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

Thursday, 30 October 2014

EH makes monographs available for free


 Good for EH -- they have just made a long list of research monographs available for free download.  Some very interesting materials is included in the list........


http://archaeologydataservice.ac.uk/archives/view/eh_monographs_2014/index.cfm?type=Date

Abermawr -- one of the top 50 Quaternary sites in the UK?



 The deformed contact between underlying periglacial slope deposits of Early / Middle Devensian age, and the overlying Irish Sea till, laid down by Late Devensian ice moving onshore from the north-west

The QRA (Quaternary Research Association) is asking all its members for nominations for the "top 50" Quaternary sites in the UK.  I have nominated Abermawr -- it has to be up there with the best!


Here is my citation:
This is the most comprehensive exposure of Late Pleistocene deposits in West Wales.  There are exposures at both ends of the bay.  Storms have revealed an Ipswichian raised beach on a rock platform remnant, and above that there is a sequence of periglacial deposits made up of angular bedrock fragments, but incorporating far-travelled erratics.  Above that is a clay-rich Irish Sea till of Late Devensian age and containing striated clasts, fragments of carbonized wood and sea shells.  The main components of the till are sea-floor deposits, dredged up by glacier ice moving across the old coastline and later laid down by lodgement and shearing.  There are also flow-tills, and the glacial deposits are capped by fluvio-glacial materials, an upper head (referred to in the past as “rubble-drift”), sandy loam and modern soil.  The deposits represent a complete advance/retreat cycle close to a glacier margin. In the upper head there are fossil ice-wedges and involutions of Late Glacial age.  Beneath the storm beach there are peat beds and remnants of the “submerged forest”, and these organic-rich sediments can be examined in the marsh on the landward side of the storm ridge. There is a continuous stratigraphic record here, probably stretching back c 100,000 years.

Rijsdijk, K and McCarroll, D. 2001. Abermawr, in The Quaternary of West Wales Field Guide, QRA, pp 32 - 38.

John, BS 1970. Pembrokeshire, in  Lewis, CA (ed) The Glaciations of Wales and Adjoining Regions, pp 229-265

Wednesday, 29 October 2014

Was Cardiff Bay affected by Devensian ice?


With reference to my earlier post about the position of the Devensian ice front on the southern flank of the Welsh Ice Cap, there is still disagreement among geomorphologists.

This section of the BRITICE Devensian map shows abundant glacial / fluvioglacial deposits in the Cardiff - Newport area, but the compilers of the map decided that the Vale of Glamorgan was ice-free at this time, as was the coastal stretch to the east of Lavernock point.  The dotted line on the map shows the assumed maximum ice front position.

In contrast, Devensian ice lobes are assumed to have reached the Bristol Channel lowlands (ie beyond the present coastline) both in Swansea Bay and Carmarthen Bay.

My earlier post is here:
http://brian-mountainman.blogspot.co.uk/2014/10/flat-holm-erratic-hunt-6-lets-imagine.html

The extensive spreads of ice-related deposits shown on the map were assumed by Charlesworth in 1929 to represent the position of the South wales End Moraine, but it's now known that things were much more complicated than that.  Some of the deposits on the map are Devensian, and some may well be much older.......  In some of the reconstructions by Prof DQ Bowen over the years, he has an ice lobe pushing offshore between Cardiff and Newport, and in others the lobe fails to reach the coast.  Work in progress?

Saturday, 25 October 2014

Mystery

Just been alerted to the fact that 1470 people have looked at this blog post about braided rivers in Iceland......
http://brian-mountainman.blogspot.co.uk/2014/05/braided-rivers-in-iceland.html

Well over 700 have looked at it today -- I wonder why?  Does anybody else have any idea what's going on?  Admittedly, they are very beautiful images......

