It all gets very convoluted, and indeed MPP and his colleagues have explored this issue before, at the famous lecture in Newport last summer.  There, they argued for two very powerful tribal groups who came together in a great social and economic alliance -- in the first great political "unification."  The moving of the stones was the great symbolic act that cemented the union.   All highly fanciful -- see my posts here:

http://brian-mountainman.blogspot.com/2011/09/are-you-sitting-comfortably.html


http://brian-mountainman.blogspot.com/2011/10/stuff-of-nightmares.html

http://brian-mountainman.blogspot.com/2011/09/hq-of-nevern-valley-tribe.html

My problem with at least some of this is that I don't know how widely accepted this "revisionist" view of prehistory actually is.  As Wales and Scotland assert their identities and grab political control back from England, bit by bit, there is of course a tendency (encouraged by Welsh universities and research institutions) to flag up the "uniqueness" of the prehistoric heritage -- in exactly the same way as HHT used the bluestone transport debate to bolster English self-esteem after the First World War.    Sadly, we are never all that far away from political motives, even in what seems to be a rather esoteric debate about cultural assimilation, dispersal, parallel development and so forth........


Monday, 27 February 2012

Bluestones and sarsens



Phil Morgan has kindly sent me this excellent photo of some of the bluestones and sarsens at Stonehenge, and is happy for it to be published.  Thanks Phil.....  Click to enlarge.

One thing that strikes me yet again is that there is really no difference in colour between the bluestones and the grey stones!  But of course, when some (but not all) of the bluestones are broken or seen with fresh unweathered surfaces they do appear to be a bluish grey colour.

Phil's notes:

From Left to Right

Sarsen Circle Trilithons = 28, 29, 130, 30, 101, 1, 102, 2, 3, (5 + Bluestone 33);
Bluestone Circle = 46, 47, (48 fallen), 49, 31, (150 and 32 fallen), 61, (61a stump), 62, and 63.
Left foreground = Broken Sarsen Lintel 160b and 160c.

Incidentally, the stones of the Bluestone Circle, 46, 47, 49 and 31, listed above are the four orthostats referred to in paragraph 3 of Rob and Richard's paper on Craig Rhos-Y-Felin, 2011.

Lots of Earth Science -- why?

 The Gibbard - Ckark reconstruction of the limits of three different glaciations in Southern Britain.  These limits are crude and in some instances nonsensical in that they fail to take account of evidence on the ground or of glaciological principles.  Somehow or other, they have to be improved upon......

My faithful readers will have noticed that there has been a lot of earth science material posted on this blog in recent days -- and you might wonder what it is all doing on a site called "Stonehenge Thoughts."  Well, it's all part of my ongoing attempt to understand how glacier ice behaves in the SW quadrant of the British Isles -- and the nature of the "controls" that influence the course of events during the glacial episodes that we know about.  When, and how, did glacier ice extend into Somerset and possibly Wiltshire, during the Anglian or any other glacial episode?  We won't understand this until we know what the interactions are between Welsh ice and Irish Sea Ice -- and because the Anglian glaciation occurred around 450,000 years ago we don't have a lot of evidence to go on.  But if we can get a reasonable idea of what happened during the Devensian, we can use that as a good analogy or guide to understanding.

What I'm trying to do here is test the glacial hypothesis to destruction.  This is, sadly, not something that the archaeologists have done with the human transport hypothesis.......

Saturday, 25 February 2012

Glacial deposits from the Early Devensian?

On looking through the records to see what there might be in the way of field evidence for an expanded Welsh Ice cap in the Early Devensian, the records are not easy to interpret.  Following the Ipswichian interglacial (O18 stage 5e) -- around 120,000 years ago, there was a long period of cool - cold - periglacial - glacial conditions, with lots of climatic oscillations, between 116,000 BP and 59,000 BP.  Some of these oscillations are given the O18 labels 5a - 5d, and then around 70,000 years ago came the sharply oscillating climate labelled as O18 stage 4.  That stage lasted for maybe 12,000 years -- see the earlier posts.

The coastal drift stratigraphy around Wales fits into this framework rather well -- with thick slope deposits (with much evidence of periglacial conditions and permafrost or frozen ground conditions now and then) sitting on top of the Ipswichian raised beach and beneath the glacial deposits assumed to date from the LGM of the late Devensian.  (See the stratigraphic columns for Pembrokeshire coastal sites in the earlier post.  Similar relationships are seen elsewhere in Wales.)

But then we have some rather mysterious exposures of tills that seem to pre-date the LGM -- at Criccieth,  Glanllybnnau,  Llanystumdwy,  Moranedd, and New Quay.  Do these tills date from an early expansion of ice from the Welsh Ice Cap which acted as a sort of precursor to the arrival of the Irish Sea Glacier?  (Big glaciers always take longer to react to climate change and then to build towards their maximum extent than smaller glaciers do.)  Or was there genuinely an interval between these two glacial "events" which coincided with the Middle Devensian interstadial episode conventionally labelled as O18 stage 3?



The "weathering layer" (assumed to have been formed during a warmer interlude)  seen above the Criccieth Till in the cliffs at Glanllynnau is overlain by fluvioglacial sands and gravels, with another till (called the Llanystumdwy Till) above that.  The weathered layer is a yellow-brown horizon on top of a blue-grey clay-rich till -- but we need much more evidence than a simple colour change before we can be sure that the top surface of the till has genuinely been affected by surface weathering under a warmer climate.  The upper surface of the Irish Sea till in Pembrokeshire is often decalcified and weathered in this way, simply because ground-water passes through overlying fluvioglacial deposits quite easily and then penetrates into the till beneath.  The colour change has nothing to do with surface exposure and nothing to do with a warmer climatic interlude -- it is simply a matter of chemistry.......

But on the other hand, in North Wales coastal sections  there are signs of solifluction features and also ice-wedge casts associated with this weathered horizon, and that has to mean there was an interval of non-glacial conditions before ice returned to deposit the upper layers in the sequence. 

This debate has some way to run.....


Friday, 24 February 2012

Arthur's Stone, Gower


On looking into the Paviland Moraine, I came across a number of references to Arthur's Stone, on the Gower -- a very large erratic of Namurian gritstone (I think) apparently derived from the North Crop of the Coalfield.  According to Prof David Bowen there are many other erratics from this source in the area of the Paviland Moraine, indicating that the ice that carried them came down from the north towards the South Wales coast.  It seems that this was one of the largest capstones in Wales, which at some stage has broken into two or more pieces......

Does anybody know anything more about this feature?  It looks like a rather crude Neolithic burial chamber.  Apparently there are a number of other burial mounds and later features (Bronze Age?) in the area.

Update:  According to the GCR for the Quaternary of Wales,  there are abundant Namurian "quartzite" erratics in and beyond the Paviland Moraine -- the key source is assumed to be Mynydd-y-garreg in Carmarthenshire.  Some boulders of this same rock type are found on the foreshore at Western Slade. 

The Early Devensian Welsh Ice Cap


I have been having a little discussion with Henry Patton about the likelihood of an Early Devensian Welsh Ice Cap growing sufficiently to extend beyond the present coastline.  Henry kindly sent me the above graph, which represents one of his early attempts to model the volume and extent of Welsh ice, plotted against the GISP2 oxygen isotope data for Greenland.

