Posting problems

Apologies all for the problems with posting over the last week.  I've just returned from a week in Tuscany (those defended hilltop villages are AMAZING!!) and discovered that my laptop was not picking up the majority of posts -- just some of them.  No idea why.......  anyway, on my return, I found more than 20 posts on my home computer, and have now put all of them onto the site.  There may be some duplication and confusion as a result..... but I hope that a sense of good order will soon return!  Thank you all for your contributions.

The Glaciation of Rhosyfelin

A glacial erratic with a distinct orange-coloured patina -- exposed among the litter on the floor of the 2012 dig at Rhosyfelin

I'm often asked what the evidence of glaciation is in the Rhosyfelin area.  Well, there is plenty of it about.  The upper part of the Brynberian Valley (in which the rocky crag is located) has been glaciated on at least two occasions, and probably more.  The glacial episodes about which we know most were the Anglian (about 450,000 years ago) and the Devensian (reaching its peak around 20,000 years ago.)  The former was almost certainly the time of the GBG (Greatest British Glaciation) and in the latter the Irish Sea Glacier was very extensive and may even have extended beyond the Devensian limit in some areas.  The Wolstonian / Saalian Glaciation was probably extensive, but traces of it are very difficult to differentiate from those of the Devensian, as Chris Clark, Phil Gibbard and many others have pointed out.  So let's put that to one side for the moment, while allowing the possibility that it might have done some work, at the very least, in modifying the landscape of West Wales.

Suggested limit for the Irish Sea Ice in the Devensian period.  The glacier came in from the north and north-west.  The dotted area shows the suggested extent of the Preseli ice cap, which would have been contemporaneous.

During both the Anglian and Devensian glaciations, the ice of the Irish Sea Glacier came into this area from the N and NW.  First, what do we know about the Anglian ice extent?  It has been accepted for more than 100 years that the ice inundated the whole of Pembrokeshire and that it flowed up the Bristol Channel  -- and for well over 50 years it has been known that it impinged upon the coasts of Devon, Cornwall and Somerset.  This is indisputable -- and if any archaeologist or geomorphologist tells you otherwise, do not believe them. So the ice was very thick indeed -- maybe up to 600m thick -- as it flowed across this area.   Was entrainment of blocks of stone or monoliths possible at this time from the crags at Rhosyfelin?  Yes -- without a doubt.  I have covered this possibility -- and indeed likelihood -- many times before on the blog. Large glaciers and ice sheets can and do entrain large blocks on the up-slope flanks of upland barriers where glacier bed conditions are just right.  So entrainment was more likely to have happened on the northern flank of Preseli than either on the summit or on the southern flank, where the glacier bed at the peak of glaciation was most likely to have been frozen to its bed. This is a matter of ice physics or glaciology -- not a lot to do with geology, although obviously tors and rocky crags will have made perfect entrainment locations.  One of the problems with Rhosyfelin is that we do not know how much bigger the pre-glacial crag might have been.  It might well have been 10m or more higher than it is today.  Thousands of tonnes of the famous foliated rhyolite might have been removed.  At the moment, we have no way of telling -- but we are working on it.........

The deep gorges of the Brynberian and Nevern Valleys.  Rhosyfelin is the rocky spur on the western flank of the valley near the base of the photo.  These valleys have many features in common with the subglacial meltwater channel complex of Cwm Gwaun and Nant y Bugail.  There are other rocky crags in the Nevern Valley at Felin y Gigfran.

There is also a strong possibility that the river gorge around Rhosyfelin and Pont Saeson was cut initially during the Anglian Glaciation by torrents of glacial meltwater flowing subglacially or on the edge of a wasting ice mass, as the Irish Sea Glacier was breaking up.  In addition to the main gorge, there is a strange subsidiary channel which is both looped and humped -- and this is typical of the subglacial meltwater channels in North Pembrokeshire.  Sometimes these channels are simply swept clean of debris by the sheer force of meltwater flowing through them, at very high hydrostatic pressures.  I would not fancy the chances of any Anglian deposits (either glacial or fluvioglacial) surviving in the area, given that almost half a million years has elapsed -- but I would not rule this out entirely.