Tim's Long Barrow opens for business


Tim's long barrow is open for business -- and if you want to take a look, get over there right now!!  More info here on the BBC web site:


 and here, on Tim's site:




Wednesday, 22 October 2014

BRITICE map of Pembrokeshire's old glacial deposits


This is the relevant piece of the BRITICE map of glacial deposits and other features relating to the Last Glaciation.  It's a few years old now, and new information has made parts of it look dated, but it was the state of the art summary when it was published, and it's still a valuable aid to future research.  The whole map is in two sections available for download -- northern and southern sheets.  This extract is from the southern sheet.

The map shows the area assumed to have been ice-free in the Devensian (faint yellow colouring), main spreads of fluvio-glacial gravels (brown), proglacial lakes (blue), meltwater channels (dark blue), glacial limits (dotted lines) and assumed ice dam positions (yellow lines).

Let's forget about the north Pembrokeshire features for the moment and concentrate on those of central Pembrokeshire.  The patches of glacial deposits (gravels and till) shown are generalised from the BGS Geology of Britain map at the 1:50,000 scale.  Those of the Western Cleddau valley are well shown, as are the sand and gravel patches to the east of Haverfordwest, in the Clarbeston Road - Clynderwen area.  But the patches to the north, in the foothills of Preseli, are not shown, probably because they are not extensive enough.  But they are rather intriguing, as I suggested yesterday.  What do they tell us about the glacial history of West Wales?  I'm on the case......

http://mapapps.bgs.ac.uk/geologyofbritain/home.html

http://www.britice-chrono.group.shef.ac.uk/current-sampling-map/

http://www.sheffield.ac.uk/polopoly_fs/1.22760!/file/britice_2004_s.pdf

Tuesday, 21 October 2014

Pre-Devensian glacial deposits south of Preseli


Fluvio-glacial sands and gravels (shown in pink) in the area around Llangolman and Maenclochog, to the south of the Preseli upland.

 Some more original field research here, for those who may be interested.......

Thanks to Huw Absalom of Bush Farm, Llangolman for the opportunity to look at his splendid gravels today.  Very interesting indeed.  I have been frustrated for some time because although there are plenty of patches of glacial and fluvio-glacial deposits in the central and southern parts of Pembrokeshire, as shown on the geological maps, they are very seldom exposed for proper examination.  They should be pre-Devensian if we have got our ice limits in the right places -- but hard evidence of great age was required.  

So when I got a message from Sid Howells telling me that Huw wanted somebody to take a look at the gravels in his small pit close to the Church of St Colman, I got onto the phone and organized a visit.  So I have been over there today, and things are starting to look good.

The pit (grid ref SN 115268) is not a commercial one -- it's just used for providing hardcore and concrete ballast for use on the farm.  It's about 30m across and 10m deep, exposing fluvio-glacial gravels and sands in the full height of the face.  It's cut into the top of an undulating terrace which has clearly undergone a long history of erosion, especially on its northern flank, where the slope drops down into a small tributary valley which is part of the Eastern Cleddau river system.  The valley is about 25m deep.  Huw tells me that clay is exposed on the floor of the valley, and that there are also exposures of sand not far from the stream.  It's a reasonable assumption that clay-rich till underlies the sands and gravels.

The exposed gravels are relatively  fine-grained, with no cobble-sized beds or boulder beds -- indicating turbulent but not violent torrential flow.  There are a few interbedded sand horizons, suggesting periods of quieter flow.  The bedding dips quite steeply from NW towards SE -- so this may indicate the presence of an advancing delta front close to an ice edge.  This is supported by the presence of some larger stones in the gravels, up to football size, and quite angular.  There is one large chunk of bluish rhyolite which looks as if it has come from a larger boulder.  I didn't see any striated pebbles, but I would not be surprised if some were to turn up......  But the gravels are packed with erratics, including assorted Fishguard Volcanics, rhyolite, dolerite and one quite distinctive pebble of Carboniferous Limestone.  (Where on earth did THAT come from?)

Typical gravels exposed in the Llangolman quarry face.  Note the overall alignment of long axes from top left to bottom right.  Note also just how many pebbles are heavily weathered if not rotten.

One of the black layers cemented with manganese oxide, above a sand bed about 20 cms thick.  


