The Kokelaar Guide to erratic pebbles

The info below is extracted from the following excellent resource: 

https://kokelaargower.com/towards-stonehenge-the-anglian-glaciation-of-gower/

The pebbles illustrated below have all come from Gower raised beaches -- derived from many different places.  I'm particularly struck by the Ramsey Island connection -- as flagged up here by somebody who knows the igneous rocks of that island particularly well.  Some of these look very familiar -- I have seen them in abundance on the Pembrokeshire beaches, and also on Flat Holm in the middle of the Severn Estuary.

Silicic volcanic and shallow-intrusive rocks -- probably mostly from Ramsey Island

Mafic intrusive and extrusive rocks -- mostly from NW Pembrokeshire and maybe Skomer island

Diverse igneous erratics -- some from North Pembrokshire coast, Skomer and possibly Scotland

Silicic and intermediate intrusive rocks -- from Ailsa Craig and other distant sources

For further details on the provenances and rock types, please consult Peter's blog -- link as above.

The Contentious Reach

 As mentioned in a previous post, I really like an idea put forward by Prof Peter Kokelaar in his blog -- namely the idea of the "contentious reach".  This is the ill-defined area to the east of the Bristol Channel coasts of Cornwall, Devon and Somerset in which the evidence of Quaternary environmental change is quite difficult to interpret.  It is also the area which is now crucial to the debate about the transport of the bluestones that are present in the stone setting of Stonehenge.  I have discussed the evidence from this area on many occasions in this blog, for example in this post:

https://brian-mountainman.blogspot.com/2024/08/towards-late-wolstonian-mis-6-ice-limit.html

Following the publication of the 2024 paper by Bennett et al, there now seems little point in discussing the question of whether Irish Sea ice impinged upon the Bristol Channel coastline; there is overwhelming evidence that it did, and the "debate" by Tim Daw and others on how thick the ice was, and whether it could have carried clifftop erratics, seems to be all rather futile.  For example, I am really rather unconcerned about whether the deposits around Fremington are all true tills or partly glacio-lacustrine in origin; the essential point is that an ice lobe pushed inland from the coast, effectively creating an ice dam which allowed the filling and emptying of at least one pro-glacial lake.  Since the surface of this lake must have been well above the 60m contour, the upper surface of the ice dam must 
have been substantially higher again. Did it lie at +80m? Or perhaps at +100m? Who cares.........

Bennett, J. A., Cullingford, R. A., Gibbard, P. L., Hughes, P. D., & Murton, J. B. (2024). The Quaternary Geology of Devon. Proceedings of the Ussher Society, 15, 84-130.
https://ussher.org.uk/wp- content/uploads/benettetal1584130v2.pdf

So let's accept that the edge of the Irish Sea Ice Stream, on at least one occasion, more or less coincided with the cliffline of the western coasts of Cornwall, Devon and Somerset. This is a perfectly straightforward scenario, given that the cliffline is a substantial natural barrier and given that on at least one occasion the Scilly Islands were covered with glacier ice:

https://www.researchgate.net/publication/328413421_Evidence_for_extensive_ice_cover_on_the_Isles_of_Scilly 

https://brian-mountainman.blogspot.com/2019/03/scourse-versus-john-rather-scilly-spat.html

Let's for the moment forget about the debate surrounding the extent of Late Devensian (LGM) Irish Sea Ice Stream ice.......  and let's forget the claim (based on zero evidence) that the large erratics found in places on the coast have been ice-rafted at times of high sea level.

So what do we know about the Quaternary record inside the "contentious reach"?  Well, the evidence seems pretty convincing that there were at times small local ice caps on Dartmoor, Exmoor and Bodmin Moor, and possibly small localised snow domes on some of the smaller hill masses.  Candidates would be the Quantocks, Brendon Hills and Blackdown Hills. Stephan Harrison has suggested that there were a number of small "plateau icefields" which supported thin and more or less immobile ice in a landscape of extensive snowfields and permafrost.

https://dartmoorsociety.com/pastevent/the-glaciation-of-dartmoor/#:~:text=The%20Irish%20ice%20cap%20did,Southwest%20England%20was%20not%20glaciated.  

