The West Angle Enigma (2): the silt and clay series

 West Angle Bay, near the mouth of Milford Haven.  The main exposure is at the back of the beach, between the car park and the sharp bend in the cliffline near the bottom edge of the photo.  The position of the old brick pit is now very difficult to discern from the air.

The "ridge" of interglacial and glacial sediments exposed in the southern part of West Angle Bay.  The beach is to the left and the brick-pit is to the right.

The sands, silts and clays which overlie the raised beach at West Angle, and which lie beneath the reddish till, are so unusual that they have caused intense (and sometimes acrimonious!) debate among geomorphologists and geologists.  Dixon (1921) referred to them as "loams" but that term is misleading since it is conventionally used for a sandy or silty soil, which implies a period of subaerial evolution beneath a plant cover.  There is certainly some evidence (in the form of a peat bed) of vegetation accumulating and growing -- but it would be a mistake to simply assume that all of the sediments in this sequence were accumulating at the ground surface.  They are very fine-grained, and many researchers have concluded that some of sediment accumulation was beneath water, either in a lacustrine, marshy or estuarine environment. So let's simply refer to this sequence of quite variable sediments as the "silt and clay series".

First, the base of the series.  According to my observations, and those of David Unwin, there are ferruginous cross-bedded sands and gravels above the raised beach.  These are generally less than 1 m thick, but Unwin interpreted them as "dune sands" and I am now inclined to agree with him.  (I originally thought that they might be beach sands laid down on top of the pebble beach during the course of a marine transgression, but I now think that evidence in support of this hypothesis is in short supply.......)  Another interesting fact is that stony grey silts up to 40 cms thick seem to be associated with these sands and with the upper part of the raised beach facies.  This suggests that at the end of the raised beach episode (the Ipswichian interglacial?) sea-level might have dropped slightly, or else there was some other environmental change.  This led to the accumulation of slope deposits or rockfall materials and pre-existing sediments on the valley side, with colluviation extending as much as 30 m from the valley side out onto the valley floor.  Possibly a sand dune system developed on top of the raised beach with a dune slack behind it.  Colluvial materials (incorporating angular rock fragments and also raised beach pebbles and shingle) were then interdigitated with sandy dune materials and with peats, silts and clays in a freshwater environment.

Two examples of flooded dune slacks in England.  In each case, the wetland is trapped behind a sand dune belt at the back of the shoreline.  In West Angle the dry valley has probably existed for hundreds of thousands of years, so without a river to breach the dune belt there are perfect conditions for semi-permanent lakes to exist during interglacial periods, so long as the water table remains high.  There may well have been intermittent tree cover -- this is suggested by the pollen and plant remains in the sediments.

The exposed section at point H, about 25 m away from the rocky valley side at West Angle. Here the top of the raised beach is slightly above the level of the present-day pebble beach.  Above it there is a layer of ferruginous cross-bedded sand, then a thin gravel layer, and then about 30 cms of grey colluvium with angular fragments, and then a peat layer shown with cross-hatching. This has a maximum thickness of c 45 cms.  Above that is the grey silt and clay series, followed by the orange silt and clay series.  At this point the reddish till, sands and gravels are not represented.

Now to the peat and peaty silt layer.  Since this was first discovered it has caused great excitement, since interglacial peat beds in Wales are exceedingly rare.  It has always been assumed that it is linked in some way with the raised beach and with the silt and clay series, which also contains abundant plant remains.

 A more detailed section near cutting H, transposed from a photograph.  The main stratigraphic junctions are shown, together with the peaty silt and peat layer.

 The Silt and Clay Series.  Fragments of well-preserved oakwood, rootlets and leaves are found here and there, and Dixon (1921) referred to "plant fragments and occasional large pieces of wood."   In "Nature" journal in 1968 I reported the conclusions of Dr Ian Simmons and other Durham colleagues regarding samples taken from the sandy and silty layers just above the raised beach.   Ian showed that the pollen and plant remains are fully representative of an interglacial environment.  Quercus (35% of total tree pollen), Alnus (43%) and Corylus (42%) were the dominant constituents, with Pinus only moderately represented (13% of tree pollen).  Non-tree pollen accounted for 85 of the 343 pollen grains counted, with Gramineae, Cyperaceae and Filicales moderately well represented.  Other lesser plant pollen (eg Chenopodiaceae and Armeria) suggesting proximity to littoral conditions.  The vegetation was thus a mixed oak and alder forest with pine and hazel, with salt-tolerant plants close to the water's edge.  Carex, Juncus and other water plants point to an environment that included small open pools with patches of marsh and fen and carr vegetation.    Botanists who have examined my own evidence incline to the view that this was a fresh-water rather then a salt-water (estuarine) environment.