On the graph, the Last Glacial Maximum (LGM) shows up very clearly, with a very rapid ice expansion after a long period (10,000 years or so) of small-scale glacier expansion and contraction in the uplands.  the remarkable speed of ice cap expansion and then collapse is very impressive -- shown on this graph as falling in a period of around 5,000 years and centred on 24,000 yrs BP.  One might reasonably conclude that a long period of cold and snowy conditions is a prerequisite for ice expansion on a substantial scale.......  but the oxygen isotope data do not adequately explain the sudden increase in ice volumes and the sudden expansion of the glaciated area.  Other very important factors must have come into play......

As for the Early Devensian, we can assume that there was a Welsh Ice Cap in existence between 60,000 and 70,000 years BP, and maybe for  a few millennia before and after -- but it does not seem to have been more extensive than about 400 sq km (as compared with 30,000 sq km in the LGM).  What is interesting from the O18 graph is the huge climatic oscillations that seem to have occurred at this time, with temperatures apparently plummeting to a lower level than at any time during the LGM -- balanced by very rapid warming phases.  Maybe this sort of climatic instability was just not right for the gradual buildup of ice over the Welsh uplands..... 

Around 50,000 years ago there does seem to be evidence of a warmer period -- albeit with cold snaps now and then -- and this seems to me to accord with the evidence for the weathering of Early Devensian periglacial slope deposits around the coast.  Many other authors in other parts of the UK have brought forward evidence for one or more "Middle Devensian Interstadials."

To return to the Early Devensian Welsh Ice Cap, and the apparent mis-match between my field evidence from New Quay and the glacier modelling done by Henry, we still have to find out whether there are deficiencies in the model or misinterpretations of the field evidence.  Probably a bit of both......

Then we have the interesting question of the "Paviland Moraine" in western Gower, assumed by Prof David Bowen to be of Anglian age.  I'm not all that convinced by the dating of that feature -- could it be of Early (or even Late) Devensian age?  Watch this space.....

North Pembrokeshire Glacial Striations


The other day I forgot to give the hard data on the glacial striae plotted in 1962-1965 in North Pembrokeshire.  During my fieldwork I plotted hundreds of striae, mostly on smoothed rock slabs close to the coastline.  The magnetic variation at the time was 7 deg and 20 minutes west of grid north.  The compass directions below are as I recorded them -- on the map above they are corrected.  Within the circles I have only put selected striae directions -- deemed to be the most common.

Note that ice movement directions can be heavily influenced by the nature of the bedrock and the orientation of the coastline and the cliffs -- so a "regional" ice direction movement may be locally disrupted, with ice moulding itself to the topographic features of the coastline.  There may be highly localised swings of maybe 30 degrees to either side of the regional ice flow direction.  But the overall ice movement directions do come through if you measure enough striations......

 Striated bedrock slabs, Whitesands North


Here are the records:

1.  Ogof Golchfa:  90 -140, mostly 125, 80, 33, 25
2.  Whitesands South:  115 -190, mostly 135
2.  Whitesands North:  100 -160, mostly 133, older striae 180 - 230, mostly 223
3.  Porthmelgan:  120 - 160, 140 - 190, 230, mostly 160
4.  Pen Deudraeth (Aber Mawr)  122, 148 (older?), 173 (newer)
5.  Parrog (Newport)  113 - 173, mostly 160
6.  Newport Sands:  160
7.  Gwbert (Cardigan):  115 - 155, 163, 183, mostly 135

Thursday, 23 February 2012

Mystery erratics on Newport beach

Now then -- a little puzzle.  These are samples from the erratic boulder found on the beach in Newport estuary a couple of weeks ago.  Each of the fragments is about 8 cm long.  The boulder is sitting on the beach between the tide marks, in the middle of quite an extensive area of till which was previously covered by estuarine mud.  A few yards away from the boulder, on the surface of the till, I found a small coin last Sunday -- which turns out to be a George III halfpenny -- the date seems to be 1798.  Does that date the glaciation that deposited the till?  I doubt that -- so let's move swiftly on......

I don't recall seeing a boulder of this type before -- it is certainly not local.  To me, it looks like a felsite -- partly because of the texture, but also because of the characteristic "dendritic" or fern-like patterning on the weathered surface.  The early geologists (including HH Thomas!) found felsites in the Newport area which they interpreted as "Cader Idris or Arans felsite."   Whether these fragments can be given the same provenance remains to be seen.

Opinions, Rob or Richard or anybody else who knows igneous rocks?

If this really is a felsite boulder from the Cader Idris area, that would be quite interesting, because the movement of such a boulder must have been in at least two stages -- first, movement broadly westwards out from the Welsh uplands by a Welsh ice stream, and second, movement southwards by Irish Sea ice which crossed Cardigan Bay and impinged on the North Pembrokeshire coast.

That, as you keen observers will have noticed, is precisely the mechanism I have proposed for the transport of the Altar Stone towards Stonehenge......... except that we need broadly southwards movement by Welsh Ice and broadly eastwards movement by the Irish Sea Glacier.  From what we know about ice movement directions, that is perfectly feasible.

More on the Early Devensian

Oxygen isotope records for the Devensian -- assumed to be a reasonable representation of temperature oscillations and of glacial and non-glacial conditions in the mid-latitudes.  Note that in the bottom graph the time scale runs in the opposite direction!

Further to my last post, we now have a multitude of environmental reconstructions to work off, many of them based on oxygen isotope records from Greenland and Antarctica, and others from deep sea cores etc.  It seems that there was a very distinct cooling around 60,000 - 70,000 years ago -- a period conventionally labelled "Oxygen isotope stage 4."

The key question is this:  was that cooling episode prolonged enough, and was it characterized by sufficient precipitation in the form of snow, to trigger off a true glacial episode in the UK uplands?  

In an interesting paper called "The Last Glacial Stage (the Devensian) in Northwest England" (NW Geog, 2003, vol 3 (1)) Catherine Delaney suggests that in OI Stage 4 there was a sharp temperature reduction, a drop in sea level to -60m and a number of short-term cooling events.  She suggests that the British - Irish ice sheet was in existence at this time and that there was an ice stream in the Irish Sea basin.  Some authorities think that the ice was restricted to northern Britain, but Prof David Bowen and others have argued for an ice cover in Ireland at the time as well.  There were valley glaciers in the Lake District at this time, as indicated by lake sediments.  In these circumstances it is inconceivable that there was NOT a Welsh ice cap at this time.  But was it big enough to expand beyond the present coastline?

Henry Patton's work suggests that for the development of a sizeable Welsh ice cap you need quite a prolonged period of low temperatures -- ie a degree of climatic stability.  How long does this stable cold period need to be?  Around 15,000 years?    Watch this space.....

Wednesday, 22 February 2012

An Early Devensian Glaciation in Wales?

 
Did a glacial episode like this also occur around 60,000 - 70,000 years ago?

In my ponderings on how the Welsh ice cap and the Irish Sea Ice Sheet might have expanded, contracted and interacted in the Anglian Glaciation,  I decided to take a look again at Henry Patton's ice cap models, which are here:

http://henrypatton.org/academic-research/ice-sheet-models

I was struck by the second model on the site, in which Henry reduced temperatures by 2 degrees C  in order to see what happened.  Lo and behold, a single phase ice expansion was replaced by a double phase glaciation, with extensive ice cover occurring around 29,000 yrs BP and around 23,000 yrs BP. (Correction 23.2.2012;  Henry points out that I have misunderstood this.  Apologies -- if I had examined his graph properly I would have seen that the 2 degree reduction was applied to both models, but that on the second model he applied a further temperature reduction of 0.2 deg over an extended period prior to the glacial maximum.)