Fragments of the lowest black "manganese concrete" layers in the quarry, which was so hard that it had to be broken up with a tractor grab.  Note also traces of foxy-red "iron oxide" concrete.

I have never seen so many layers of manganese concrete in a single small quarry face.  There are at least six of them, including one just a metre or so beneath the ground surface.  This fact, together with the extremely rotten character of many of the pebbles in the gravels, is suggestive of great age.  Maybe we are looking at deposits from the Anglian glacial episode of about 450,000 years ago.

Great age is also indicated by the presence of "churned gravels" near the ground surface which have lost all trace of their original bedding, and several distinct fossil ice wedges and frost fissures within which many of the pebbes are "standing" with their long axes vertical.  That is indicative of pebbles falling or sliding down into an open frost track or wedge from which the ground ice has temporarily melted.  The assumption?  Thick and long-lived permafrost -- maybe for many thousands of years.



The two photos above have been annotated to show the outlines of the ice wedge casts.  Each one is between 2m and 3m deep.  Note how the gravels and sands are "churned" within the casts and normally bedded on the flanks.  I have also annotated the surface layer of gravels, where signs of frost heave are abundant.  This layer is sometimes just 50 cms deep, and in other places well over 1m deep.

Next time I visit the pit, Huw has kindly offered to be in attendance with his digger -- so we can go down deeper, and maybe find some till........

And speaking of till, it is exposed on the flank of a small stone quarry at Plascwrt, at SN 118274.  It's clay rich, with smallish pebbles and cobbles some of which are well rounded far-travelled erratics.  It is friable to the touch, and foxy red in colour.  So again the impression is that it is severely weathered as a result of many thousands of years of exposure to weather of many types.....


The reddish till layer above fractured bedrock in the small stone quarry at Plascwrt.  It is clay-rich and contains abundant erratic pebbles.


Tentative conclusion: these are very old glacial deposits which display a quite different combination of features from those exposed on the northern side of Preseli, which are deemed to be of Devensian age.  My guess is that these are of Anglian age -- or maybe Wolstonian.  (That's a glacial episode that we know very little about, at least in Western Britain.)





Rhosyfelin -- the scheduling issue




I think I have got to the bottom of the mystery about the request to Cadw for the designation of Rhosyfelin as a Scheduled Ancient Monument.  I have received a couple of very helpful letters from Cadw, and it seems that something like this has happened. 

Somebody (we don't know who) asked the Director of Cadw and the Head of Historic Environment to visit the dig site and take a look at it -- which they did, presumably during the September dig. 

Subsequently the Cadw archaeological inspectorate was asked to give a considered view on whether the site met the criteria for ancient monument scheduling.  Presumably they must have visited as well.  However, says the letter, "we were unable to do so (ie advise positively) in the absence of archaeological reports or other supporting evidence.  The site therefore remains on our radar for consideration."

The letter also says that no formal request has been received from any external party for scheduling -- and we must accept that statement in good faith.

There are still some interesting questions that might be asked about the timescale and the sequence of events, and I still suspect some "informal involvement" from the National Park.  But I'll now let this matter rest, content in the knowledge that there is no great conspiracy going on, and that Cadw will not do anything precipitate.  What everybody (including Cadw) now wants, it seems, is some written reporting and some hard evidence.......

So thanks are due to Cadw for keeping us in the picture on this.

 

Geology of Britain Viewer -- Craig Rhosyfelin



I'm more and more impressed with the BGS Geology of Britain Viewer:

http://mapapps.bgs.ac.uk/geologyofbritain/home.html

which you can use to zoom in on anywhere in the country so as to pick up on the details of solid or superficial geology or a combination or the two.  The best scale to look at is 1:50,000, since on smaller scales there are some rather strange amalgamations of categories which might leave you confused.  Indeed, some of the classifications are confusing anyway -- but that's not surprising, given the difficulty of classifying either sold rocks of or superficial materials when you are wandering around in the field.