Other researchers tend to agree with this interpretation.  For example,  Bowen (1974) found Alnus tree stumps in a growth position on the surface of the "loam" and dated one of them to >35.5 ka.  This would suggest an Early or Middle Devensian (and possibly an Ipswichian) age for the silt and clay series.   Morey (1997) drew on the research of Stevenson and Moore (1982) and wrote as follows:

"..........Stevenson and Moore (1982) recorded the aquatic taxa, Sparganium, Potamogeton, Typha, Nuphar, Nymphaea and Polygonum amphibium together with Valeriana officinalis, indicating the presence of areas of open, fresh, water bordered by a tall herb- marsh community. Their data also indicate a regional flora with the trees and woodland species characteristic of a temperate (interglacial) environment........... Since estuarine muds deposited in a temperate environment typically contain a substantial fauna with forams, ostracods and small gastropods, as well as larger bivalves etc. the lack of marine fossils makes an estuarine origin for this unit appear unlikely and the earlier interpretations should be questioned. It seems more reasonable to interpret Unit 3 as an alluvial deposit characterised by pools of fresh water. Other taxa present, Hippophae, and Plantago maritima, could be derived from a surrounding dune community.  Stevenson and Moore (1982) also noted a record of Ruppia maritima by Turner, but the presence of a species which is usually associated with brackish pools does not conflict with this interpretation as a marshy valley among coastal dunes."

In 1973 Stevenson and Moore found the following sediment sequence:

Head deposits overlying:

Yellow/orange sandy silt
Grey/yellow sandy clay
Yellow/orange clay with abundant pebbles.
Apparently sharp hiatus
Stiff blue/grey clay with sandy bands at 106 cm. Organic sediments, laterally variable in nature were found within this unit, as was evidence of current bedding in the inorganic sediments.
Grey—brown silty clay. (with included Alnus wood layer). Organic remains become more abundant towards its base; especially obvious are wood fragments
Pebbles in a grey, sandy-clay matrix. Larger pebbles (up to 5 cm diameter) were concentrated in the lower layers.
Very fine white sand, cross-bedded
Very fine yellow sand with an iron-rich layer
Fine yellow and white sands, particles of larger size evident towards the base
Iron concreted, yellow and red sands
Coarse-grained yellow sands with hard bands of ferruginous, cemented material
Pebbly, raised beach deposits

Stevensen and Moore (1982) found four pollen assemblage zones in the silt and clay sequence, all dominated by temperate forest taxa -- so they were convinced that the climate throughout the whole sedimentary episode was temperate rather than glacial or periglacial.  They were inclined to suggest a Hoxnian interglacial age for this episode, but others (such as Campbell and Bowen in 1989) preferred an Ipswichian or Last Interglacial interpretation.

One interesting feature of the work by Stevenson and Moore is the presence of a "hiatus" in the pollen sequence in their Zone WA-2.  They suggest that there was an episode of extensive forest destruction, followed by secondary succession and woodland recovery, but resulting in a changed floristic composition. Such destruction could have resulted from flooding or erosion. The possibility of habitat disturbance as a result of factors associated with local fluviatile conditions is very real in this swamp-carr site. Marine incursion is also possible.

Another suggestion (and it is no more than that) is that towards the top of the sequence there is an increase in Pinus pollen and a decline in some other species -- possibly indicative of a "post-temperate" plant assemblage taking over from a truly interglacial one.  Does this represent the end of the interglacial and the onset of colder -- and eventually periglacial -- conditions?

 Stevenson and Moore pollen diagram for the silt and clay series.  Note that near the junction between the blue clay and the yellow clay there is a sharp decline in oak pollen and a corresponding increase in pinus pollen.  Does this indicate a cooling of temperature at the end of the interglacial episode?

In the absence of accurate dating for the sediments and their plant remains,  all we can say for the moment is that they seem to be linked with the raised beach, that they were probably laid down in a largely freshwater environment of pools and marshy patches, and that the accumulating sediments might have been protected from the open coast by a barrier of sand dunes.  The environment is an unusual one, in that the Angle Valley runs right across the peninsula  as a limestone "dry valley" containing no substantial stream.  This may explain why the circumstances for sediment accumulation here were not at all similar to those which prevailed in other valley mouth situations such as Abermawr, the Nevern Estuary, Newgale, and Goodwick.  But it's reasonable to assume that when the silt and clay series of sediments was accumulating, sea-level was not very much below that of the present day; if it had been, I assume that the water table on the valley floor would have been much lower, and that pools of standing water would not have survived in this vicinity for prolonged periods.  The suggestion of a sudden marine incursion (a tsunami?) high in the sediment sequence also indicates that the sand dune barrier might not have been very strong, and that through most of this chapter in the story, sea-level was at its "interglacial" or high-stand level.