Now that's rather interesting because I have always thought that in West Wales the Early Devensian was a time of intense cold -- with prolonged periglacial activity and with long periods when the ground was affected by permafrost.  That is shown in all of the coastal stratigraphy which I examined back in the good old days when I was a research student.  Stratigraphy doesn't lie.    The classic site is Abermawr (see below), where there is a variable periglacial deposit (4) with a weathered upper surface, underlying the Irish Sea till (5).  So if the Irish Sea till was deposited during the ice advance that occurred in the Late Devensian, it seemed entirely reasonable to me (and it still does) that the periglacial materials accumulated during the Early Devensian and that they were subjected to weathering during a slightly warmer Middle Devensian "warm episode."  See also:

http://brian-mountainman.blogspot.com/2011/01/strata-do-not-lie.html


 That interpretation of events was not at all widely accepted in 1965, but it accords very well indeed with what we now know of the Late Pleistocene climatic oscillations.  According to the chart below, the cold episode of the Early Devensian lasted for more than 50,000 years, starting with O18 stage 5d and ending with O18 stage 4.

So if it was cold (and sometimes VERY cold) during the Early Devensian in the Pembrokeshire Peninsula, it is entirely reasonable to assume that at various times there must have been a Welsh Ice Cap growling away in the distance, expanding and contracting as the climate cooled and warmed.

This is not just an academic point.  At New Quay there is a strange deposit beneath the Irish Sea till which I took in 1965 to be a soliflucted local till, laid down by an earlier advance of Welsh ice out from the mid-Wales uplands and extending westwards to a position beyond the present coastline.  I don't think this Welsh ice expansion reached Cardigan.

Along the Cardigan coast between New Quay and Aberystwyth there are many places where thick "head" deposits are sometimes more than 40m thick.  These have been interpreted as accumulated layers of solifluxion deposits showing that these coasts were not glaciated during the Devensian -- but that story can now be discounted, and recent research suggests that the "Blue Head" is a soliflucted or rearranged Welsh till, related to ice flowing down across the coast from a Welsh Ice Cap.  The favoured interpretation seems to be that the "rearrangement" of this material occurred after the peak of the Late Devensian glaciation.  I think the deposits are too thick for that explanation to be tenable -- and I suggest that the glacial deposits were emplaced in the Early Devensian (let's call this the New Quay glacial episode) and later rearranged by solifluxion processes under the coastal slope.  Later on still, during the Late Devensian, these materials were all frozen solid, and the ice from the Welsh Ice Cap passed over them once and maybe twice, without having any great effect on them.  (These are the episodes illustrated in Henry's models.)  Then there was some further rearrangement of the surface materials in the Late-glacial, giving rise to the "Brown head" which we see close to the surface today.

For me, that explanation accords most accurately with the evidence on the ground, and it will be interesting to see whether Henry's most recent modelling experiments support or contradict my proposed sequence of events..........

Here be bluestones

Here is a nice graphic from that news programme -- from the YouTube video which Pete put together.  Nothing new, but it shows the positions of the bluestones quite nicely........

The Millennium Stone pull -- a blast from the past



Grateful thanks to Pete G for producing this from the archives.  Ah -- I remember it well.....

I had forgotten that before the pull proper was done, there was a big trial on Withybush Aerodrome -- on the runways -- to check on the method (sledge plus lots of ropes and lots of Netlon) under the direction of Nick Price.  As he said, even under those pretty well perfect conditions, he was surprised just how many people were needed to get the stone moving........

Tuesday, 21 February 2012

Those Meltwater Channels

The Gwaun - Jordanston System of meltwater channels in North Pembrokeshire -- possibly the most impressive suite of subglacial channels to be found anywhere in the world.  Several of these channels are cited in SSSI citations, and since they are deemed to be "classic landforms" they are carefully protected within the Pembs Coast National Park.    The Gwaun Valley is the most spectacular -- that's the one which runs in a long loop from the right-hand (east) edge of the images and out at the coast at Fishguard -- effectively cutting off the Carningli-Dinas Mountain massif from the rest of the Preseli uplands.

The image above (courtesy Jonathan Lee) shows the channels wonderfully well -- click to enlarge and see more detail.

The orientation of these channels has always been problematical, because they suggest that at the time of formation ice was flowing across the landscape from NE towards SW.  That's not at all the direction of ice movement which we pick up from the erratic trains and striae in Pembrokeshire fieldwork.  But there are some striations in the St David's area (see previous post) that suggest ice movement from NE towards SW, even out at the tip of the peninsula.  That means unhindered Welsh ice flowing out into St George's Channel at some stage.  When might that have been?  Well, I think the channels are very old, since they contain lodgement till and fluvioglacial deposist probably dating from the Devensian.    My interpretation of the age of these channels is very different from that of Prof David Bowen and others, who have thought of them as Devensian features associated with ice wastage maybe after 23,000 years ago.  But there are major problems with that dating.  So my interpretation is that the channels were formed maybe in the Anglian Glaciation, at a time when Welsh Ice was dominant -- and when there was no Irish Sea Glacier occupying St George's Channel.  It's most reasonable to assume that this was in an "early Anglian"phase, after which the Irish Sea Glacier expanded and established an ice flow across the channel complex, with ice moving from NW towards SE.  So the channels would have been plugged with stagnant ice while more active ice sheared over the top of them.  Parts of the channels would have been used and refreshed (and altered) during deglaciation, and then again during later glacial phases including the Devensian.

That's my story for now, until somebody comes along and convinces me that the evidence supports another one!

Sunday, 19 February 2012

The Fluvioglacial Landscape near Monington

Thanks to Jonathan Lee and Aberystwyth university, here is another stunning image from North pembrokeshire, made by processing digital stereo aerial photography  -- as mentioned before, we can see altitudinal changes to an accuracy of 2m, with the 3D effect caused through the application of "false lighting and false colour." Low level lighting is thrown from the NE.

What we see here is the extraordinary fluvio-glacial landscape in the area around Monington, on a broad plateau surface midway between Newport and Cardigan.  These features have been known for many years, and have been mapped by many fieldworkers including Prof David Bowen and yours truly  -- but nothing before has shown up these features with this level of accuracy.  Notice that most of the landscape is smooth -- but from the centre of the image up to the top edge, and in some areas to the left, the land surface has "excrescences" or rough blotchy areas which look very different.  These are the fluvioglacial accumulations left behind at the end of the Devensian glaciation -- including eskers, kames, kame terraces and even kettle holes where detached ice masses have melted out.  It was the presence of these features that led Charlesworth in 1929 to define the "South Wales End Moraine" in this area -- thereby triggering off endless debate about ice limits and dating.

These features are not particularly "linear" -- so what are they doing here?  Our best guess at the moment is that the ice extended well to the south of this point, and then when melting started, the ice thinned until the hilltops in this area started to protrude -- setting off enhanced rates of melting, and the accumulation of fluvioglacial materials in the pits and hollows thus created.

Saturday, 18 February 2012

North Pembrokeshire Ice Flow Directions

Above:  a synthesis if known ice movement directions across Pembrokeshire (many lines of evidence; many sources).  No particular glaciation portrayed -- but most evidence comes from the Devensian.  Click on this map and the others to see them enlarged.