This brings us to the extraordinary flat face of the Rhosyfelin cliff -- revealed in spectacular fashion as a result of the recent dig.  This does not look to me like a quarried face, and I am currently convinced that it is a long glaciated face, fashioned above all else by moving ice.  I have not seen any striae on the face -- but I have not spent enough time there, and one day I'll go back and take a closer look. Of course, if there are striations on the face, they are just as likely to be Devensian as Anglian -- given that the ice has returned for a second (or third, or fourth) time to the same area.  One intriguing feature is that the direction of ice movement -- as far as we know -- was broadly from the NW towards the SE, which was perpendicular to the alignment of the Rhosyfelin rocky ridge.  So the natural direction for subglacial meltwater flow would have been up the Brynberian Valley rather than down it, if the dictates of hydrostatic pressure were followed.  It is more likely, given these facts, that meltwater flow was marginal, along or near the ice front of a melting glacier.

Did the Irish Sea Glacier cover this area during the Devensian?  I am increasingly convinced that it did (see the map above), and that the ice edge was somewhere to the south of Rhosyfelin, on the northern face of Preseli.  This assumption is based on a lot of evidence, including the presence of apparently fresh striations on Carn Alw, the presence of apparent marginal channels along the hillsides near Carn Goedog, and the fresh moraine near Tafarn Bwlch and Waun Mawn.  There must have been a great lobe of ice pressing in from the N and NW and filling the depression in which Brynberian and Rhosyfelin sit.  As indicated in earlier posts, some geomorphologists have speculated that there was a marginal lake in this depression either prior to the maximum ice advance, or shortly afterwards.  We await detailed stratigraphy and analysis of the sediments in this depression -- all will be revealed in due course.  There is a layer at the base of the sediment sequence exposed during the 2012 excavation which looks as if it might be lacustrine -- I did not have time to examine it properly.  It's only a few centimetres thick --  was it laid down at the bottom of this large proglacial "Lake Brynberian", or maybe on the bed of a much smaller lake confined within the valley, held up my a plug of melting ice somewhere to the north of Rhosyfelin?

The exposures on the flank of the 2012 dig.  There are many layers in the sediments, although the boundaries between them are diffuse.  The finest-grained deposits are at the base of the section, and may indicate lacustrine or slackwater deposition.  Note the accumulated litter in the foreground, where quite large blocks have accumulated beneath the cliff face.

What about the Late Devensian history of the Rhosyfelin area?  Well, we know that there is a great litter of broken debris beneath the cliff face, as we would expect beneath any steep rock face in Pembrokeshire.  If analogies around the Pembrokeshire coast are anything to go by, this litter must have accumulated after about 20,000 BP, with a late peak of frost shattering and periglacial activity around Zone III or the Younger Dryas, around 13,000 - 11,000 BP.  After the melting of the Irish Sea Glacier in this area, we might well have had 10,000 years or more of oscillating cold climate during which considerable damage might have been done to the Rhosyfelin crag -- so it is very difficult to imagine what it might have looked like during the glacier melt episode.

Several points emerge from an examination of the 2012 dig:

1.  The litter of broken rock seems to me to be entirely natural -- including the placement and positioning of the "big Rhosyfelin orthostat."

2.  I think that the dig might now have got down to the top of a till layer.  There are signs of erratic blocks in the litter -- including at least five big blocks of quartz (which might of course be rather local) and a stone with a yellowing surface patina which does not look like a lump of Rhosyfelin rhyolite (see photo at the top of this post).

Four quartz erratics exposed on the floor of the dig.  We do not currently know how far these might have travelled.  The are sub-rounded, and have been subjected to some wear during transport.

3.  I have not seen any sign thus far of any fluvio-glacial material, although I would not rule this out when the dig goes a bit deeper.

4.  A very intriguing feature of the exposed surface of the litter is the degree of rounding or smoothing that appears on the edges of many of the stones.  Naturally, this foliated rhyolite breaks down into fragments and slabs with rather sharp edges -- so something must have been responsible for the wear on the edges.  The only two candidates, realistically, are overriding ice and meltwater flow.  The former is, I think, a possibility, given that the till layer is now being exposed; the stones which we now see at the dig surface may have come from some distance away, or they might just have been overridden in situ. Some accurate provenancing is needed to sort this out!   Another explanation is that there has been a long process of rounding of stone edges by snowmelt, maybe during the many centuries during which frost shattering and scree accumulation were going on.  (I have to admit that I'm a bit confused here -- more work is needed.)