This drone photo shows just how sheltered the head of the bay really is.  The sediment sequence is in the left foreground.  Very little is now left of the old brick pit.  It's easy to see how a dune slack situation might have developed here.

The West Angle enigma (1): the stratigraphy

Three photos of the drift cliff / main exposure at the back of West Angle beach.  As we can see, the vegetation cover has varied over the decades -- and every now and then it is "freshened up" by extreme winter storms.  If you are a geologist or a geomorphologist, what you see is partly a matter of luck.......

One of the most difficult sites in the British Quaternary is at West Angle, near the mouth of Milford Haven.  It is considered by all workers (and there are many who have published) to span a very large part of the Late Quaternary.  Some, including DQ Bowen, think that there are signs of TWO glacial episodes represented here, with glacial and periglacial deposits separated by a raised beach of probable Ipswichian (last interglacial) age.  In the early 1900's there was a clay-pit here, worked for clay which was used in an adjacent brick-making kiln, but following the closure of that operation the clay-pit has been abandoned and is overgrown, and the adjacent sedimentary exposures at the back of the beach have become degraded and very messy.  There are many slumps, and many places where human interference has destroyed the natural stratigraphy.  It's difficult to see what on earth the section looks like, let alone to decide what it all means.....

The earlier workers, including Leach and Dixon (1921) had the advantage of being able to examine the stratigraphy in the clay-pit.  They recorded the sequence as follows:

8.  Angular stony loam - head?  3 ft
7.  Sand with abundant rounded bedrock flakes (?!!) plus erratics (including one from N Pembs) -- 4 ft
6.  Well bedded gravel and sand -- 2 ft
5.  Buff laminated loam including erratics -- 5 ft
4.  Dark blue loamy clay with wood and plant fragments -- 5 ft
3.  Irregular loam, sand and fine gravel  - 3 ft
2.  Grey clay or loam -- 1.5 ft
1.  Clean buff sand -- 1 ft

This sequence has been mis-reported by other researchers to suggest that till was found in the pit beneath raised beach materials.  However, the Geological Survey surveyors were very experienced, and  they did not refer to the gravel and shingle (6) as a raised beach deposit; and neither did they refer to the grey clay and loam (2) as a glacial deposit.

Back in the 1960's and 1970's David Unwin, David Bowen and myself, all working independently with other fieldworkers, measured and described the site, and undertook excavations, but we all seem to have seen slightly different things!

When I organized excavations here in 1965, we managed to dig a couple of metres below present beach level, exposed the raised beach, and found just "basal sand" beneath it.  The sand acts as an aquifer, and is disturbed by flowing water -- so our trenches filled with water so quickly that we could not discern any structures.

David Unwin also described the raised beach, and showed its relationship with other deposits as follows:

David Unwin's sketch of the main exposure at West Angle (north part).  RB = raised beach.

David Unwin's section (south part)

David shows nothing beneath the raised beach deposit, and he shows a complex unconformity on one side of which is a reddish till (?) on which he undertook various fabric analyses.  I have not seen those results, and I don't think they were ever published.  There is one big mistake on the southern part of his sketch section, and that is his portrayal of all the beds as dipping southwards.  In fact the beds are virtually horizontal, and some of them have a very slight dip northwards, from the valley side out into the valley floor.  This is an important point for the interpretation of the sequence.  

My own detailed section for the site is very long and thin, and is difficult to reproduce  --  but here it is:

Click to enlarge.  The locations of our six exploratory trenches are shown, and it is possible to match at least some of the deposits in the sequence with the Unwin diagrams.  The sands, silts and clays exposed in the southern part of the section (and including organic-rich layers) are highly enigmatic -- are they estuarine, lacustrine, colluvial or fluvial?  

The sharp and unconformable contact between these fine sediments and the more varied reddish deposits with clasts occurs close to point E on my diagram; I studied this closely, and here is my record of what the junction looks like:

Unconformable contact between non-glacial and glacial (?) deposits close to point E in the cliff exposure.  The metre scale on the right shows surveyed altitude above OD.  The displacement of the sedimentary layers is about 1m on slip face (2) and about 30 cms on slip face (3) -- suggestive of fracturing and slippage under permafrost conditions.