The classic map of glacial erratic trains in Pembrokeshire -- a synthesis from Griffiths (1940) based upon his own fieldwork and the work of the Geological Survey surveyors (Cantrill, Thomas, Strahan and Dixon in particular).
Key:  
4 Preseli rock types (dolerite, spotted dolerite, rhyolite etc)
5  Roch - Hayscastle erratics
6  St Davids granite
7  Ramsey Island volcanics
8 St David's Head gabbro
9  Clegyr agglomerate
10  Llandeloy porphyrite
11  Cader and Arans felsite
12 Green Harlech grit
13  New Inn pyroxenic keratophyre 
The line enclosing the Preseli Hills marks the approximate boundary between Irish Sea Drift (till) and Welsh Drift.  Outside the line there are many erratics which have come from Irish Sea sources -- inside the line (to the east) the erratics are much more difficult to provenance, comprising mostly shales, mudstones, sandstones etc from the Silurian sedimentary sequences of Mid-Wales.


 
 Glacial striae at coastal locations in Pembrokeshire.  This map has never been published before -- data from my field notes 1962-1964.  Compass deviation just over 7 deg W from grid N in 1964.  Corrected on this map.  Sites:  1 is Ogof Golchfa; 2 is Whitesands; 3 is Porthmelgan; 4 is Pen Deudraeth (Abermawr); 5 is Parrog; 6 is Newport Sands; 7 is Gwbert.  Most common directions are shown; in reality much more variation at each site.  This map confirms that for some of the time ice flow has been almost N-S -- but for most of the time the ice has come in from the NW quadrant.  There is one very intriguing feature -- some old striations indicating an ice flow from NE towards SW.  That means Welsh ice flowing down into St George's Channel, unhindered by Irish Sea ice.  I'll put up another post about this apparent anomaly.

 
JC Griffiths -- synthesis of ice flow directions from erratic trains and other evidence.

Friday, 17 February 2012

Stonehenge Laser Scanning Project

I found this info on the web:  EH has been assessing tenders for a Stonehenge laser scan -- archaeological analysis.  Value -- up to £15,000.  To be completed in 2 months.

http://www.tendersdirect.co.uk/Search/Tenders/Expired.aspx?ID=%20000000003548306&sect=A081&cat=20&Source=Categories

Do any of our spies out there have anything to share?  Not sure how this project is supposed to move forward the earlier work reported here:

http://www.stonehengelaserscan.org/
http://www.bbc.co.uk/news/science-environment-12688085

Ancestors return to Stonehenge?

From Julian Richards's web site / blog.  Mostly he's touting for business (well, we all have to make a living somehow) but he also says this:

............I will be back on TV again in the Spring with a new series on BBC 4 called Meet the Ancestors – revisited - there are more details in the TV and Radio section. So perhaps I can return to calling myself an ‘archaeologist, writer and broadcaster’ as I am certainly still (and always will be) an archaeologist and I’m also still writing - have a look in Books.
Inevitably I’m still fascinated by Stonehenge, as I think you may be able to tell from my Diary - lots of talks to groups around the country as well as some weekend outings next year for various specialist tour operators. This is why I will be adding a new Stonehenge section in the website soon so that I can keep everyone up to date with what’s going on in and around that fantastic site.

site.http://www.archaemedia.net/new/

It will be interesting to see whether Julian has noticed the debate about the transport of the bluestones -- and whether he gives any credence at all to the idea that glaciers might have had something to do with it.

Am I right in thinking that Julian writes the EH official guidebook to Stonehenge?  He certainly wrote the old edition I have on my bookshelf........

The Enigma of Achill-henge

Photo: Ronan.  Achill-henge on the island of Achill -- a structure pregnant with symbolism.....

A nice story from the BBC about the ongoing saga of Achill-henge.  Nobody seems too sure what it is, why it was built, and what it signifies. Anyway, it seems to represent -- in a roundabout sort of way -- disrespect for the planning system, anger against authority, and a desire to leave a mark on posterity.  Lessons for those of us who happen to be rather keen on Stonehenge?  Well, maybe that old thing was also built by some disaffected tribe (or maybe some teenage gang?) determined to do their own thing -- and obsessed with  building a folly or an enigma which actually had no meaning at all, but which would be guaranteed to upset their elder statesmen and to keep people guessing and debating for thousands of years into the future.......

Achill-henge: A monument that divides Ireland

16 February 2012
By Kieran Cooke BBC News
http://www.bbc.co.uk/news/magazine-17034637

Ireland has plenty of ancient settlements and monuments. But on Achill Island, off the far west coast - up a mountain and in the middle of a bog - sits a different kind of monument that locals are calling Achill-henge.  The wind is so strong, just opening the car door takes considerable effort. A spitting downpour of hail hits the flesh like shards of glass.  Balancing on one foot in a gale to put on waterproof trousers is not a good idea. I am blown, hopping, along the rough track, eventually toppling into a soft - and very wet - patch of bog.

Achill Island is about as far west in Europe as you can go: "From here it's next stop New York," said the man in the bar.  On a bright summer day its rolling boglands and towering cliffs have a haunting, majestic beauty. But on a winter afternoon, with a force 10 gale blowing, Achill really does feel like the end of the road, the edge of the earth.  Leaning into the wind, I struggle for about 1.5km (1 mile) up the mountain, its top covered in a thin layer of snow, like sugar powder sprinkled on a cake.  And then, rising out of the bog as if it is some science fiction creation, it comes into view - a massive circular concrete construction of 30 columns, each more than 4m (13ft) high.  The edifice, a very modern looking coliseum, is topped by a ring of stone: in all the construction is more than 100m in circumference.

Taking their cue from ancient Stonehenge in southern England, locals have been quick to name the site Achill-henge.  Only a short time after it was built, roughly-made signs now guide the adventurous visitor up the slippery mountain path.  A local developer with a grudge against the authorities is responsible for Achill-henge.  In the past, he has driven a cement mixer into gates of the Irish Parliament to protest about what he sees as the politicians' inept handling of the financial crisis.

I struggle up on to a pile of stone and wet earth to take a picture.  What is visible through the rain-soaked lens is peculiar, alien and definitely mysterious.  To some, it is Ireland's latest tourist attraction. To others, yet another example of developers' wanton butchery of the Irish landscape.

The hail has gone but another storm is galloping in from the Atlantic. In between the downpours, the high cliffs in the distance are lit by rays of sunlight. You feel the weather here in every fibre of your being. It is desolate.  Achill has always been a place of leaving. In one area, a whole village stands deserted - a relic to those who left during the mid-19th Century famine.  A railway once ran from Achill all the way east to Dublin. Each summer teams of locals would leave to go picking potatoes in Scotland and England.

During the recent boom, years of the so-called Celtic Tiger, people did return to live on what is Ireland's largest island. Now, what with financial bail-outs and the economic downturn, emigration has once again become a fact of life.

There are varying opinions about Achill-henge: even those virulently opposed to the construction admit it is a considerable feat of engineering - built over a weekend in November without planning permissions - by a team of workers hauling giant concrete slabs up the mountain side and sinking them in the bog.  "It would have taken the council five years to do anything like that," says one local.

Achill has always had a reputation as a wild place, where the rule of law does not always apply.  Over the years, writers and artists have been drawn to the islands' rugged landscape, the clarity of its light - and its tempestuous storms.  Graham Greene spent time here in a tumbledown house, writing and pursuing his then lover, a rich and eccentric society beauty.  The German writer Heinrich Boll was a frequent visitor - it was a place, he said, where you could play truant from Europe.  What, I wonder, would they have thought of Achill-henge?