The rounded upper surface of one of the local rhyolite slabs exposed on the floor of the 2012 dig.  Many stones of all sizes are rounded in similar fashion.  What caused this rounding?  Overriding ice, or glacial meltwater?

5.  The thickness of accumulated slope deposits here is quite surprising, given the relatively short length and limited height of the slope to the NW of the dig site (that is the orientation of the steepest part of the slope.)  As mentioned above, the deposit with the finest and most consistent grain size is near the base of the 2m or so of exposed deposits, suggesting a temporary lacustrine or alluvial situation with relatively low-velocity water flow.  Above that, the sequence of deposits is complex, with a great deal of soil and slopewash material mixed with angular fragments, most of which are presumably rather local in origin.  There are several layers which appear rich in organic material -- and for which radiocarbon dates will presumably be obtained.  It will be interesting to see what comes out of these investigations.

In summary, we have traces of at least two glaciations here, with most of the major erosion and landscape development attributable to the earlier one, and most of the deposition of superficial deposits attributable to the later one.  There is undoubtedly a great deal more to be discovered, and I hope that MPP has some good geomorphologists on board to help him in the task of unravelling what actually went on.

If MPP wants to make use of the above material, he is welcome to do so, as long as he acknowledges the source.

The Rhosyfelin litter

 

Click on the picture to enlarge

This picture of the inner (upper) part of the Rhosyfelin dig 2012 shoes a very steep bank of litter or broken stone accumulated to quite a high level on the rock face, with no clear organization or arrangement of stones.  Entirely natural, as far as I can see.  What is more interesting is the broken stones which we can still see in position ABOVE the cliff, with the turf tumbling down over them.  Most of them are lying flat, rather than being on edge -- as we would expect if they have come down from higher up, moving down and over the little cliff face under the influence of gravity.

This reinforces my view that many of the stones now exposed on the floor of the dig have not been levered from the cliff face but have come down from the crags above. Many of them have simply accumulated as scree -- other stones might have slid down over snowbanks, since this gully is a perfect place for snowbanks to accumulate during periods of cold climate.

About turn on Garn Turne

One of the most interesting things about the evening at Brynberian was the presentation by Colin Richards on the 2012 excavations at Garn Turne, some way away from Rhosyfelin and in the southern Preseli foothills.  The key feature is the massive 80 tonne capstone at the heart of a portal dolmen.  Previously, Colin has maintained the line that the capstone was moved from the rocky crag at the top of the hill by our sturdy ancestors, and indeed his team started to dig into a hollow near the summit which was assumed to be the place from which the stone was taken.  However, when they excavated there, they discovered that it was nothing more than a buried wartime lookout or some such thing, even including a concrete slab.  (I think that's what he said....)  So that was ruled out, and after this year's dig the conclusion is that the huge recumbent stone has simply been used in the place where it was found.  That's a major turnaround in interpretation, and great respect is due to Colin Richards for that......

Two really interesting things have come out of the dig. 

First, that there are TWO dolmens here, in the same place.  The first (a small one) used as a capstone the boulder we can see in the photo immediately to the right of the tree shadow, slap in the middle of the portal to the second -- later -- dolmen which used the 80-tonne capstone.  So there is multiple use here, with at least two generations using the same site.

Second, the huge second capstone has been raised bit by bit, through the use of long levers (wooden poles) and packing stones to hold it up as it was raised laboriously, inch inch, from its original bed.  The grooves can still be seen, in which the ends of the levers were placed.  They were no fools, these fellows, since they used exactly the same technique as I use in my garden when I am trying to shift a 2-tonne erratic boulder which is projecting inconveniently through the ground surface...........

So there we are then.  This time we have a glacial erratic used at the place where it was found, not all that far from its source.  Colin also confirmed what Steve Burrow has said -- that the tradition in Wales was not to move large capstones, but to use them in the places where they have been dumped by ice or else where they occur at natural rock outcrops.  Now what was I saying about that all those months ago.....??

The Rhosyfelin Railway Track

This is exactly where the "rails" are supposed to be.  The big recumbent stone is on the left, and the cliff face is off the photo to the right.  So the slope runs down from right towards left.  Rails?  Sorry chaps, but I see no rails -- just a jumble of broken scree.