If we look at the screenshot above, we can see the vast spread of till in the lowland between the Preseli ridge and the Brynberian - Crosswell area, confirming my suspicions that the Devensian Irish Sea Glacier did push across this area.  I think the BGS surveyors have got things pretty well right.

And look at the Craig Rhosyfelin area -- we should not be at all surprised to see, exactly at the site of the archaeological dig, a series of different deposits including till, rockfall materials, torrential fluvioglacial materials, and alluvial and colluvial deposits incorporating frost-shattered slope detritus.  Exactly as I have described them.......

By the way, on the map the pink areas are spreads of fluvio-glacial materials.  The light brown areas with relief shading on them show territory where there are no thick sediments but thinnish soils resting directly on bedrock.

Monday, 20 October 2014

Arwel Afanc and the Quarry of Gloom


 Perhaps the "proto-orthostat" at Rhosyfelin was a ping-pong table?  Looks remarkably like it.  But I digress.......


Mindful of the recent learned discussions on this site, I have started work on the latest blockbuster series for the small or large screen.     I am also mindful of the fact that Tony is pitching to be executive producer of the series, or at the very least,  casting director.   That's fine by me -- he clearly has what it takes.

Like all the best blockbuster sagas, the whole thing has to be based on the truth, with a modicum of fantasy added to keep the youngsters happy.  Arwel Afanc is a name that rolls off the tongue nicely, and it has a subtle ethnic ring to it.  There are also resonances with Buffalo Bill, Crocodile Dundee, Tiger Woods, Nigel Molesworth and other heroic figures from the past who are linked with the names of fierce creatures..........

As ever, I am starting from the end and am working towards the beginning.  The conclusion has to be the discovery of a body crushed beneath that gigantic proto-orthostat which was about to be shipped off to Eric the Red in southern Greenland when everything suddenly went wrong.  Whose body was it?  Watch this space......

Saturday, 18 October 2014

More about the Afanc


I had omitted to mention, for those who might not know what an Afanc looks like, that a very nasty one appeared in that well-known historical BBC TV documentary series called "Merlin."  This one was created by magic in very dodgy circumstances, and appears to have caused a spot of bother to those great buddies Arthur and Merlin.

Best to leave him undisturbed, if possible, down there in his watery cavern......

Sorry if this upsets those of a sensitive disposition -- but the truth must be told.

The Brynberian Afanc


The fair maid of Brynberian, who allowed herself to be used as bait for the fearsome water monster called the Afanc....

Thinking about myths and legends, as one does from time to time, I recalled that the Afon Brynberian, which flows past Rhosyfelin, rises on the moorland on the northern slopes of Preseli.  There's an ancient tale centred on Bedd yr Afanc and Brynberian Bridge, less than 2 km upstream of Craig Rhosyfelin.  I published this tale in my book of folk tales called THE LAST DRAGON, in 1992.  Here it is again -- make of it what you will.......

(I have told this tale before on this blog, in two different forms, but it seems timely to tell it yet again, since such tales are now being hijacked and converted into official history!)

4.6 The Brynberian Afanc

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, and is 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 bated 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 master 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.

Date: c 1300? Sources: Rhys p 689, Davies p 325

Wednesday, 15 October 2014

Glaciation of Rhosyfelin

I was down at Rhosyfelin this morning with geologist John Downes  -- of which more in due course.
But on the matter of glaciation, the signs are more and more obvious.

I got a better photo of the beautiful ice-moulded surface close to the tip of the spur:


I'm not sure how the archaeologists explain away features like this.  Maybe they had apprentice quarrymen in the bad old days, who were given menial tasks like polishing and smoothing rock outcrops, so that they would be really good at it by the time they got to Stonehenge?  The trouble is that there are smoothed and worn surfaces like this all over the place, and many of the bedrock outcrops in the vicinity of the wonderfully-named "proto-orthostat" are equally well worn.  My guess is that the features have been shaped both by glacier ice and by torrential meltwater during deglaciation.