Orders to demolish the construction have gone unheeded.  Strangely, the man responsible for the project has said little about what Achill-henge is, what it represents or exactly what he intends to do with it.  A poll in a local newspaper found that most people feel Achill-henge should be left standing.  Some see it as a place of contemplation, or even as a daring art installation.  It is causing plenty of confusion. One man summed up the general feeling. "It is meaningless - in a way - so each of us can put our own meaning on it."

The Music of the Spheres



A new article in the Guardian -- another in a series of stories about the auditory characteristics of the old ruin.  All very etherial.  Well, it keeps people out of mischief.  It's interesting that Prof TD, when asked, said he was not very convinced by the new theory -- but took the opportunity to express his ongoing belief in another theory which is (to put it mildly) equally unsupported by facts on the ground. 


Stonehenge was based on a 'magical' auditory illusion, says scientist

The layout of Stonehenge matches the spacing of loud and quiet sounds created by acoustic interference, new theory claims

Ian Sample, Vancouver
guardian.co.uk, Thursday 16 February 2012


The Neolithic builders of Stonehenge were inspired by "auditory illusions" when they drew up blueprints for the ancient monument, a researcher claims.

The radical proposal follows a series of experiments by US scientist Steven Waller, who claims the positions of the standing stones match patterns in sound waves created by a pair of musical instruments.

Waller, an independent researcher in California, said the layout of the stones corresponded to the regular spacing of loud and quiet sounds created by acoustic interference when two instruments played the same note continuously.

In Neolithic times, the nature of sound waves – and their ability to reinforce and cancel each other out – would have been mysterious enough to verge on the magical, Waller said. Quiet patches created by acoustic interference could have led to the "auditory illusion" that invisible objects stood between a listener and the instruments being played, he added.

To investigate whether instruments could create such auditory illusions, Waller rigged two flutes to an air pump so they played the same note continuously. When he walked around them in a circle, the volume rose, fell and rose again as the sound waves interfered with each other. "What I found unexpected was how I experienced those regions of quiet. It felt like I was being sheltered from the sound. As if something was protecting me. It gave me a feeling of peace and quiet," he said.

To follow up, Waller recruited volunteers, blindfolded them, participants to sketch out the shape of any obstructions they thought lay between them and the flutes. Some drew circles of pillars, and one volunteer added lintels, a striking feature of the Stonehenge monument.

"If these people in the past were dancing in a circle around two pipers and were experiencing the loud and soft and loud and soft regions that happen when an interference pattern is set up, they would have felt there were these massive objects arranged in a ring. It would have been this completely baffling experience, and anything that was mysterious like that in the past was considered to be magic and supernatural.

"I think that was what motivated them to build the actual structure that matched this virtual impression. It was like a vision that they received from the other world. The design of Stonehenge matches this interference pattern auditory illusion," said Waller, who described his research at a meeting of the American Association for the Advancement of Science in Vancouver.

"It's not a complete structure now but there is a portion of the ring that still has the big megaliths arranged in the circle. If you have a sound source in the middle of Stonehenge, and you walk around the outside of the big stones, what you experience is alternating loud and soft, loud and soft, loud and soft as you alternately pass by the gaps and the stone, the gaps and the stone," he added.

"So the stones of Stonehenge cast acoustic shadows that mimic an interference pattern."

Waller argues that his findings are not mere coincidence and says local legend offers some support for his thesis. Some megaliths are known as pipers'  stones, while stories tell of walls of air forming an invisible tower, and two magical pipers that enticed maidens to dance in a circle before they turned to stone.

Stonehenge was built in several stages, with the lintelled stone circle constructed around 2,500 BC. The site was originally a burial ground, but may also have been a place for healing.

In 2009, Rupert Till, a music expert at Huddersfield University, used a full-scale replica of Stonehenge and computer analyses to show that repetitive drum beats and chanting would have resonated loudly between the standing stones.

Timothy Darvill, professor of archaeology at Bournemouth University, said that while sound played an important role in events at Stonehenge, the monument was probably not designed with acoustics in mind.

"The main structure is a replica in stone of what was normally built in wood," he said. "They used the same techniques. The positioning of the main components is all about the construction of a framework, a building if you like, as the setting for ritual adventures that included the use of the bluestones brought over from Wales."

Monday, 13 February 2012

Pembrokeshire prehistoric sites

Thanks to Chris for drawing my attention to this.  Somehow I had missed it, although it has been out for almost 2 years.  It's a quite comprehensive survey of the Neolithic and Bronze Age features (and some others besides, of uncertain age) centred on two areas -- around Carningli near Newport, and around Carn Alw on the northern flank of the Preseli ridge.  Both areas are very rich in remains.

This is my sort of archaeology -- careful field recording, good photos and maps, and sufficient site detail to whet your appetite.  And NO wild speculation or fairy tales...........

Citation:  DYFED ARCHAEOLOGICAL TRUST REPORT NO. 2009/63 PROJECT RECORD NO. 96851
March 2010
SCHEDULING ENHANCEMENT PROJECT 2010:
PREHISTORIC SITES FIELDWORK – PEMBROKESHIREBy
F. Murphy, M. Page, R. Ramsey and H. Wilson

Thoroughly recommended.  Do a Google search and you'll be able to find and download the PDF.  These are sample entries from the Gazetteer:

PRN 96872  NAME CARN DDAFAD LAS
TYPE CORN DRIER, CHAMBERED TOMB  PERIOD Neolithic; Medieval; Post
Medieval
NGR SN1456533344
CONDITION Damaged  STATUS CL , NPP  FORM Earthwork

SUMMARY
A 'key hole' shaped stony earthwork situated on a north facing gentle slope of
Mynydd Preseli at 250m above sea level. It is possibly the remains of a corn drier
and associated with or part of the nearby settlement PRN 11523.

LONG DESCRIPTION
A 'key hole' shaped stony earthwork situated on a north
facing gentle slope of Mynydd Preseli at 250m above sea level. The earthwork is
aligned N-S with the circular 'hole' upslope to the south. Overall it measures
c.11.0m N-S by 6.5m E-W and the circular 'hole' shaped bank measures c.4.5m
in diameter. The earthwork stands at its highest point at just over 1.0m high. The
banks are c.0.8-1.0m wide and are hard to define to the N, where it is more a
tumble of stone protruding through the turf, although there are several larger
upright stones that could have been part of the flue entrance. At the southern
'hole' shaped end the bank surrounds a circular depression approximately 0.4m
deep. It appears to be part of or associated with the surrounding settlement PRN
11523. This earthwork stands out in the landscape due to its size and make-up.
During the 2009 fieldwork similarities between this earthwork and those recorded
just north of Carn Alw (PRN 11540-1) and to the scheduled post medieval corn
drier found further north again of Carn Alw (PRN 28275, SAM PE 466), were
perceived. However, in their 2003 Spaces Project report Darvill, Morgan Evans
and Wainwright published a survey of this particular earthwork. They are of the
opinion that it is a prehistoric chambered tomb that has similarities with Bedd yr
Afanc scheduled chambered tomb (PRN 1032, SAM PE 122) that lies
approximately 3.5km to the west. It is such an unusual earthwork that it is not
surprising that there is such a range of interpretations, and only excavation may
answer the question of what it is. In close vicinity to this earthwork are at least 3
clearance cairns at SN14563337, SN14563338 & SN14533344. They are low
earthen stony mounds with an average diameter of c.4.0m. FM & HW June 2009.