 My own observed stratigraphic sequence is this:

10.  Made ground and soil
9.    Dark red stratified horizon
8.    Dark red diamicton (non-stratified)
7.    Orange silt and clay series
6.    Grey silt and clay series
5.    Peat and peaty silt
4.    Stony grey silts -- up to 1.5 m thick
3.    Ferruginous bedded sands and gravels -- up to 1.5 m thick
2.    Rounded pebbles / beach shingle in a sandy and gravelly matrix -- up to 1.8 m thick
1.    Sand layer -- more than 1 m thick

It's difficult to tie in this sequence to that of Dixon (1921) -- although Bowen (1977, Table 3) tried to do just that.  

David Bowen has published extensively on the Pleistocene correlations of South and West Wales, and has referred in a number of publications to the fact that like Dixon he has seen 1.5 m of till at the base of the succession.  He says (1977) that "Dixon's till has been re-exposed and a succession directly comparable to his re-established" -- but no adequate supporting evidence has ever been published, and the bulk of Bowen's mentions of a West Angle till simply consist of references to his own past assertions.   As for the sequence described by myself and David Unwin, a promised "radical revision" written by Ribbon and Bowen has never been published......... so we do not know whether an Irish Sea till has been securely tied in through stratigraphy to the base of the sediment sequence.  I suspect that Bowen's observed till is the same as that which I observed adjacent to cutting B.  I am quite certain that the till which I observed is considerably YOUNGER than the raised beach.

I now think that the band of orange clay shown by Dave Unwin and myself is not a primary sedimentary feature but a weathering or secondary feature. I have learned from looking at scores of other sites in West Wales that horizons such as this exist beneath glacial deposits -- not because these horizons have been exposed to the atmosphere, but because this is where there has been water concentration, leaching and also precipitation of chemicals once held in solution. A virtually identical orange-coloured layer exists beneath the Irish Sea till at Abermawr.  But clearly there has been a "cut" here, with pre-existing sediments eroded away and replaced with later sediments that are themselves slumped or faulted. Are we to interpret these as glacial deposits incorporating overridden sediments and far-travelled erratics laid down in a highly fluid ice-marginal environment? I suggest just that.

The reddish till is seen in the cliff face for about 15m north from point E, unstratified towards its base and stratified above. In a QRA field visit in 1969, some experienced Quaternary experts came to the view that because of the relative lack of large clasts in this material, and the frequency of weathered fragments, it must be a re-deposited ancient till, more properly defined as a slope deposit. This view was repeated by DQ Bowen in a number of papers. However, during one later visit to the site, I was lucky enough to discover, close to cutting B (in the gully down to the beach) an excellent exposure of blue clay till with thrust structures and inclusions of rotted bedrock debris. Adjacent to this was another exposure in which the till had a reddish colour with many ORS fragments included, with clearly striated clasts and with lignite and shell fragments too. This was a classic exposure of Irish Sea till, confirming that the ice of the Devensian Irish Sea Glacier did indeed affect this area.

Deposits from this glacial episode are also seen in the northern coves at West Angle -- including a wedge of in situ reddish till in cove number 3 which is packed with fresh striated cobbles, many derived from the ORS.  The till contains flow structures and fluvioglacial lenses, suggesting sedimentation in an ice-marginal environment.

At this stage we should mention two other publications:  one a chapter by Campbell and Bowen in the GCR volume called "Quaternary of Wales" in 1989, and the other  a short paper by CR Morey published in 1997:
Morey, C.R. 1997. A re-examination of the valley-fill deposits at West Angle Bay, Pembrokeshire. Proceedings of the Ussher Society, 9, 164-167.

Campbell and Bowen do not publish any sections or other diagrams of the stratigraphy, and Morey's illustration of the sequence is so generalised and inaccurate as to be effectively useless.  Morey does not accept that there is a genuine raised beach deposit near the base of the succession at West Angle, and nor does he accept that his "reddish brown" layer 4(i) is a till layer, in spite of recording within it clasts of ORS marls and sandstones, dolerites and rhyolites.  He prefers to follow Bowen (1974) in interpreting this as a periglacial head or slope deposit accumulated under permafrost conditions.  He does not explain where all this erratic material might have come from.  Nor does he seem to have examined the fresh till that is exposed in the northern coves of West Angle Bay; such an examination might well have convinced him that Late Devensian ice did indeed reach this locality and must have affected the sedimentas at the head of the main bay.  Campbell and Bowen accept the presence of the raised beach, and its dating as Ipswichian, but are ambivalent on the matter of the "reddish till".  They do however accept the contention by Bowen that there is indeed an exposure of Irish Sea till BENEATH the raised beach.  No evidence is cited in support of this thesis  -- so the jury is still out on the matter.

In 2000 Kenneth Rijsdijk argued that the whole of the sediment sequence at West Angle is of Devensian age, with different layers representing  differing environmental and climatic episodes. 