I'm more and more convinced that the abundant rounded and sub-rounded erratics in the till and the fluvio-glacial deposits have come from the west and north-west, where there are many outcrops of dolerite and other volcanic rocks belonging to the Fishguard Volcanic Series.  The upstanding tors of Carnedd Meibion Owen are only about 3 km away,  and there are more dolerites exposed near Pentre Ifan, about 4 km away to the NW.  That would match up with the suggested direction of Devensian ice movement very well.  Next time I go down I hope I'll also have a geologist with me, so that we can look seriously at the likely provenances for the dolerites and also for rocks like this erratic cobble about 6" long:



The lower picture shows a fragment from the same stone, about 2" long.  I think it's an ash or tuff from the Fishguard Volcanics, but I can't be sure until somebody more expert looks at it.  It's  not from Rhosyfelin, I reckon. 

I'm also coming to the view that the grey clay-rich deposit art the base of the sequence on the valley floor MAY be a deposit from a short-lived proglacial lake.  Watch this space.

Another thing I've been pondering on is the orientation of the meltwater channels at Rhosyfelin.  The little one runs NNE, and the big one runs NNE and then swings towards the NW -- and this latter orientation runs directly counter to the direction of Devensian ice flow around 24,000 - 20,000 years ago.  The channels themselves are much older -- I suspect that they date from the Anglian.   The fluvio-glacial materials in the valley are suggestive a powerful meltwater flow -- probably unconstrained by any ice barrier.  So that means the valley carried a large stream at quite a late stage of deglaciation.  This brings up another interesting question -- could the meltwater have come from the melting of a late Preseli ice cap which remained in existence after the dissolution of the Irish sea ice in the area?  That's an intriguing thought.......













Scheduled Ancient Monument status for Rhosyfelin? Somebody must be joking....


 
 The scheduling of Ancient Monuments in Wales.  In the case of Harlech Castle, nice and easy........

... and in the case of Rhosyfelin, fascinating geology and geomorphology, and not a lot else.


A few weeks ago I learned that somebody (still not sure who) has submitted a request to Cadw for Craig Rhosyfelin to be given Scheduled Ancient Monument status.  I almost fell off my chair when I heard that, since the request must be based on the fact that this is a "Neolithic Quarry" and since not a scrap of evidence has ever been seen by anybody which supports that designation.

So behind the scenes I have pleaded with the National Park, Dyfed Archaeological Trust, Cadw and the Royal Commission on the Ancient and Historic Monuments of Wales (RCAHMW) to reject that application out of hand, so as to avoid the possibility that a lot of people will end up looking very stupid indeed.  At last I have received an assurance from a senior staff member at Cadw that nothing precipitate will be done, and that "we only recommend sites for protection when we are satisfied that they meet the criteria for scheduling as a monument of national importance."

She continued:  "In carrying  out a scheduling evaluation we take account of all available information including excavation and other reports, undertake our own site inspection to confirm that the remains meet with our expectations and consult with relevant specialists including the Welsh Archaeological Trusts and Royal Commission on the Ancient and Historic Monuments of Wales, as appropriate. In addition, we have internal processes to ensure that all recommendations are seen by a Senior Inspector of Archaeology."

So there is some reassurance there, and while the application for scheduling has not been thrown out there seems to be an awareness that extreme care needs to be taken in this case.  We shall see how things evolve.  What I am still unsure about is the height of the bar when it comes to evidence.  How strong and how well verified does that evidence need to be, and what is required in the way of peer-reviewed or independently assessed reporting?  And are the experts involved in the assessment process capable of separating out assertions and speculations from incontrovertible data collected in the field?  Of course, we have to assume that they are.......

Here are the key points which I brought to the attention of Cadw:

1.  There is not a single article in the peer-reviewed literature which presents objectively the "evidence" upon which the quarry hypothesis is based.

2.  The only references I have been able to find are in Parker Pearson's Stonehenge book (2012) which was of course not peer reviewed, and assorted talks and popular articles designed for public consumption.  They are full of assertions and speculations, and are significantly lacking in hard evidence.

