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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Monday, 31 August 2015

Felindre Farchog enclosure

Apologies to Pembs Hist Soc -- I thought they were referring to an enclosure called Castell Mawr.  Probably it is this one, which is actually on the valley floor:,+ENCLOSURE/

Thanks to Geo for pointing this out.  You can easily find it on Google Earth or "Where's the Path?"

So there will be some digging there in September -- I wonder if Castell Mawr has been abandoned?

Sunday, 30 August 2015

All aboard the fantasy waggon.....

One of our esteemed contributors has alerted me to this.  Copied below.  On the Pembs Hist Soc web site, they even used one of my illustrations, which I thought was a bit cheeky.  But in my magnanimity I forgive them. (Of course, I use other people's illustrations all the time!)

This is all news to me, since I am not a member of the Historical Society, although their journal has published articles by me in the past.

Isn't it amazing how even sombre and steady historians get swept away by the mythology of the day?  Just look at these bits from the blurb:

Prof MPP "...... has been working at both ends of the conundrum, and in conjunction with scientists and geologists has succeeded in pinpointing the precise origins in the Preselis of some of the Stonehenge bluestones."  Not sure that the good Professor has done any of that,  and I'm not sure what exactly is meant by "precise".......

"CARN GOEDOG and CRAIG RHOS-Y-FELIN, have been identified by geologists Richard Bevins (National Museum of Wales) and Rob Ixer (University of Leicester) as sources for some of Stonehenge’s bluestones. Craig Rhos-y-felin, a remarkable rhyolite outcrop, provided probably just one monolith; the geologists have been able to identify the precise spot it was taken from."  Dodgy statement from top to bottom.  A little less certainty might just have been a good idea......

At Carn Goedog "......... evidence has been found for removal of many pillars from this site in the Neolithic period."  What?  What evidence?

"At the foot of Carn Goedog are numerous hut platforms........"  Numerous?  Four or five, maybe, and "a few" might be a rather better expression...... but I feel a village coming on.

So there we go.  When the fantasy waggon is rolling, look how easy it is to hop aboard and enjoy the ride! Yahoo!!

Luckily I am elsewhere on Saturday, meeting up with a book club in New Quay.  But if anybody else wants to go along, I'm sure you would be very welcome.


When Faith moved Mountains

Field Trip with Prof. Mike Parker-Pearson

Saturday, 5 September 2015

If you have been following the Stonehenge story in recent years, then this field trip is not to be missed.

The mysterious and improbable link between Pembrokeshire and Stonehenge has given rise to many hotly contested theories. For over 90 years, ever since the source of the bluestones in that enigmatic monument was traced to the Preseli Hills, controversy and speculation have reigned.

Over the last few years, Professor Mike Parker-Pearson of the Institute of Archaeology, University College London, has been working at both ends of the conundrum, and in conjunction with scientists and geologists has succeeded in pinpointing the precise origins in the Preselis of some of the Stonehenge bluestones. This year he is excavating at three Pembrokeshire sites and has very kindly offered to give us a guided tour of them.

Two, CARN GOEDOG and CRAIG RHOS-Y-FELIN, have been identified by geologists Richard Bevins (National Museum of Wales) and Rob Ixer (University of Leicester) as sources for some of Stonehenge’s bluestones. Craig Rhos-y-felin, a remarkable rhyolite outcrop, provided probably just one monolith; the geologists have been able to identify the precise spot it was taken from.

High on the Preselis, Carn Goedog has been identified by Richard and Rob as the dominant source for Stonehenge’s spotted dolerite monoliths and evidence has been found for removal of many pillars from this site in the Neolithic period. At the foot of Carn Goedog are numerous hut platforms, one of which is being excavated to see if it was associated with the Neolithic quarrying.

The third site we will be visiting is at FELINDRE FARCHOG, on the valley floor of the River Nevern (Nyfer) where a circular enclosure is being excavated to find out if it dates to the Neolithic.