-----------------------
PRN 1487  NAME CARN INGLI
TYPE ENCLOSURE  PERIOD Prehistoric
NGR SN06283797
CONDITION Damaged  STATUS CL , NPP  FORM Earthwork

SUMMARY
A large roughly oval enclosure situated on a north facing promontory on the
northern slopes of Mynydd Carningli, with impressive views in all directions.

LONG DESCRIPTION
This is a roughly oval enclosure. It is situated on a north
facing promontory at 200m above sea level. It is about 100m E-W by 80m N-S
and is defined on the west by a curving stretch of bank and ditch c.60.0m long,
and elsewhere only by natural scarps that enclose an area of level ground. The
bank is c.0.9m high and the ditch 0.6m deep. There are no apparent internal
features. The ground falls away on all sides but the south-west, and where it falls
away steepest on the north there appears to be evidence of terracing or scarping.
It has the appearance of an unfinished defended enclosure, and later than the
surrounding prehistoric features. However, all the surrounding sites respect it and
the field boundaries do not pass under the banks or cross its internal area which
may suggest it is contemporary rather than later in construction. FM & RR May
2009 Banked and ditched earthwork enclosure of unknown purpose and date. RPS
August 2001

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

If you want to find these sites (and all the others!) go to this web site:
http://gridreferencefinder.com/
Wait for the map to load, and then type the grid ref into the search box.




Sunday, 12 February 2012

The other Bedd yr Afanc legend



Are you sitting comfortably?  Then I'll begin...... this is the better-known version of the Bedd yr Afanc legend.  The stream referred to here is of course the very one that flows past Craig Rhosyfelin, a bit further downstream.

Not  far  from  Brynberian there is  a  most  unusual  burial chamber  on  the bleak moorland. It is a long,  low  gallery  chamber which is said to have similarities with some of the Neolithic  burial chambers  of  Ireland dating from about 2500 BC.  There is no  other burial  chamber like it anywhere else in Wales.  It is shaped like  a wedge,  but along the centre is a double row of standing stones about 35 feet long. It is called Bedd-yr-Afanc,  which may  be translated as "Monster's Grave".  However, some  authorities believe that the word "afanc" originally meant "dwarf", whereas  in modern Welsh it means a beaver.

According  to  a very old legend there was  once  a  terrible water  monster  which  inhabited  a deep  pool  in  the  stream  near Brynberian  bridge.  It  caused great fear in  the  hearts  of  local people, stealing sheep and other animals and laying waste the country round about. At last it was decided that the afanc must be slain, and so  a plan was set in motion. It was known from ancient history  that water  monsters could not resist the sight of a fair maiden,  so  the fairest  girl in the village agreed to be used as a bait. At  dusk  a powerful team of oxen was brought to the vicinity of the pool,  while the  men  of the village set loops of strong iron  chains  along  the river bank, with the chains connected to the oxen.

Later,  when  the full moon was high in the sky,  the  locals waited  with baited breath for the afanc to appear, as it always  did on the night of the full moon.  The brave girl sat some way from  the river  bank,  looking very beautiful in the moonlight, and with  her long  hair falling about her in waves.  She felt  extremely  nervous, for  she  knew that long ago, according to legend, another  afanc  in North  Wales had torn off the breast of a maiden such as she when  it was captured.  At last the monster emerged from the pool. Seeing  the girl,  it was immediately entranced, and lumbered towards her  across the  dewy grass of the river bank. She waited till the last  possible moment,  and  then with a scream she fled. At the same time  a  great shout went up from the men who had been hiding nearby, and the  oxen strained on the iron chains. The chain loops on the grass closed, and the  afanc was caught around its legs.  With a roar of fury it  tried to  return to the sanctuary of its pool, and as it thrashed about  it temporarily  reached the water.  But the oxen were immensely  strong, and  as they were driven by their masters there was no escape for  the afanc.  Bit by bit the chains were drawn tighter about its body,  and bit  by  bit it was hauled out of the river and up  the  river  bank.  Then all the men attacked it, with whatever weapons they could muster -- axes, sickles, spades, scythes, forks and pointed spears.

At last, after a mighty battle, the bloodied monster lay dead on the grass.  A rousing cheer echoed around the moonlit countryside, and as the news spread people came from near and far to see the  dead beast. Nobody slept much that night; the ale flowed freely,  and  the celebrations went on until daybreak.  Then, in the morning, the  oxen hauled  the  dead monster up onto the moor. In a suitable  place  the chains were undone, and the creature was buried in a great tomb  made of  slabs of rock from the mountain.  It was covered with stones  and earth,  and  from that day to this the site has been called  Bedd  yr Afanc.


The Legend of Bedd yr Afanc



Since some of the faithful followers of this blog have a soft spot for fairy tales and the like, it's worth mentioning that Bedd yr Afanc has quite strong folk traditions attached to it.  Not sacred -- strictly secular.  In Welsh mythology the "afanc" (translated as "beaver" today) was a fearsome water monster which terrorised the countryside and devoured cattle and other farm animals.

There are two main legends surrounding this strange and ruinous gallery grave.  One has it that the Afanc, dwelling on the Preseli slopes somewhere above Brynberian, ravaged the countryside, committing such depredations on the local livestock that a consultation of the wisest folk was held to devise some means of getting rid of him. They decided to slay him by a trick. A deputation was sent to him to ask him to dig a well for the people. This he agreed to do, and forthwith began working furiously. When he had dug to a great depth ("over one hundred yards" said one relater) the people above tipped into the hole he had made a big load of "white stones" (presumably quartz pebbles) which they had collected on the mountain-sides, intending to crush him to death. But next morning they found him still digging, and were informed by him that there had been a rather heavy snowstorm on the previous day, which he had found to be but a minor irritation.  Thus they were unable to do away with him; and he continued as before, eventually "dying a natural death", after which "he was buried on the hill side" between Hafod and Brynberian, "and his tomb may be seen to this day". 

This story was collected by T.R.Davis (past Schoolmaster of Newport School) and included by him in original Welsh in his prize essay on N. Pembrokeshire Folklore (MS. Maenchlochog, 1906). He heard it from shepherds and cottagers in the Precelly district.

This version of the myth was posted by Rhiannon on The Modern Antiquarian:

http://www.themodernantiquarian.com/site/2362/beddyrafanc.html

Saturday, 11 February 2012

South Wales -- glacier battleground

I'm increasingly intrigued by the pattern of glaciation in South Wales, since this does have a direct bearing on the transport of erratics from Pembrokeshire and the South Wales valleys towards Stonehenge.  Chaos!!

The top map shows approximately what happened during the latest (Devensian) glaciation, with the drainage routes of Welsh glaciers and ice streams flowing more or less radially from the centre of the Welsh ice cap and coming into contact in the W, N and NE with the ice of the Irish Sea Glacier.  On the south and SE flanks of the ice cap it's generally thought that there was no contact with Irish Sea ice at this time, since the Irish Sea Glacier was of more limited extent.  However, the yellow line, showing the edge of the Irish Sea Glacier, is inaccurate -- the ice certainly extended further to the E and S than shown, especially in the area of the Pembrokeshire peninsula.