3.  There have been no internal progress reports or summaries of the dig findings for each excavation season circulated to project partners or to other interested parties.  That may or may not be acceptable to funding organizations -- but it does mean that there is currently no way of assessing how reliable the project's "ruling hypothesis" may be.

4.  In spite of many samples being taken away for analysis, and many being submitted for radiocarbon dating, no C14 dates have been published, and no sample results have been placed in the public domain.  Even the project partners are in the dark as to what is going on.

5.  I think I am right in saying that not a single professional geomorphologist has been invited by Prof Parker Pearson and his team to look at the site, analyse the sediments or comment on the nature of the materials exposed during the digging process.  That is a great pity, since I assume that there has not been a single "restraining" voice in the discussions between archaeologists at the dig -- who do of course have a tendency to see entirely natural phenomena as being man-made.

6.  I have made many visits to the site, and I have not yet seen ANYTHING which convinces me of human intervention at Rhosyfelin, apart, maybe, from a small hearth which might have been used over a long period of time by camping / hunting parties.

Rhosyfelin access




Thanks to the National Park staff and the site owners, we now have the all-clear for earth scientists to take a look at the site where all the digging has been going on.  When I spoke to the owners of the land, they of course pointed out that there is a public right of way adjacent to the large hole in the ground, but it's good to know that they have no objection to bona fide researchers looking at the WHOLE site with a view to moving mankind towards eventual enlightenment........

They didn't even want to be warned in advance of any visits people would like to make -- so that's very kind of them.

In spite of asking the NPA, I am still unclear as to whether another right of way exists to the right-hand side of the crag as seen in the above photo.

Tuesday, 7 October 2014

Preoccupied with East Greenland


Ice, water, land and sky -- two of my favourite images from East Greenland -- both pictures taken near the Bear Islands, in freak light conditions.  Not by me, I hasten to add.......

A bit preoccupied at the moment with getting my new novel into print.  It's called "Acts of God" and is based -- very loosely indeed -- on my experiences in East Greenland in 1962.

It should be out, both in paperback and in Kindle edition, in early November.

So there isn't much time at the moment for thinking about Stonehenge and other frivolous things.






Monday, 6 October 2014

Fracture Plane, Fair Isle, Shetland



In view of our discussions on fracture planes, joints, faults etc, I couldn't resist posting this wonderful photo from Sylvie de Weze -- taken on Fair Isle.  It shows an amazing fault plane which has been exposed by the removal of shattered debris by wave action on either side of a headland.  It's on Fair Isle, south of Shetland -- and the faults seen here (there are lots of them, all more or less parallel) are probably part of the Walls Boundary transcurrent fault system which runs for many miles and which has a displacement along it of as much as 60 km.  The displacement is so great that on Shetland it is impossible to correlate the rocks on either side of the main fault line.

Is Steep Holm a roche moutonnee too?




Phil raises the interesting question as to whether Steep Holm is also a roche moutonnee.  It's a much steeper island, but it is elongated in the direction of ice flow (W-E) and has much steeper cliffs at its eastern end than at its western end.  The island is made of Carboniferous Limestone strata, like Flat Holm -- and because the rocks are dipping westwards there is also a strong structural control here.

The interesting thing about Steep Holm is that it is linked to Brean Down near Weston-super-Mare -- and on that particular piece of the mainland there is a Pleistocene stratigraphy that is quite well known.


Saturday, 4 October 2014

Photo added

A new photo has been added to the last post.  This is a Newport erratic -- I wonder if it comes from the same source area as the Abermawr erratic?  Looks suspiciously similar.












Another mystery erratic from Abermawr




Another erratic which has dropped out of the Irish Sea till at Abermawr.  It's obviously very ancient and has a heavily weathered surface, but the striking thing about it is the presence of these large pinkish crystal agglomerations which are slightly reminiscent of the spotted dolerotes at Carn Meini and Carn Goedog.  The surface of the stone is pinkish brown, but when it is broken open the interior is seen to be very hard crystalline blue-grey.

Anybody prepared to hazard a guess as to where it might have come from?