The itinerary:

Meet at the Salutation Inn, Felindre Farchog at 10.00 a.m.
Visit the excavation there.
Go on to Craig Rhos-y-Felin.
Return to the Salutation for refreshments (approx. 12.00 p.m.) and to hear a short talk from Mike on the discoveries at Carn Goedog for the benefit of those not able to make the journey.
Approx. 1.30 p.m. the Carn Goedog party leave, weather permitting. This site is a 45 minute trek each way over steep rough ground. While I am sure some of you are well able to cope with hill walking, please note that you do it entirely at your own risk. The Society cannot be held liable for any loss or injury.

Please contact the Secretary, Ann Sayer (01348 811614 or if you would like to join all or part of this field trip.

Saturday, 29 August 2015

More geomorphologists visit Craig Rhosyfelin

Dr Rick Shakesby, Dr John Hiemstra and Dr Simon Carr in good form at Craig Rhosyfelin yesterday.  Following the encouraging note from the Quaternary Research Association for members to take a look at the dig site, it's gratifying that a number of specialists in glacial geomorphology and related disciplines have now made visits.   Some have visited in my company and others have been there independently, including at least one group with students. The more the merrier!

Next week, I gather that Prof MPP and his team will move in and start the 2015 dig season. I really hope that while it is going on, more geomorphologists will take the opportunity of calling in and passing on their thoughts as to the nature of what they are looking at.......

I have no information as to what will happen to the site at the end of the 2015 dig.  It will be helpful if at least part of it is left open so that some proper geomorphological research can be undertaken.

Friday, 28 August 2015

Red sandstone erratics at Newport

I went for a walk on the shoreline of the Nevern Estuary yesterday (while my car was failing its MOT test) and when I wandered across the exposures of till exposed between HWM and LWM I was once again amazed by the frequency of red sandstone erratic cobbles and pebbles.

The colouring varies from purple through red towards the pink end of the scale, and the rocks vary in texture too -- some are coarse and some are fine-grained. But I did not see anything resembling a true red marl.  Some cobbles are more like gritstones than sandstones.

So where on earth have they come from?  I doubt that they can be from any of the Old Red Sandstone outcrops in the UK, since there is no evidence (so far as I know) of ice movements from any of those areas towards North Pembrokeshire.  The cobbles cannot have come from the red and purple Cambrian Sandstones of the St David's area either -- since that would have involved ice moving from the SW towards the NE.

So one has to assume that the sandstones are from the Lower Cambrian deposits around the Harlech Dome in North Wales -- maybe carried initially by Welsh ice flowing westwards of south-westwards from the Welsh Ice Cap, and then picked and transported southwards by the Irish sea Glacier.  A nice little puzzle.....

Note added:  With regard to the Harlech Dome rocks, they are the right age, but are they the right colour?  Hmm -- as far as I can see from some investigations,  there are no red sandstones in the sequence.  More and more intriguing.

Meltwater moulding of rock surfaces

I thought this was worth sharing -- an amazing image of the moulded bedrock floor of a subglacial meltwater channel -- near the snout of Bruarjokull in Iceland.

These "moulding" features are not often seen, but they do occur at Rhosyfelin, and I am still not sure whether they are very old (ie associated with the cutting of the meltwater channels, probably in the Anglian Glaciation) or relatively young (ie associated with the Late Devensian meltwater flowing in the vicinity at the time of the deposition of those torrential meltwater deposits near the tip of the rocky spur).

Wednesday, 26 August 2015

Expanding settlement in Wales

Here are three more maps from the SEA6 report (2005).  The maps are ten years old, but still pretty accurate.  They show the extent of settlement, so far as we can interpret it from archaeological traces, in the Palaeolithic, Mesolithic and Neolithic periods.

The Palaeolithic lasted for a very long time, and the main cave sites are associated for the most part with the outcrops of Carboniferous Limestone.  People were certainly living in Wales around the time of maximum ice extent during the Devensian (23,000 - 20,000 yrs BP).  They lived close to the ice edge, and probably at times within sight of it, and prior to the maximum extent of the Welsh Ice cap and the Irish Sea Glacier they must have lived within the "glaciated area" as the ice advanced and forced them southwards.  Many of their settlement sites will have been obliterated or buried -- some will certainly be discovered in the future.