Rhosyfelin 2012

I couldn't get over to the dig site yesterday, but thought I'd better zap over early this morning before the hole gets filled in....  met one of the archaeologists there, and managed to have a quick look around.  Here are some of my photos:

This shows the whole dig site -- rock face to the left, rubble and big stone in the centre, and the banks cut into the thick sediments on the right.  We are looking up the slope towards the head of the gully.

This is the rock face, seen from higher up the gully.  You can see from the change in colouring just how much of it has been covered up -- before this dig -- with sediments and vegetation.  The cliff is effectively now twice as high as it appeared originally.

 

This is the "damaged" or "crushed" stone just beyond the downslope edge of the large stone they refer to as an "orthostat".  Yes, it is damaged, but it seems to me that the damage is no more or less than we see on scores of other stones on the site.  Is the damage fresh enough to be attributed to Neolithic quarrying activity, or is it a natural consequence of frost-shattering during one of the periglacial phases to have affected this area?

This is the enigmatic socket that has everybody puzzled.  It's a few feet across.  Did it really hold a large standing stone, or was it a storage pit or something that had another purpose?  MPP is convinced it held a stone for c 4,000 years, and that the stone was finally toppled or removed around 500 AD.  Evidence eagerly awaited...

This is the so-called "activity floor" where traces of charcoal, burnt stone etc were found.  Assumed to be traces of an Iron Age encampment.....

The deep vertical crack in the rock here is said by Richard Bevins to be the sampling point for the most accurate match yet between the Rhosyfelin crag and some (how much?) debitage from Stonehenge.  So the claim is that there is a piece of provenancing here which is accurate to within a metre or two.  I want to see chapter and verse on that, since unless you have a 1m sampling grid over a wide area it is pretty hazardous to make that sort of claim.  The that as it may, this is very skilful provenancing by Rob and Richard.  The problem is that this does not look like a place where even a small boulder has come from, let alone a massive orthostat.  If you look at the whole rock face it is incredibly smooth, and I think it is glaciated.  I think also that the great mass of the debris here has not come from the rock face but from ABOVE it -- I think that glacial and periglacial processes combined have led to a collapse or series of collapses of material that has crashed down from the upper part of the slope where there are still many gorse bushes etc.  Maybe some mountaineering is called for in the winter, when the vegetation has died back a bit.

Well well, this is all getting rather interesting........

An evening in Brynberian

 The 2011 dig -- showing the big stone which has caused more excitement than is really justified, and the litter of smaller broken stones banked up against the rock face.

A photo taken by Linda Norris, showing how much bigger the 2012 dig is, and showing the great bank of rubble and slabs between the big stone and the rock face.

Well, I turned up last evening to the packed village hall in Bynberian to hear the presentations from Colin Richards and Mike PP.  Very jolly fellows, both of them  - and I say that without a hint of sarcasm.  The presentations were interesting and informative -- and they were pretty up-front about everything.  And I refrained from making any comments at all in public, having been exhorted on all sides to be on my best behaviour.  I was very proud of myself.  And that was in spite of the speakers steadfastly refusing even to utter the words "glacial erratics" -- almost as if they might have caused grave offence among the members of the audience.......  Of course, most of the audience turned up hoping to get a jolly good story, and that was what they got -- with the borders between fact and fantasy very blurred indeed.  That having been said, I found that both Colin and Mike were a good deal more circumspect than they were last year in the language that they used.  On this occasion, my blood did not boil.  So maybe we are making a little progress.......

I also visited the site at Rhosyfelin, and had a long chat with Colin, whom I found very straightforward and open. 

First of all, the site.  The dig is now ENORMOUS -- they have extended in all directions, although I don't think they have gone any deeper than last year, since I'm keen to see if there are fluvioglacial gravels (or even till) beneath the slope deposits which they have been investigating.  They have been carefully removing all of the fine material around the broken rock debris that litters the "floor" of the excavation, as seen in the old pic above and in the other pic (from this year) below.