POSTSCRIPT

 Looking through some old photos, I also found this -- an erratic found on Newport beach, in an exposure beneath the sand dunes.  Could it be from the same place?


Post-Postscript

Now we have another suggestion from one of our blogging community that maybe this is a porphyry.  Here is the idiot's guide to volcanic / igneous rocks:

http://www.nwnature.net/cam/science/rocks/web_rocks/

and this is what porphyry looks like. 


Well, not identical, but maybe in the right general area.  And there happens to be a source of porphyry on Lambay Island off the Irish coast near Dublin. I haven't been able to find a good photo of what this particular porphyry looks like, but it would of course make perfect sense for erratics from Lambay to be incorporated into the Irish Sea Glacier, transported southwards, and then dumped in glacial deposits on the North Pembrokeshire coast.







Friday, 3 October 2014

Fracture Plane -- Abermawr


Following last winter's storms and a series of rockfalls, a beautiful long, straight, flat fracture plane has been exposed at the southern end of Abermawr Bay in North Pembrokeshire.  It compares very nicely with the one at Rhosyfelin..........

Here the rock is thin-bedded Ordovician shales and sandstones.  In addition to the plane now exposed in the cliff face there are others running at all sorts of angles --  one of them is running more or less horizontally, and as we can see in the photo it has given rise to a newly-formed bench or platform a couple of metres above present HWM, where big slabs have broken off and then been smashed up.

Archaeologists please note -- this is NOT a Neolithic quarry made by intrepid seamen who shipped all their handy slabs of rock off along the coast in curraghs or log boats.  A flat rock face with big detached slabs beneath it does not make a quarry.....

But there has been some opportunist human interference, as we can see from the graffiti!

Abermawr raised beach exposure

The raised beach location at the northern end of Abermawr.  Click to enlarge if you have difficulty in seeing the detail or reading the text...

Today I was at Abermawr in the hope of getting a good look at the raised beach that I spotted back in the spring.  Unfortunately it was high tide, and the waves were crashing around the foot of the cliffs.  I got as close as I could, and I think the exposure is still there, as marked on the photo above.  The beach pebbles seem to be resting on an undulating raised beach platform, and the dark patch in the photo may well be a part of the beach which is cemented with manganese and iron oxide cement.  Need to get up there to examine it properly one day.........

The beach pebbles, which seem to be in a sandy matrix, are in a layer about 50 cms thick.  They are sealed beneath the thick Lower Head (the Early and Middle Devensian periglacial slope deposit).  And above that are the reddish brown flow tills and fluvio-glacial sands and gravels dating from the Devensian glacial episode of about 20,000 years ago. And above that are mixed solifluxion deposits, brickearth and blown sand.

Mt guess is that the raised beacj is from the last interglacial, which makes it around 100,000 yars old.

Here is another pic, taken from the clifftop to the north:


Mystery erratic from Abermawr, Pembs



This is a strange one -- never seen anything like it before.  Does anybody recognize it?  It was lying on the pebble beach at Abermawr, having obviously dropped out of the Irish Sea Till exposed in the cliff.  Anglesey?  Isle of Man?  Lake District?  Scotland?  Definitely not Pembrokeshire......

It's very smooth and silky to the touch -- highly silicified? The subtle colouring and sirface texture reminds me of some of the glassy rhyolites found in N Pembs -- but those big brecciated fragments make me thing it might be an ignimbrite or something on those lines....







Thursday, 2 October 2014

Is Flat Holm a roche moutonnee?

Flat Holm as seen from Steep Holm -- looking north.  In this view the asymmetrical profile of the island is striking.  The Anglian Irish Sea Glacier travelled from left to right.

An oblique aerial photo of the island, looking from north towards south.  Here again the cross profile is obvious.  The steep cliffs are to the left on the down-glacier side, and the gently rising land surface is on the right, on the up-glacier side.

In this vertical image, the south is at the bottom and the north is at the top.  Once again we see the steep cliffs to the right, between Castle Rock and Lighthouse Point.  The west coast is very different, with a large area of reefs exposed at low tide and a very low cliff line.