By the time of the Mesolithic people must have re-established themselves right across Wales.  Did they live preferentially close to the coasts?  Maybe, because movement was easier there, and because fishing could supplement food supplies, but we see that there are also many settlement sites far inland, and I assume that there must have been thousands of others -- maybe also including Rhosyfelin?  Some will have been ephemeral, and others must have been permanently occupied.

In the Neolithic there were hundreds if not thousands of settlement sites all over the place.  There is not much evidence that the coast was preferred......

All of this evidence summarised in the maps must be interpreted with caution, since much of it is based upon "chance" discoveries, and agricultural practices within the last few centuries have certainly obliterated vast numbers of sites.  So in some areas an assumption that Neolithic people preferred uplands or "wild places" must be taken with a pinch of salt......

Another Doggerland map

This is a really good map which represents Doggerland rather more accurately than some others.  Courtesy National Geographic.  It suggests that the maximum extent of this "expanded British Isles" occurred around 18,000 years ago, and that by 10,000 years ago Doggerland was already much diminished in size. 

There are lots of factors to take into account in working out how big this dry and ice-free area was -- isostatic depression, eustatic sea-level rise as water was returned to the oceans, the actual extent of glacier ice and snowfields, and even the extent of marshes and lakes, which must have been very extensive at times.  Perhaps we should also give a name to the vast area to the South-West as well -- incorporating the Celtic Sea and the English Channel, and even extending well south into the Bay of Biscay. Suggestions on a post-card please.......

Prehistory and the Irish Sea

Thanks to Chris for alerting me to this, which I had never seen before.  Full of very interesting information, although a lot of it is rather dated.

The scope of Strategic Environmental Assessment of Irish Sea Area SEA6 in regard to prehistoric archaeological remains
N C Flemming, Sheets Heath, Sheets Heath Common, Brookwood, Surrey, GU24 OEN.
This document was produced as part of the UK Department of Trade and Industry's offshore energy Strategic Environmental Assessment programme. The SEA programme is funded and managed by the DTI and coordinated on their behalf by Geotek Ltd and Hartley Anderson Ltd.
March 2005

Obviously the emphasis is on the Irish Sea itself, and the sea floor features, but there is a great deal of splendidly presented map information, with some maps drawn specifically for this publication.  They are worth sharing, with full acknowledgement as to the source.

This is one of the maps, which shows Doggerland in the "late-glacial"  -- which I assume means the time at which the last remnant of the Devensian ice sheet occupied the west coast of Scotland.  Alternatively the map might represent the situation in the Younger Dryas -- the time of the Loch Lomond Readvance (c 10,800 yrs BP) and the last occasion on which there was a recognisable ice sheet remnant over western Scotland.  If that;s the case, the ice sheet remnant should have been located a bit further to the east, leaving the Hebrides largely ice-free.

These two maps are also very informative, showing the extents of the Anglian and Devensian  ice sheets over Britain and Ireland:

The precise ice limits are not very accurate -- since this map was drawn around ten years ago a lot of papers have been published to redefine the positions of these limits in various parts of the UK and Ireland. 

One thing I do like about the Anglian glaciation map is the portrayal of ice movements in the Celtic Sea arena -- the arrows are much more realistic than those shown in some other reconstructions.

Monday, 24 August 2015

So what did Rhosyfelin look like?

An ancient photo taken in 1960 at the snout of the Kaldalon Glacier in NW Iceland.  Me and my mates Keith and Dave.  I'm the one on the left.

I was trying to illustrate the other day what I thought the environment might have looked like at Rhosyfelin at the time of Devensian ice wastage.  Well, this image illustrates it pretty accurately.  Boulders, gravels, silts, clays, till, ice and lots of water flowing rather fast........

Friday, 21 August 2015

More on the Stonehenge "periglacial stripes"

Thanks to Chris Johnson and Tony Marsh for alerting me to this.   Thanks also to Geomatics PLC.   It's a new LIDAR image of Stonehenge and the Avenue, showing the ground surface contours at 1 ft intervals -- this is very detailed work.