So we have -- by less than common consent -- a raised beach that appears to be of Ipswichian or Last Interglacial age, and above it a reddish diamicton (which I consider to be till) that must be related to the Devensian Irish Sea till which is found in many locations around the northern and western coasts of Pembrokeshire.  In between those two recognisable deposits we have a suite of clays, silts, sands and gravels with an incorporated layer of peat and peaty silt.  These deposits occupy an equivalent stratigraphic position to the "lower head" or stratified slope deposits assumed elsewhere to be of Lower and Middle Devensian age.  So what were the climatic and environmental conditions which led to the accumulation of these deposits at West Angle?

There are two big questions:

1.  Are there really two tills of different ages at West Angle?
2.  What is the nature of the layers of sands, silts, and peaty loams between the raised beach cobbles and the reddish till?

To be continued.......

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

Some key references:

BOWEN, D. Q. (1970). South-east and central South Wales. In: The Glaciations of Wales (Ed. by C. A. Lewis). Longmans, London.

BOWEN, D. Q. (1980). The Pleistocene scenario of Palaeolithic Wales. In: Culture and Environment in Palaeolithic Wales (Ed. by J. A. Taylor), pp. 1-14. British Archaeological Report, no. 76.

Dixon, E.E.L.  (1921)

JOHN, B. S. (1968). Age of raised beach deposits of South-western Britain. Nature, 218, 665-667. 

MITCHELL, G . F . (1960). The Pleistocene history of the Irish Sea. Advancement of Science, 68, 313-325.

MOREY, C.R. (1997(. A re-examination of the valley-fill deposits at West Angle Bay, Pembrokeshire. Proceedings of the Ussher Society, 9, 164-167.
http://ussher.org.uk/journal/90s/1997/documents/Morey_1997.pdf

PHILLIPS, L . (1974). Vegetational history of the Ipswichian/Eemian Interglacial in Britain and Continental Europe. New Phytologist, 73, 589-604.

RAWITSCHER, (1945). The hazel period in the post-glacial development of forests. Nature, 156, 302-303.

Stevensen, A.C. and Moore, P.D. (1982). Pollen Analysis of an Interglacial Deposit at West Angle, Dyfed, Wales. The New Phytologist. Vol. 90, No. 2, pp. 327-337.

TURNER, C. (1970). The Middle Pleistocene deposits at Marks Tey, Essex. Philosophical Transactions of the Royal Society of London, B, 257, 373-440.

TURNER, C. & WEST R. G. (1968). The subdivision and zonation of Interglacial periods. Eiszeitalter und Gegenwart, 19, 93-101.

WEST, R . G . (1980). The Pre-glacial Pleistocene of the Norfolk and Suffolk Coasts. Cambridge University Press, Cambridge.

Catling on Neolithic Pembrokeshire

Quite a hefty article from Chris Catling in Current Archaeology for March 2017.  Thanks to Dave and Tony for bringing it to my attention.

It's a strange article -- part review of a chapter in the new Pembrokeshire County History volume, part report on what was said at the latest NPA Archaeology Day, and part opinion piece.  CC follows a line of argument from Tim Darvill -- namely that there has been too much stress in the past on "monument typologies" and not enough on the purposes and intentions on the builders -- in other words, what the monuments meant to the builders.  When  I read that, I thought:  "Here we go again.  Away with hard evidence -- let's have fun with fantasies instead....."

Were my misgivings borne out by what followed in the article?  Well, yes and no.  I liked the points about the diversity of Neolithic monuments, the need to adapt to local materials and locations, and to "show off" to the neighbours.  But I found the arguments about "propped rocks" or sub-Neolithic chambers, a bit strange -- and I'm not sure that it gets us anywhere to imagine that prehistoric men were seeking to imitate nature in their early stone settings -- on the basis that strange rock formations or arrangements might have been created not by nature but by some lost race of giants or gods.  It's just as likely that the Neolithic inhabitants of the Pembrokeshire landscape were perfectly indifferent with regard to rock outcrops, tumbled crags, erratics and scattered stones.  CC says that "many propped rocks occupy impressive settings"  -- you could just as well say, in my experience, that just as many of them do not.  As far as I am concerned, propped slabs occur all over the place, in places where slabs were found.  Perfectly simple.

Were monuments intended to be seen from afar?  This is a much discussed topic, and CC does not add anything new on this.  Were the simplest monuments "statements of occupation"?  Well, of course they were -- nothing very significant about that.  People built things on the land they occupied, then as now.  On dolmens with "lifted capstones" obviously much more labour was involved -- and of course there was more technical skill and more ambition.  Portal dolmens were more complex still.  There are some interesting points about the evolution and re-fashioning of monuments like Pentre Ifan over time, but the author seems uncertain whether the Pembrokeshire monuments arose out of a multitude of contacts with other parts of the Neolithic world, or whether (as TD seems to be arguing) each one is essentially unique.