This all looks pretty convincing.  However, we must be aware that there is some structural control here, because the most dominant structural feature on the island is a pitching anticline in the Carboniferous Limestone bedrock, which runs roughly NE-SW across the island.

Bristol Channel Palaeolandscapes

This is an earlier post of mine, from 2011, which is very relevant for our discussion on the sequence of events at Flat Holm:

http://brian-mountainman.blogspot.co.uk/2011/10/west-coast-palaeolandscapes.html



WEST COAST PALAEOLANDSCAPES SURVEY  (WCPS)
2011
By Simon Fitch and Vince Gaffney With Contributions from Eleanor Ramsey and Emma Kitchen
(Visual and Spatial Technology Centre Institute of Archaeology and Antiquity, University of Birmingham, Birmingham, B15 2TT)

The West Coast Palaeolandscapes Project partner’s WWW pages can be accessed at:
Dyfed Archaeological Trust: http://www.cambria.org.uk/lostlandscapes/index.html
University of Birmingham: http://archaeologydataservice.ac.uk/archives/view/wcpp_eh_2011/
Royal Commission on the Ancient and Historical Monuments of Wales: http://www.rcahmw.gov.uk/HI/ENG/Heritage+of+Wales/Maritime+Archaeology+In+Wales/

There is a great deal of detail in the report, which deals with Liverpool Bay and the Bristol Channel area.  It's a pity that in the latter research area, the work was not extended eastwards to the islands of Flat Holm and Steep Holm, which are conventionally taken as being situated at the junction between the Severn Estuary and the Bristol Channel.   Here are the two key maps:

This is the reconstructed situation in the Late Upper Palaeolithic, after the Devensian Glaciation but before the sea had started its incursion into the area now known as the Bristol Channel.

During the Mesolithic (after 10,000 yrs BP) the sea was flooding eastwards, gradually converting freshwater lagoons and lakes into brackish water bodies and then extensions of the sea, forcing rapid ecological and landscape change.

As far as sediment types are concerned, the following two maps are instructive:


http://webarchive.nationalarchives.gov.uk/20121217150421/http://decc.gov.uk/assets/decc/What%20we%20do/UK%20energy%20supply/Energy%20mix/Renewable%20energy/Severn%20Tidal%20Power%20feasibility%20study/1_20090710143419_e_@@_SevernTidalPowerScopingTopicPaperHydraulicsandGeomorphology.pdf

DECC --  SEVERN TIDAL POWER - SCOPING TOPIC PAPER Hydraulics and Geomorphology

Note from the upper map of this pair that the only area where glacial till is dominant on the sea bed is a strip c 5 kms offshore of the Somerset coast near Minehead and Porlock.  It's not known whether this strip extends all the way to Lundy Island.  Perhaps surprisingly, there are no sea-floor expanses of glacial till off the Glamorgan coast in those areas that might have been affected by piedmont glacier lobes at the time the maximum Devensian glaciation.  That is not to say that such material is absent -- it might of course be buried beneath finer sediments. Closer to Flat Holm there are patches of sandy and gravelly materials on the sea bed, and extensive areas of exposed bedrock.  Sediments in and around the deep channel which runs between Flat Holm and Steep Holm are generally less than 10m thick.

So if there are glacial erratics on Flat Holm, what is their source?  Watch this space......






Wednesday, 1 October 2014

Strangeness in Alberta



Abraham Lake in Alberta is an artificial lake in which a very strange phenomena occurs every winter.  When the temperatures are -30 deg C it is too cold for snow in this arid environment, and as the water surface freezes a thick layer of completely clear ice develops, up to 30 cms thick.  Methane -- maybe from old beds of rotting vegetation on the lake floor -- bubbles up to the surface, and when these bubbles reach the base of the surface ice they expand, flatten out and freeze.  Then they stack up (or stack down) like dinner plates or saucers in a pile.  Apparently you can easily walk over this ice surface, but because the ice cracks and moves, and is as clear as glass, it can be a seriously weird and frightening experience.........

Photo:  Chip Phillips