So what does it show us that we did not know before?  We have discussed to so-called "periglacial stripes" at great length -- use the search box for the relevant entries.  I am happy to admit that I have got it wrong -- I have interpreted the "grain" of earlier LIDAR images as showing that the alignment of the Avenue and the "periglacial stripes" is oblique to the prevailing surface slope.  This new image shows that the alignment is in fact perpendicular to the contours.  In other words, the Avenue runs pretty well exactly along the "nose" of a very slight ridge, except at its outer end, where it simply keeps going in a straight line to the far end of the spur.  So there it is on the flank of the spur rather than on the ridge top.

Tony has added the T-marks on the image so that we can see where averaged perpendiculars are located -- but these are subjective in the sense that the alignment of the downslope line will vary according to the width of the lateral spread of the sampled points.  If you see what I mean.......

We are talking about very subtle variations here -- just a degree or two.  So the message is that the Avenue has been build along the nose of the ridge, and maybe has nothing at all to do with solar or lunar alignments of solstices.  By the same token, the "periglacial stripes" are running pretty well directly downslope, as we would expect them to do in a periglacial environment.  But I still don't think they are anything to do with periglacial sorting or patterned ground processes.  They are not straight, and because of their internal characteristics I still think they are solutional rills just like the many thousands of others in the Stonehenge landscape.  Here -- at the SW end of the Avenue -- they  run pretty well parallel to the Avenue sides.  To left and to right they probably splay slightly, keeping more or less perpendicular to the contours and running directly downslope so long as there is a sufficient gradient.  That is what water does.

The trouble is that nobody has looked for these "insignificant" or "irrelevant" rills systematically, because the focus of attention has always been Stonehenge and the Avenue.

A fantastic image of the excavation that exposed these mysterious rills within the confines of the Avenue.  Courtesy Aerial Cam and  We can see that they are not straight, in cross-section we see two different wavelengths.  There are two gentle ridges with a hollow between them, and superimposed on those we see smaller rills which wind or weave their way downslope.   This all suggests that solution has been the prime process, and that water has been the agent of land surface change.  This is exactly what we would expect on gently undulating chalkland such as this.

Sunday, 16 August 2015

Periglacial Preseli

 The Preseli winter landscape.  This image (not very good definition) shows a scattered snow-cover on Foel Drygarn (in the foreground) and eastwards along the Preseli ridge.  Carningli and the sea can be seen in the far distance.

Chris was asking the other day what Preseli might have looked like during the "missing millennia" between 18,000 yrs BP (when we can rather safely assume that the last of the glacier ice in the region had melted away) and the Neolithic, around 5,000 yrs BP (when we can safely assume that the resident population was large enough for the human impacts on landscape, through burning, animal grazing etc were big enough to make a real impact). 

Well, for most of the time a periglacial climate must have dominated, as suggested in my post of 3 January 2013:

A bleak tundra landscape would not have looked all that different from the Preseli winter landscape of today, except that "high arctic" vegetation would have been more prominent than the grassland - moorland which we see today.

The only major change which we can assume from the climate records is that of the Younger Dryas, around 13,000 years ago, when for a thousand years or so temperatures plummeted, snow-cover increased and there was a "mini Ice Age."  Chris asked whether glaciers might have been re-formed on Preseli at this time, and whether glacier ice could have affected Rhosyfelin.  I don't see any evidence that suggests this -- but it is quite possible that for some centuries there were permanent snow patches and neve fields, and possibly one or two "niche glaciers" in places like Cwm Cerwyn, which left very subtle traces when they finally melted.

See this post:

See also this post on Rosemergy niche glacier:

You will also see in that 2012 post that I date the Younger Dryas at around 10,500 BP.  A few years ago it was still common to refer to Zones 1-3 and the Older Dryas (cold), Allerod interstadial (warmer), and Younger Dryas (cold) phases.  That sequence can be picked up in some sedimentary sequences on the continent, but it is difficult to recognise in Britain, and so nowadays geomorphologists and palaeobotanists tend to refer to a singe "cold snap" that might have had  oscillations within it which were not necessary in phase all over the British Isles.