The lower map shows the "battleground" between the Welsh glaciers flowing broadly southwards, and the Irish Sea ice coming in from the west.  We still do not know how big all these glaciers were during the Anglian and other earlier glaciations, and what the precise sequence of expansions and contractions might have been.  Henry Patton in Aberystwyth is currently modelling the Devensian Welsh Ice Cap -- his work is very interesting, but it is an inadequate model in that it does not incorporate the pressure exerted by Irish Sea ice in some sectors at certain times.  That complication will no doubt come in at a later stage in the modelling......

What cannot be doubted, from what we know about erratic transport routes and till characteristics, is that large stones and till components have been moved about many times, sometimes being carried southwards and even westwards by Welsh Ice before being picked up and moved back again -- with a general direction of NW towards SE -- by the massive glacier pressing in from the Irish Sea, Cardigan Bay and St George's Channel.

So we have Irish Sea components and components from the Coalfield valley glaciers on the Vale of Glamorgan and on Gower, and a perfectly adequate mechanism for the flushing out of sandstone blocks from the ORS Senni Beds  towards Carmarthen Bay, and for this material to be moved eastwards later, as the Irish Sea glacier builds up to its maximim size.

Of course, the total "journey time" for a large block of stone being moved from A to B may in reality have been several hundreds of thousands of years, spanning several glacial episodes.

The general rule in all glaciations of this rather complex area is that the valley glaciers will have grown very large, and been very active, in the early stage of every glaciation,  to have been displaced or "muscled aside" later on by Irish Sea ice coming in from the NW and W, as shown on the maps.  Generally ice sheets and ice caps in the mid-latitudes collapse very quickly, which means that there might not have been any "late glacial valley glacier expansion episodes" in these early glaciations.  But we cannot be sure about that until much more research is done.

Pembrokeshire's last glacier

My thanks to Jonathan Lee and Aberystwyth University for more amazing images of the Preseli area -- created using a technique called digital stereo aerial photography  -- representing attitudinal changes to an accuracy of 2m and then creating a sort of 3D effect through the application of "false lighting and false colour."  Notice that the light falls from reasonably high in the NE -- which it almost never does in the UK in reality.  That's a technique used on traditional relief maps for many years -- it so happens that the eye and the brain manage to interpret the shape of the land more accurately than if the light falls from other quadrants (which causes an inversion of relief, causing peaks to show up as pits and vice versa.)
More info here:
http://www2.getmapping.com/Products/Getmapping-Height-Data

At any rate, this is a fragment of a larger image which shows the site of Pembrokeshire's last Ice Age glacier, in Cwm Cerwyn, immediately to the east of Foelcwmcerwyn or Preseli Top.  The headwall of the "incipient cirque" is aligned towards the ESE -- which is unusual, since broadly south facing hollows are supposed not to be good places of cirque development in the Northern Hemisphere.  Most cirques have a preferred orientation of NE.......

But here, in the Younger Dryas, around 10,500 years ago, there was obviously sufficient precipitation coming in from the west to collect in the lee of Foelcwmcerwyn to create a small cirque glacier that survived for a few centuries.  If you look carefully you can see a little hummock of moraine on the floor of the depression -- and if you examine that on the ground, you can find striated stones and boulders.......

Incidentally, this glacially steepened slope is just about the only place on Preseli where you can actually fall off, if you are not careful!

Garnwen, Brynberian

I found a strange reference to Garnwen, Brynberian.  Here, on the south side of the road and about a km from Craig Rhosyfelin, there is a "record of a possible barrow."  The grid reference is SN112351.  Apparently there is no trace of any archaeological feature, but there is a scatter of white quartz fragments -- which presumably led somebody to think of Newgrange and a possible disappeared round barrow.  Of course, it may simply be that in this area there is an outcrop of Fishguard Volcanics with a particularly rich concentration of white quartz veins........

Not sure if Richard Bevins and his colleagues have looked at this site during their field sampling of the local volcanic rocks.......

Bedd yr Afanc

Bedd yr Afanc gallery grave, near Brynberian, Pembs (photo:  acknowledgement to Sem)

Somebody asked recently what the significance of Bedd yr Afanc might be,  given that it lies less than 2 km from Craig Rhosyfelin.  As a geomorphologist who thinks Craig Rhosyfelin has no archaeological significance whatsoever, I think these locations are purely coincidental.

All we know about Bedd yr Afanc is that it is a ruinous gallery grave or passage grave with certain similarities with Irish or Scottish gallery graves, located on a low mound in a very boggy and open landscape. What we have is a single long gallery, without any side chambers.  It's the only grave of this type in Wales.  It's in a very beautiful location -- one of my favourites.

What we see today is a row of paired stones, nearly all of them less than a metre high -- with some traces of fallen capstones.  The gallery is just over 10m long.  One would expect there to be more capstones present (maybe at least ten of them) -- and some have suggested on this basis that the building project was never completed.

Did it ever look line Newgrange or La Hougue Bie?  It may have been the builders' intention that the passage should look like this:


 This is the interior of La Hougue Bie on Jersey Island -- and this is the exterior, with a rather more recent church plonked on the top of the mound:


Clearly the ambitions or resources of the builders of Bedd yr Afanc were more modest than those who inhabited Jersey and Brittany.  But does the presence of Bedd yr Afanc suggest that there was a thriving Neolithic megalithic culture in this area at about the time when Stonehenge was built?  A culture, yes, but was it a THRIVING one?  The only other features in the area are the Waun Mawn standing stones -- which again seem to me (see previous posts) to have represented ambition but not a lot in the way of capacity or competence to complete a circle-building project.

It seems to me that some of the tribes or family groups on the north side of Preseli were maybe tapping into megalithic building traditions carried into the area from outside, but were not numerically strong enough to carry them through.  Other groups were clearly quite competent enough to build Pentre Ifan burial chamber and the other cromlechs in the "Newport Group" -- but of course we know nothing about whether there was cooperation or rivalry between the groups involved in all these projects, and the various structures may also differ quite widely in age.

Friday, 10 February 2012

Even more about the Stonehenge rhyolites



Rob Ixer has kindly sent me a PDF of the latest paper in the series of geological publications homing in on the rhyolites in the Stonehenge debitage. 

This paper examines the evidence for rhyolite fragments that might have come from sites other than Craig Rhosygfelin, using petrography and "whole-rock geochemistry."  The abstract is below.  The main conclusions of the research are that there are no traces thus far of any fragments from the Sealyham Volcanic Formation (which outcrops to the south and west of the Preseli Hills; and that of those fragments which have come from the Fishguard Volcanic Series the Craig Rhosyfelin outcrops are by far the most important sources.  Other sites thought in the past to have been source sites for rhyolite fragments -- namely Carn Clust-y-ci and Carn Lwyd near Newport -- are not now considered to have provided anything to either the orthostats at Stonehenge or to the debitage.  Then the authors say:  "Nevertheless, the possibility still exists that all of the dacitic and rhyolitic bluestone lithologies can be sourced in outcrops of the Fishguard Volcanic Group, in the tract of country between Fishguard and Crymych. If this indeed proves to be the case it will undoubtedly influence the location of future archaeological excavations to determine whether there exists evidence of anthropogenic activity in working particular outcrops or, in the absence of such evidence, whether entrainment and
transport by ice remains a viable alternative for the transport of the bluestones to the Stonehenge landscape.
"

This is all very interesting to those of us who have an interest in the geology -- but we do need to bear in mind that there is a strong sampling bias here, both at the Stonehenge end and in North Pembrokeshire.  Attention is focussing on the Fishguard Volcanic Series, and other sources for orthostats, stumps and fragments may well be found as work continues. These might even be from the North Pembrokeshire coast or on the Pen Caer Peninsula.  As the authors point out, their conclusions are still based upon a relatively small data base.  Much material still remains to be provenanced.  More publications are promised -- watch this space....  and when the rhyolites are sorted out, there is a great deal more to be done on the dolerites and sandstones.