Were the monuments set into sacred and secular zones, as Prof MPP has argued?  In partial answer to that, CC argues that some megalithic monuments in Pembrokeshire are set into the landscape "as counterpoints to natural features".  He cites Garn Turne and Carn Bica  as being counterpoints, where natural features have been enhanced and modified.  I disagree completely with this fanciful search for significance -- you could just as well use similar language for any construction in any landscape.  Portal tombs, he says, look out over sea and mountain.  Of course they do -- where else are they supposed to look?

CC repeats the hoary old myth (invented by Darvill and Wainwright) that there is a strong association between megaliths and springs in Pembrokeshire and that this is the basis of the "healing bluestones" fantasy.  There is no such association, and I wish people would stop repeating it uncritically.

CC then comes on to the Neolithic preference for particular rock types, and claims that there was an "astonishing" knowledge of geology, with Neolithic geologists travelling vast distances to source preferred stones.  But he does not adequately differentiate between tool manufacture and megalith building.  As far as I can see, in Pembrokeshire there has been NO preferential use of specific rocks in any of the types of dolmens found in the landscape.  Always, people used whatever was to hand in the vicinity.  That point has been made by many experienced archaeologists.

CC concludes "Rock in prehistory was something living and resonant with meaning", and argues that instead of collecting hard evidence and working on "typology" archaeologists should become more concerned with meanings and the search for significance.  Hmmm -- from where I stand, there is too much fantasy as it is, and we hardly need more of it.   This article really adds very little to what we knew already, but the illustrations are pleasant enough. 

Case dismissed for lack of evidence.

Devensian till at the Blue Lagoon, Abereiddi

One does not often see exposures of Devensian till on the north Pembrokeshire coast, except in valleys and bays where till is often found as a "plug".  However, there is a splendid exposure at Abereiddi, near the famous flooded quarry called the Blue Lagoon.  Above are a couple of photos.

As we can see, the clifftop till is here about 3m thick, resting on broken shale bedrock.  The till is full of rounded, striated and faceted cobbles and erratics.  The matrix is clay-rich, but more gravelly in patches.  There is some iron-staining, but by and large the larger stones are fresh in appearance, just as they are in all of the other Devensian till exposures in North Pembrokeshire.

I'm not making any particularly new point here.  This is just for the record.......

Llansteffan and the Altar Stone

Thanks to Geraint Owen for further information on the Senni Beds.  He has studied the Craig Ddu section in detail, and from his descriptions, and the work of  Ixer, Bevins and Turner, I am now more than ever convinced that the Altar Stone might well have come from Craig Ddu near Llansteffan. Below I reproduce some of the key info on the Senni Beds from the big report by Barclay et al 2015.
 It's clear from the published work that the Altar Stone has significant differences from the Cosheston Sandstones around Mill Bay (Milford Haven) and significant similarities with the sandstones described from Craig Ddu.  The samples are not identical, but that is not surprising;  we do not know the precise positions from which all the samples have been taken, along a rock exposure c 400m long and 20m high.

For the moment, until further work is done, I think we can assume that the Altar Stone has probably come from the Llansteffan Peninsula and maybe even from the Craig Ddu exposures. That makes perfect sense, since the eastern Preseli hills and the Llansteffan Peninsula are on pretty well the same Irish Sea Glacier flowline.  All of the speculation about the Altar Stone having come from somewhere along the A40 road between Llandeilo and Sennybridge becomes redundant.

  

Flow lines and erratic trails -- reconstruction by Olwen Williams-Thorpe, after Kellaway.  Note that the pinkish coloured flowline crosses both Preseli and the Llansteffan Peninsula.

 ==========================

Big BGS report on ORS stratigraphy.  It provides a more formal correlation of Cosheston Group and Senni Formation:

BARCLAY, W J, DAVIES, J R, HILLIER, R D, AND WATERS, R A. 2015. Lithostratigraphy of the Old Red Sandstone successions of the Anglo-Welsh Basin. British Geological Survey Research Report, RR/14/02. 96pp.
It's a free download from the BGS website.

Extract:

4.2.5     Senni Formation

Name
Derived from the Senni Valley (Glyn Senni), Powys, south-central Wales. The name Senni Formation supersedes the traditional Geological Survey name Senni Beds (Cantrill in Strahan et al., 1904). In the Clee Hills, the formation was previously named the Clee Sandstone Formation.

Type area
Senni Valley [SN 930 209]

Partial type section
Waterfall exposures [SN 930 209] in a tributary of the Afon Senni (Nant Ystwyth) above Tyleglas.