Baby Glacier on Axel Heiberg Island, a typical niche glacier.  This has real glacier ice at its core, showing that it is probably rather old.  The Younger Dryas niche glaciers in Wales were much more ephemeral.

Summer landscape near Honningsvag, Norway.  Upland Pembrokeshire might have looked like this during the Younger Dryas, with a  mosaic of temporary (seasonal) snowpatches, perennial snowpatches, neve fields and niche glaciers.

Thursday, 13 August 2015

Mammoths on Preseli

Only joking -- couldn't resist putting this post up.  It's a fantastic image from today's BBC web site.  An illustration from the Natural History Museum.  Very graphic -- and I'm sure those hills are the undulating summits of Mynydd Preseli.

I have always dreamed of finding a mammoth bone, or a tusk, in some of the Pembrokeshire deposits.  Prefectly possible -- mammoths would certainly have been roaming along the Devensian ice edge c 20,000 years ago.  In most of the world they became extinct by 10,000 BP, but a small population survived on Wrangel Island until about 4500 BP.

Wednesday, 12 August 2015

Rhosyfelin: Once upon a time in the west......

When I was teaching glacial geomorphology, I always found it useful to show students what certain types of glacial environments looked like in the past, by using parallels from today.  Analogies are always good, although of course none of them can exactly replicate the conditions you are trying to work out when you look at a glaciated landscape or a set of sediments.

Anyway, I am pretty convinced that at the time when the till and fluvio-glacial materials were being laid down at Rhosyfelin, about 20,000 years ago, the valley at Rhosyfelin would have looked rather like this:

In these ice-contact or glacier snout environments, we see vast amounts of till, water-carried sediments including boulders, cobbles, sands, gravels, silts and clays -- all mixed up together in very complex relationships.  Small lakes form quickly and drain quickly. These are very dynamic and dangerous environments because buried ice is melting, causing slopes to be very unstable.  "Catastrophic" events are commonplace.

I have seen the sorts of deposits we see at Rhosyfelin in many environments like this, in Greenland, Axel Heiberg, Norway, Iceland and Antarctica.

At Rhosyfelin, these glacial and fluvioglacial deposits seem to be intercalated with rockfall materials and buried beneath up to 2m of stony and pseudo-stratified slope deposits, accumulated over the past 20,000 years or so.  There are signs of water-lain deposits not far from the tip of the spur, suggestive of temporary lakes in the main channel.  The big "proto-orthostat" at Rhosyfelin seems to rest on these "glacial environment" deposits, and following its emplacement in a rockfall it was then buried beneath slope deposits.

If the archaeologists try to tell you that all the sediments around and on top of the big stone were laid down within the past 5,000 years or so, don't believe them.

Sunday, 9 August 2015

New paperback: The Stonehenge Landscape

Thanks to Tony for drawing attention to this new book, which was published in July.  Looks very interesting.......

There is a review in "British Archaeology" by Mike Pitts (Sept / Oct issue, p 54) which highlights a number of interesting issues.  The book summarises many of the free online publications arising from recent EH work -- we have referred to some on this blog.  The argument is given for the use of LOCAL sarsen stones at Stonehenge, rather than sarsens carried or pulled all the way from the Marlborough Downs / Vale of Pewsey.  Apparently there is also an examination of the question "Was Stonehenge ever finished?" -- or at least "Was the sarsen stone setting ever finished?"

There are clear signs here that the authors of this book are rather sensible people!  And even more to my liking is the idea that Stonehenge was created by "trial, error and humour".  I love it!  I have always had a feeling that Stonehenge was a folly, and now I am even more convinced.......

All that having been said, I have obviously not read the book -- so if anybody wants to add a review or report on it in detail, let me know....

Friday, 7 August 2015

Water-worn quartz outcrop at Rhosyfelin Ford

This is interesting -- I had not spotted it before.  It's a 2m long outcrop of pure white quartz in the wood not far from the Rhosyfelin Ford, on the other side of the road from the archaeological dig site.  I suspect it is a bedrock outcrop rather than a detached mass, but without excavation it's difficult to be sure.  It may well be a part of the quartz vein which we see in the crag and near the big slab which has caused so much excitement.