 ----------------------------------------------
Provenancing the rhyolitic and dacitic components of the Stonehenge landscape bluestone lithology: new petrographical and geochemical evidence

by Richard E. Bevins, Rob A. Ixer, Peter C. Webb, John S. Watson
Journal of Archaeological Science 39 (2012) 1005-1019

ABSTRACT
The source of the bluestone component found in the Stonehenge landscape has long been the subject of great interest and considerable debate. The bluestones are a mix of lithologies, the standing orthostats being predominantly dolerites, variably ‘spotted’, with only four of them being of dacitic and rhyolitic composition and the Altar Stone being sandstone. However in the 1920s the spotted dolerites were sourced to outcrops which comprise tors in the summit regions of the Mynydd Preseli in north Pembrokeshire, west Wales. There were also speculations about the possible sources of the dacitic and rhyolitic components, ideas which were elaborated on in the early 1990s when the original petrological provenancing was supplemented by whole-rock geochemical analysis. Most recently, new petrographical investigations have been combined with zircon geochemical data to determine the possible source of one type of rhyolite, the so-called ‘rhyolite with fabric’, found abundantly as débitage in the Stonehenge landscape (but not composing the four orthostats) to outcrops in the vicinity of Pont Saeson, especially a large craggy outcrop called Craig Rhos-y-felin, located in low ground to the north of the Mynydd Preseli. In order to test this provenance whole-rock geochemical analysis has been undertaken on samples of débitage from the Stonehenge landscape and from the Pont Saeson area, including Craig Rhos-y-felin. These data are then compared with other new and existing geochemical data for dacitic and rhyolitic lithologies recovered from the Stonehenge landscape, including the four orthostats, as well as geochemical data from outcrops of the same lithologies from the two main volcanic horizons exposed across north Pembrokeshire, namely the Fishguard Volcanic Group and the Sealyham Volcanic Formation, both of Ordovician age. This study concludes that previous, 20th century, attributions of provenance to a number of dacitic and rhyolitic outcrops in the north Pembrokeshire have been in error whilst the new data for the Pont Saeson rhyolite accords well with elemental contents recorded in the ‘rhyolite with fabric’ lithology from the Stonehenge landscape débitage. This study therefore endorses the proposal that the Pont Saeson area is indeed the source of the ‘rhyolite with fabric’ lithology recovered from numerous sites in the Stonehenge landscape, and is the only reliable provenance for any of the dacitic and rhyolitic bluestone material collected to date. It also serves to endorse the use of zircon chemistry as a provenancing tool in archaeopetrological investigations.

The meteorite -- another "blau stone"?



Some time ago on this site, I reported receiving a paper from Geoff Kellaway,  in which he argues that the bluestones were never described as BLUE stones by the early visitors to Stonehenge, but that in the Middle Ages (ie around the time of Geoffrey of Monmouth and later) they might have been referred to in Ango-Saxon as BLAU stones — with the word “blau” meaning striking, different, or of unusual or striking appearance.  I thought that rather interesting......

Of course, this would make sense, since the stones are not actually blue at all — no matter what people might pretend, they are not that different in colour from the sarsens. But it’s intriguing to think that from an early stage people might have recognized them as simply DIFFERENT.

There is of course a tendency for people to see different, unusual, or striking stones in the landscape and want to collect them.  How many of us have done just that when collecting stones for our garden rockeries?   I think it's perfectly reasonable to suggest that when the Neolithic people living on Salisbury Plain wanted to put up the early stone settings at Stonehenge, they gathered up as many stones as they could find, showing particular interest in any stones that were "different" from the common sarsens which were widely distributed across the landscape.  Maybe they even invested these "different" stones with magical or sacred significance -- with those special qualities entirely unrelated to source of origin or distance carried.  I agree with many others who have suggested that the builders of Stonehenge did not have a clue where the bluestones had come from.

So a meteorite lying about in the landscape, or a Boles Barrow bluestone boulder, or even a piece of elongated bluestone suitable for use as a lintel later on -- all these were rather attractive things to collect, since they were different enough to be invested with status or significance.

Even more about the meteorite

 Extract:
"A document trail has been initiated which provides new and
verifiable information about the terrestrial provenance of the
meteorite associated with Lake House. The latest findings will be
presented together with an up-to-date probability/possibility
assessment of the place of first collection and hence the site of
the fall."
Does anybody know anything more?

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

EVALUATION OF VARIOUS HYPOTHESES RELATING
TO THE LOCATION OF THE FALL AND THE
SUBSEQUENT HISTORY OF A LARGE METEORITE
LATELY RECOVERED IN WILTSHIRE, UK
C.T. Pillinger and J.M. Pillinger. Planetary and Space Sciences
Research Institute, The Open University, Milton Keynes, MK7
67AA, UK. c.t.pillinger@open.ac.uk

Introduction:
A large, 60kg, weathered meteorite was
reported to have been in the UK for at least 60 years when it was
taken to the Natural History Museum, London, twenty years ago.
Previous to 1991, eye witness and photographic evidence
demonstrate that it rested for many years near to the front door of
an imposing country house in Wiltshire. It was reputed to have
been either brought to the UK or otherwise collected locally by Lt
Col Frederick George Glyn Bailey in the early twentieth century.
The descendents of FGG Bailey have made the specimen
available and encouraged a study to ascertain more information
about the meteorite before arranging for it to be on permanent
local public display. The meteorite is described in an
accompanying abstract.
The presence of a meteorite of unknown terrestrial
provenance offers a considerable challenge. Whilst a scientific
examination [1] can offer some information, much depends on an
exhaustive examination of contemporary documents. Some while
ago we were able to piece together a detailed account of the
circumstances surrounding the fall of the Wold Cottage meteorite
to show it should not be considered as just any old ordinary
chondrite [2].
Results: The life and times of Lt Col FGG Bailey have been
researched thoroughly in order to highlight any possible links he
may have had to a meteorite find either in the UK or the rest of
the World. The meteorite is inextricably linked to the house
where it was located for so many years: Lake House. Thus the
history of the Lake House Estate, the house, its previous
occupants and their associates, including their interests and
scientific aptitude, have also been studied in an attempt to
establish the earthly provenance of the specimen.
Several hypotheses have been considered to account for the
presence of the meteorite in Wiltshire. Necessarily these
hypotheses revolve round the people who could conceivably have
had an involvement in the meteorite’s history on Earth.
Questions regarding whether they might have had the motivation,
opportunity and capability to recognize a meteorite have been
considered. Even if they did, they would have needed the
resources to move such a large stone and have the desire to
collect and display it.
A document trail has been initiated which provides new and
verifiable information about the terrestrial provenance of the
meteorite associated with Lake House. The latest findings will be
presented together with an up-to-date probability/possibility
assessment of the place of first collection and hence the site of
the fall. The work reported here may offer some pointers to
others searching archive material for reports connected to
meteorite related events.

References: [1] C.T. Pillinger et al., this volume. [2] C.T.
Pillinger and J.M. Pillinger Meteoritics and Planetary Science 31,
589-605 (1996)