The key features which MPP is using in support of his quarry hypothesis are as follows:

1.  An elongated stone perpendicular to the lower end of the big recumbent stone which has a damaged upper surface.  MPP argued that this damage is the result of other big stones being dragged over it before the current big one was left where it is. My view?  The stone certainly does have a broken upper surface, and it is conceivable that the damage was done by a big stone -- or several --  being dragged across it.  But I'm intrigued by how rounded and moulded it is -- and I am pondering on whether quite a lot of the stones exposed at the bottom of the dig have actually been moulded by over-riding ice.  I was really struck by this moulding when I looked at the dig -- but it has not been commented on by the archaeologists.  Human versus natural?  50:50

2.  The hammer stones and mauls found here and there in the dig.  I haven't examined them myself, and I 'm not sure where they have come from, but a photo was shown purporting to be of one of them insitu, embedded in the midst of a litter of angular stones.  The other archaeologists to whom I spoke said that these stones are fractured and damaged by percussion --  and for the moment I'm prepared to accept that they know what they are talking about.  Not sure what rock types they are made of -- but if they are genuinely foreign, that would strengthen the MPP case.  Human versus natural?  75:25

3.  There is an Iron Age date (around 500 BC?) from charcoal (?) somewhere on the site, which I suppose shows that at that time there were people around here, making fires.  Date obtained in 2011?

4.  The elongated "railway lines" or "sliding stones" shown in the photo in MPP's book, and along which big stones were supposedly slid sideways down the slope from the cliff face.  I couldn't see them last year, and I couldn't see them this year either.  More fantasy than fact? Human versus natural?  20:80

5.  A huge stone pit or socket, reputed to have held a big standing stone held in place with packing stones.  You can glimpse the edge of this pit at the extreme L edge of Linda's photo.  I have to accept that this is real, rather than just an artifact created by the diggers -- but it is quite an anomaly.  Nobody seems to know what to make of it.  It's a very strange place for people to have put up a standing stone -- down near the floor of a wooded valley, close to a rocky crag.  MPP thinks that a big standing stone or monolith was in position here until the Iron Age, when it was removed or smashed up.  No trace of it today -- unless the stones found in the pit are the remnants of it.  Human versus natural?  90:10

6.  A strange "activity surface" in the flattish area behind the people in Linda's photo.  MPP seemed to suggest that this was another Iron Age feature -- with flints, chips, flakes, charcoal and burnt stone in a quite extensive spread of debris.  Then, after 500 AD, the site was covered with hillwash and slope deposits.  So -- traces of human activity, certainly -- but quite the wrong age to be used in support of the "Neolithic Quarry" hypothesis.  MPP argues, of course, that the standing stone and this evidence of Iron Age occupation (even if for a very short time, in a seasonal winter camp, maybe) shows that the site was revered as a quarry site from which sacred stones had been taken long ago ---- and hence that there must have been USE of this site over many thousands of years.   Hmmm -- that sounds pretty fantastical to me -- and I wouldn't mind having a bit of evidence to support the idea.

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

That seems to be the essence of the "case for the Quarry" -- although the geology evidence is jumbled up in the argument too.  Richard Bevins was at the lecture, and I had a good chat with him about provenancing etc.  I'll cover that in another post.  But for the moment I'll say that the geological evidence is neutral -- it is nothing more and nothing less than an interesting piece of geological detective work, and it does nothing to support the Quarry Hypothesis.

In summary, there is clear evidence of human occupation of this site -- I have no wish to deny that.  But whether there was NEOLITHIC occupation is quite another matter.  There do not as yet seem to be any radiocarbon dates to support occupation around 3,500 BC -- which is the date which MPP now speaks of as the date for the "first known presence of bluestones in the Stonehenge area."  That's a very long time ago -- 5,500 years ago.  Is it really likely that Iron Age tribes in this area would have continued to revere a site first used 4,000 years earlier?

Far more questions than answers.  Currently, my thinking is that this site has nothing whatsoever to do with the human transport of big stones to Stonehenge -- but that it might have been used intermittently for the fabrication of implements, given the lovely sharp edges which this rhyolite gives.  so in that sense, it might have been a quarry or a factory.  Later on, some Iron Age people used this sheltered site against a craggy rock face in a wooded valley as an encampment -- maybe over the winter months.

Finally, a word about artificial significance.  Archaeologists don't think about it often enough.  We could also call it sampling bias.   I am pretty convinced that MPP and his colleagues have invested this site with significance because they have decided in advance that it is a Neolithic quarry site.  It is perfectly reasonable to think that if they had visited almost any sheltered craggy site in a north Pembrokeshire valley (and there are many of them) and subjected that site to this level of scrutiny, they would have found virtually the same assortment of features -- including a litter of large blocks and slabs, and even traces of temporary encampments in the Iron Age.

To be continued......