What is interesting about it is the extraordinary degree of moulding and smoothing there has been on the surface.  Again, a clear indication that there has been very powerful meltwater flow on the floor of this valley in association with ice wastage at the end of the Devensian glaciation.

Rhyolite erratics from Devon

 These boulders (some of them are made of local foliated rhyolite) have not travelled far.  In fact, they are still at Rhosyfelin, rounded by ice and water to varying degrees.  Wouldn't it be interesting if some similar boulders had been transported to the coast of Devon?

A reminder of this post, and of the work of Paul Madgett and others in Devon, revealing the presence of rather a lot of erratic boulders in places where they could not have been transported by ice floes..........

Here is a part of Paul's list of erratics from the Croyde area:

Note that there are several boulders of "rhyolitic tuff" in this list, namely numbers 10, 19, and 37, with others described as rhyolite (31) or tuff (13, 20 and 33).  Sometimes it is difficult to classify a rock type simply from examining the weathered surface of a rounded boulder -- but wouldn't it be interesting if one or two of these -- or maybe even more -- should turn out to be made of foliated rhyolite from Rhosyfelin? 

We need some samples -- but I would not be at all surprised if rhyolite boulders and fragments from the Rhosyfelin - Pont Saeson area had been transported by Anglian ice into Devon and Somerset.

Rhosyfelin: manufacturing a Holy Grail

 After two months abroad, I called in at Rhosyfelin today, and this was how the big stone and its wrapping looked.  Wrapped up for protection from prying eyes.....

Not long ago I picked up from a rather senior figure in the Pembrokeshire Coast National Park Authority (PCNPA) that some sort of planning is in process for the designation of Craig Rhosyfelin as a key "heritage site"  -- one of the jewels in the crown which will be publicised mercilessly as Pembrokeshire seeks to show the world just how important it is in terms of archaeology and prehistoric heritage.  The tourism business in the UK is highly competitive these days, and you have to promote your assets for all you are worth, if you are to compete with other regions which also depend -- to an ever-increasing extent -- upon tourist income during the summer months.  So to hell with good science and the truth -- this is all about marketing and commercial advantage.

I reminded said senior figure that Rhosyfelin is not a Scheduled Ancient Monument, that there is no prospect of it being declared one, and that there is nothing in print (peer reviewed or otherwise) to demonstrate that there is anything at all here which is of archaeological interest, let alone a Neolithic Bluestone Quarry.  My letter to said senior figure has not elicited a reply.  That reminds me of the occasion, a couple of years ago, when I sought to correct some of the things put about by Phil Bennett, the senior archaeologist at the National Park, about Rhosyfelin:

My letter was ignored by Phil, and although I have reminded him about it subsequently, it remains ignored.  I am less than impressed.  And in the time that has passed since the start of the Rhosyfelin dig in 2011,  certain people have hoofed about on the lecture circuit, enthusiastically promoting the idea that the evidence from Rhosyfelin is "the smoking gun" in the bluestone transport debate, and that this site is "the Pompeii of prehistoric stone quarries"...........

Unstoppable momentum?  So it would appear, when nobody, apparently, wants to look at evidence and everybody, for their own reasons, wants a marketable product.  Of course, Rhosyfelin is highly marketable.  Who would not be interested in a Neolithic Bluestone Quarry?  So public access and visitor enjoyment have to be encouraged and enhanced, and things must be visible enough for the public to enjoy.  And clearly, as a part of this strategy, THE BIG STONE has to be the prime exhibit.  It is already designated as the Holy Grail, and on that basis it must be protected and nurtured -- and the mystique surrounding it has to be built up, bit by bit, until it is finally revealed to the world in a blaze of glory.  Just a reminder that we have seen it before, and that it looks like this:

Shock!  Horror!  People actually standing on the Holy Grail, and one of them rolling a ciggy at the same time.........  whatever next?  Well, the National Park (I presume) has tried to protect the stone from such blatant abuse on two previous occasions, so far as I am aware.  This is what it looked like last time:

At the time, I joked about the black plastic looking like a shroud, thinking that the stone was going to be reburied with full archaeological honours before very long.  But no, the black plastic (which was of course very quickly removed by inquisitive passers-by) was there for a much higher purpose, namely the protection of a valuable if not iconic object, to be protected at all costs.