Reference sections

1.    Heol Senni Quarry [SN 9154 2210], Powys provides a well documented reference section. It exposes about 40 m of grey-green sandstones, with minor siltstones, mudstones and intraformational conglomerates at the top of the formation (e.g. Edwards et al., 1978; Loeffler and Thomas, 1980; Dineley, 1999b; Barclay, 2005e).

2.    Cliffs at Craig Ddu on the western side of the Llansteffan peninsula, Carmarthenshire [SN 32441015](Owen, 1995). These reach a height of 20 m and have continuous exposure for 400 m of beds near the top of the formation.

3.    The stream draining north-westwards across Clee Liberty [SO 583 848–587 844] in the Clee Hills exposes about 140m of the formation (Allen, 1961) and provides a reference section for this area.

Lithology
Mainly of green and green-grey (locally red-brown and purplish green), very fine to medium- grained, micaceous sandstones, mainly channelised, cross-bedded and parallel-laminated, with green and red-brown siltstone and mudstone interbeds, some calcretes and intraformational conglomerates; the formation is characterised by the presence of vascular fossil plant remains and some soft sediment deformation is also present. In the Clee Hills, pale green sandstones are mainly arranged in fining-upwards conglomerate–sandstone–siltstone cycles, with subordinate red or green, sporadically calcretised mudstone/siltstone interbeds (Ball and Dineley, 1952, 1961; Allen, 1961; Greig et al., 1968).

Lower and upper boundaries
The lower boundary is placed at the base of green sandstones, which overlie red-brown sandstones and mudstones of the underlying Freshwater West (formerly St Maughans) Formation. Where mature calcretes at the top of the Freshwater West Formation are present (the Ffynnon/Abdon Limestones), the base of the formation is placed at the top of the uppermost calcrete. The upper boundary is placed where red-brown sandstones of the Brownstones Formation overlie the green sandstones of the Senni Formation, the junction being gradational. In the Clee Hills, Here, the lower boundary of the formation is placed at an erosion surface cut in the uppermost calcrete of the Upper Abdon Limestone, where it is sharply overlain by the basal green sandstones. The upper boundary is a gradational passage into generally coarser-grained
strata lacking in argillaceous beds and in which the sandstones are more variably coloured, these being assigned to the Brownstones (previously Monkeys Fold) Formation.

Thickness
300 to 450 m in the Brecon Beacons and Black Mountain, 150 to 200 m in the Black Mountains and 152 to 167 m in the Clee Hills.

Distribution
From Carmarthen Bay eastwards to the Black Mountain, Brecon Beacons and Black Mountains, and from there southwards to Abergavenny, wedging out north of Pontypool.

Depositional environment
High-discharge, mixed-bedload, sand-dominated, braided stream systems with relatively high sedimentation rates and water-table levels; although the formation is dominated by in-channel deposits, overbank floodplain silt and mud deposition also occurred.

Age
Latest Lochkovian to latest Pragian or Emsian in age.

REFERENCES

OWEN, G. 1995. Senni Beds of the Devonian Old Red Sandstone, Dyfed, Wales: anatomy of a semi-arid floodplain. Sedimentary Geology, Vol. 95, 221–235.

see also:

Also, RG Thomas's opus magnus on the Cosheston Group, which includes petrographic data:
THOMAS, R G, BARCLAY, W J, MORRISSEY, L, WILLIAMS, B P J, and ALLEN, K C. 2006. Enigma variations: the stratigraphy, provenance, palaeoseismicity and depositional history of the Lower Old Red Sandstone Cosheston Group, south-central Pembrokeshire, Wales. Geological Journal, Vol. 41, 481-536.

Rhosyfelin -- Coflein record is corrected

After lots of messages and a good deal of confusion, this is probably as right as it ever will be   -- it should now be almost acceptable to both sides of the argument!! 

I suggested further corrections, but these have been ignored.......


http://www.coflein.gov.uk/en/site/416247/details/craig-rhosyfelin-pont-saeson-craig-rhos-y-felin-rhyolite-bluestone-outcrop

Site Description

Fieldwork in 2011-12 led to the proposal that most of the foliated Stonehenge rhyolite debitage originated from a specific 70m long area called Craig Rhos-y-felin near Pont Saeson. Petrographical sampling by Dr Rob Ixer and Dr Richard Bevins found that 99% of these foliated rhyolites could be matched to rocks found in this particular set of outcrops. Rhyolitic rocks at Rhos-y-felin are distinctly different from all others in South Wales, which suggests that almost all of Stonehenge foliated rhyolites have a provenance of just hundreds of square metres. The results were of considerable significance, and were published in 2011 in the Journal of Archaeological Science.