I am still not sure who put the black plastic over the stone, and on whose authority -- but let that pass..........

This all reminds me of that poor little erratic in New Jersey, trapped in an iron cage. Does a similar fate await the famous Rhosyfelin pseudo-proto-orthostat? (It's somewhat larger than this little one, and a crude cage like this, made with concrete reinforcement rods, would never do inside the National Park.  Probably the budget would have to be found for a cage which is designed and created by a genuine master craftsman......)

So what about this amazing pseudo-proto-orthostat which is now to be considered on a par with the Holy Grail?  Let's just remind ourselves that it is completely useless as orthostats go, since it is too heavy (at 8 tonnes, about 4 times heavier than most of the other "bluestones" at Stonehenge; not a particularly useful shape; made of a very splintery and easily-shattered rock type; and so full of fractures that it could not possibly have survived transport out of the Brynberian Valley, let alone transport all the way to Stonehenge.  Also, let's remind ourselves that there is no evidence from anywhere that the Rhosyfelin foliated rhyolite was valued in any way as a rock suitable for orthostats, single standing stones, or cromlech pillars or capstones.  I know of no other prehistoric monument that used this foliated rhyolite -- and I suspect that is because no Neolithic stone-worker would have considered for a moment that it was worth using.  Maybe for cutting tools, but not for sticking in the ground as a pillar, for some ritual purpose or other.

The transverse fracture running across the face of the Rhosyfelin big slab.  It runs deep into the heart of the stone, perpendicular to the foliation planes in the rock.  The block is in grave danger of breaking in half.

So the fantasy rolls on -- and as it rolls by, more and more people jump on board, partly because they defer to the opinions of a certain professor who has a high media profile, and partly because it's good for business.  Some people not far away from here have just opened a little display relating to the prehistory of the area.  It proudly refers to the "Stonehenge Bluestone Quarry" which is over near Brynberian.  When challenged about this, the reply was: "Who cares what the truth is?  People love a heroic  story, and it's good for trade........"

Part of me thinks that none of this actually matters very much, since it's all froth.  But then another part of me thinks: "Whatever happened to scientific methods and academic standards?"

By the way, the National Park has posted a notice saying that the public footpath running past the tip of the Rhosyfelin rock spur will be closed for the month of September, or for the duration of the 2015 dig.  It will not cause any inconvenience to anybody, since a new temporary footpath will be in operation, just a few metres closer to the river.  Access to the dig site will still be very easy.

Tuesday, 4 August 2015

Carreg Coetan and the Enigmatic Dolerites

Now for another enigma.  Where did the dolerite boulders of NE Pembs come from?  It's very easy to explain the presence of dolerite boulders almost everywhere else in Pembrokeshire as a consequence of glacial erratic transport, but in NE Pembs -- in the area between Dinas Island and Cemais Head, incorporating the country around Newport, Moylgrove and Cardigan -- there are dolerite boulders dotted around here and there which cannot easily be explained by reference to the glacial maps.  Many years ago the geologist OT Jones pondered on their presence.  The ice during the Devensian glaciation came in from the N and NW, having crossed the area now known as Cardigan Bay.  As far as we know, all of the dolerite intrusions associated with the Fishguard Volcanic Series are to the south of Newport (see the BGS map above), and so they could not have been picked up and moved northwards by ice  moving in the opposite direction!!

There are some possible explanations.

Maybe the dolerite boulders in the area have come from dolerite exposures in the Pen Caer - Strumble Head area by ice moving directly west - east.  There are some dolerite outcrops on the peninsula.  We know from striations on the coast that the ice did move in this direction at some stage.

Another possibility is that the dolerites have come from the Cader Idris area, or even North Wales, and were transported by Welsh ice and Irish Sea ice before being dumped in this area.

A third possibility is that they have come from dolerite outcrops which are now beneath the sea bed.  This seems quite feasible, given that the Penyraber and Cwm-yr-Eglwys mudstone formations are right at the base of the sedimentary sequence overlying the Fishguard Volcanics.  There are complex faults in the area, and I am sure there are some igneous rocks exposed in the cliff faces of Newport Bay, although they are not shown on geological maps.

A fourth possibility is that the boulders are really from the Preseli outcrops, and that they have been transported northwards by ice flowing from a Preseli ice cap either before or after the Devensian LGM of Last Glacial Maximum.  There are a few anolalies in the evidence, and I have suggested several times on this blog that at some stage Welsh ice crossed North Pembrokeshire, flowing from the east towards the west.  But it's doubtful that such ice would have carried dolerite boulders, for the prevailing rock types to the east are Ordovician and Silurian sedimentary rocks -- sandstones, gritstones, shales and mudstones.

Then a fifth possibility.  Could the stones have been transported to the locations of assorted Neolithic burial chambers and Bronze Age standing stones by prehistoric people?  OT Jones was convinced that assorted dolerite pillars used as gateposts and in house building in this area were in fact collected from the Preseli Hills by landowners and farmers during and after the Middle Ages;  I would go along with that, and there is indeed much evidence of "modern stone gathering"and maybe even quarrying of dolerite outcrops within historical time -- simply because the stones were easy to transport and use.  But if we go back to the Neolithic, the evidence of stone transport is not strong.  Those archaeologists who have looked at the cromlechs of the area -- like Pentre Ifan,  Cerrig y Gof, Llech y Dribedd and Trellyffaint -- have always concluded that the boulders used have been glacial erratics used more or less where they were found.

Carreg Coetan Arthur, in Newport, is a good example.  It is in a small enclosure not far from the estuary, and it incorporates a huge capstone resting on just two uprights.  It is very precariously balanced, and it is a wonder that it has not collapsed.  Two other uprights almost touch the capstone, but daylight is visible at the tip of each stone.

All of the stones at this site (capstone, pillars and several other fallen stones embedded in the turf) are made (as far as I can see) of unspotted dolerite which looks like the dolerite of the Carningli-Newport area, which outcrops just a couple of km to the south.  The stones are well weathered, and have rounded or abraded edges typical of glacial erratics.  So they LOOK like glacial erratics, and they are most certainly not quarried from anywhere.  It has to be assumed that they were used more or less where found.  The massive capstone also has a worn and weathered upper surface and a less weathered and somewhat flaky lower side;  I assume that (as in the case of the Pentre Ifan capstone) it once lay embedded in the ground and may even have been overridden by ice before being exposed and subjected to 15,000 years of weathering.  Then somebody came along with the bright idea of levering it upwards, placing props or pillars beneath it, and making it into a burial chamber......

Was this also the history of the other burial chambers to the north of the Nevern River?  Watch this space....

Saturday, 1 August 2015

Quarrying and entrainment beneath an advancing glacier

While looking at some material relating to the Wisconsin Glaciation of North America, I came across this interesting diagram in the Illinois State Geological Survey web site.

It's interesting because it portrays pretty well the exact scenario that I envisage for the quarrying and entrainment of blocks and other debris from the area around Craig Rhosyfelin in North Pembrokeshire.  What we have in this idealised scenario is an old valley transverse to the direction of advancing ice flow,  with plucking and entrainment along shear planes within the ice.  This enables blocks and other debris to be transported in an englacial situation.

Nothing new under the sun......

North American Ice Sheets

I found this interesting image of the North American Ice Sheets during the last (Wisconsin) glaciation, c 20,000 years ago.  The quality of the image is not very good, but you get the general idea.....

Note that there were four ice sheets, all joined together. (In Antarctica today we see the West Antarctic and East Antarctic Ice Sheets connected in a similar way.)  Note that this was a very extensive glaciation in which the ice edge in many areas progressed beyond the limits of earlier glaciations.  The exception is the area to the SW of the Great Lakes, where earlier glacial deposits are still exposed at the surface.

More detail here:

Map credit:
Dr. Judson L. Ahern
University of Oklahoma