Excavations between 2011 and 2015 identified Neolithic activity that may have been associated with megalith quarrying, but this is disputed by geologists, who believe that erratic materials were entrained at Rhosyfelin by over-riding glacier ice and transported south-eastwards towards Stonehenge.

Sources:

Bevins, R.E., Pearce, N.J.R., and Ixer, R.A., 2011, Stonehenge Rhyolitic bluestone sources and the application of zircon chemistry as a new tool for provenancing rhyolitic litics. Journal of Archaeological Sciences, 38, 605-622.

Ixer, R.A., Bevins, R.E., 2011, Chips off the Old Block: The Stonehenge Debitage Dilemma. Archaeology in Wales, 52, 2011, 11-22.

Brian John, Dyfed Elis-Gruffydd, and John Downes, 2015, Quaternary Events at Craig Rhosfelin, Pembrokeshire. Quaternary Newsletter 137, October 2015, p16-32.

Mike Parker Pearson, Richard Bevins, Rob Ixer, Joshua Pollard, Colin Richards, Kate Welham, Ben Chan, Kevan Edinborough, Derek Hamilton, Richard Macphail, Duncan Schlee, Jean-Luc Schwenninger, Ellen Simmons and Martin Smith (2015). Craig Rhos-y-felin: a Welsh bluestone megalith quarry for Stonehenge. Antiquity, 89 (348) (Dec 2015), pp 1331-1352.

L. Osborne & T. Driver, RCAHMW

Here comes Super-Stonehenge........

Talking of hokum, as we do quite often on this blog, wait for it....... here comes the latest blockbuster for Sky TV.  It's called "Britannia".  It will be broadcast this year, and featuring large will be a sort of Super-Stonehenge around which the drama involving Druids, Celts and Romans will swirl, no doubt with plenty of magic, monsters, and blood and gore.  Historical accuracy cannot be guaranteed.......

For those who like this sort of thing, here is the key info, put out by the publicity people:

Full credits for Britannia -- 10 episodes coming up in 2017

http://www.imdb.com/title/tt5932548/fullcredits?ref_=tt_ov_st_sm

Britannia is an epic drama set in 43AD as the Roman Imperial Army - determined and terrified in equal measure - returns to crush the Celtic heart of Britannia - a mysterious land ruled by warrior women and powerful druids who can channel the powerful forces of the underworld. Or so they say.

http://www.radiotimes.com/news/2016-12-07/first-look-at-david-morrissey-and-kelly-reilly-in-epic-new-historical-drama-britannia

Sky and Amazon partnership  -- filming in Czech Republic and Wales 2016.

The international distribution rights (excluding the US) for Britannia will be handled by Sky Vision, Sky’s international production and distribution arm. WME and Sky Vision negotiated the deal with Amazon.

Commenting on the show, Jez Butterworth said: “Besides being hard, hard warriors, the Celts have a belief system which makes them almost invincible. It’s a deep, heavy magic. Last time the Romans tried to invade, the mighty Julius Caesar took one look, turned round and went straight home. Now, almost a century later, the Romans are back. I’m fascinated in what happens when gods die. When an entire, ancient faith stalls, topples, collapses - and a whole new one grows in its place. New names, new faces, to suit the new times. Here we have a  war between two pantheons - the Roman gods v the Celtic gods. It’s the Heavyweight Clash of All Time, the one which most shapes who we are today. And we see it all from a human perspective, of individual survival, ambition, courage, lust, loss, revenge. All the stuff the gods have always loved us humans for the most!”

Kelly Reilly said: "I am thrilled to be joining the production of Britannia, a story rooted in the heart of our ancient history. Collaborating with great creative minds is what I love most about my job, and having one of Britain’s leading playwrights, Jez Butterworth, come on board to bring Celtic Britain alive has made this a fiercely exciting project. The vision is big and bold and beautiful, and I can’t wait to get my hands dirty.”

David Morrissey added: "I have been a fan of Jez's writing for a long, long time, so to get the chance to work with him on this epic tale is very exciting. His dialogue and storytelling are second to none. I am also really looking forward to working with the brilliant cast that has been assembled for Britannia - I just hope I get a nice horse!"

Anne Mensah, Sky’s Head of Drama said: “This is one of the most ambitious dramas we’ve ever made and one of the most exciting. Jez Butterworth has written an incredible drama that is entertaining and emotional but also asks important questions about what drives men and women to stand and fight. This is a battle for the heart of Britain like you’ve never seen before.”

Roy Price, Vice President, Digital Video and Amazon Studios, said: “We’re thrilled to be collaborating with Sky on our first series entirely produced overseas. Our customers will experience a cinematic world with bold characters anchored in a ruthless period of history.”