The Mendips might be looked on as a special case -- and I have examined (in previous blog posts) some of the signs that suggest dramatic meltwater flow and a periodic ice cover.

https://brian-mountainman.blogspot.com/2018/10/on-significance-of-mendip-for.html

Then we come to the position of an ice edge coinciding with the Somerset coast of today. It is highly unlikely that the ice edge ever sat in this position for an extended period, since during glacial episodes the coastline was removed far to the west, somewhere near the -120m seabed contour.  Dynamic or active ice will always seek to fill pre-existingt depressions in preference to seeking to surmount inconvenient obstacles. I will hazard a guess that no glaciologist would argue with the point that if glacier ice reached Kenn, Gordano Valley and other locations near Bristol up to 25 km inland from the coast, it must also have filled the Somerset Levels depression.  We know that a diamicton widely interpreted as a till exists at Greylake, c 15 km inland of the present coast, and it is in my view inevitable that ancient tills will in due course be discovered beneath thick peat and other sediments in many other west Somerset locations.

In other words, the famous Gilbertson and Hawkins map of 1978 is not far wide of the mark..........

  

What about areas to the north -- around Oxford and the Thames valley?  Well, glacial clay deposits have been identified in the "wooded plateau" area of the Chilterns: isolated plateau areas to the north-west of the Chilterns Escarpment around Brightwell, Grove and Oakley Wood.  

https://owls.oxfordshire.gov.uk/wps/wcm/connect/occ/OWLS/Home/Oxfordshire+Landscape+Types/Wooded+Plateau/

The "plateau drift" or "northern drift" also occurs quite widely on old hill summits and plateau remnants to the NW of Oxford, in the Evenlode Valley, and also in isolated patches to the south of the city and to the south of the Thames river.  The evidence is disputed, but I recall being taken on a field trip by Dr Kenneth Sandford way back in the 1960's -- on which I was very convinced that the "plateau drift" is (at least in part) a genuine in situ glacial deposit which can only have been dumped by ice flowing down from the north or north-west.  Others interpret the plateau drift as a pre-Anglian fluvial deposit extending as far south as southern Berkshire and marking a very early course of the River Thames.  In a comprehensive study of the "plateau drift" in 1980, Shotton et al concluded that it is a complex deposit of great age, including reworked and fluvially redistributed gravels, some of which have been "decalcified" and subjected to mechanical and chemical alteration over many millennia.  But crucially they determined that some of the deposits analysed could not be explained other than by glaciation of the Oxford region.

https://www.researchgate.net/publication/247604991_Cromerian_Interglacial_Deposits_at_Sugworth_Near_Oxford_England_and_Their_Relation_to_the_Plateau_Drift_of_the_Cotswolds_and_the_Terrace_Sequence_of_the_Upper_and_Middle_Thames#:~:text=are%20drawn:-,1.,Terrace).

In their consideration of the "Ardleigh erratic" found in river gravels not far from Colchester, Rose et al (2010) were in no doubt that there was at least one glaciation of the upper Thames catchment in the region of the Cotswold Hills.  The glaciation was associated with the Bruern Till, and must have involved ice that originated in North Wales.  Bridgland and others who have also studied the Upper Thames terraces have also agreed that there are many locations where the high erratic content in the gravels indicates derivation from destroyed or undiscovered early glacial till deposits -- in other words, from the "northern drift" or "plateau drift"..........

https://nora.nerc.ac.uk/id/eprint/11416/1/Ardleigh.pdf

https://brian-mountainman.blogspot.com/2022/02/a-very-erratic-essex-erratic.html

If we wish, therefore, to take the idea of the "contentious reach" seriously, we would include within it the Upper Thames Basin, the Cotswolds, the Mendips, the Severn Esuary and lower Severn Valley, the Newport - Gloucester area, the  chalk downs of Wiltshire and Salisbury Plain, and much of Somerset, Devon and Cornwall.

Based on the Gibson and Gibbard map, I have designated the area within the dashed blue line as "the Contentious Reach"...............

All in all, it is certain that there are many incontrovertible traces of glaciation within the Contentious Reach.  The size of this disputed area will inevitably shrink as more and more evidence is assembled.

Updated marine isotope stages (MIS sequence)

In some of the recent articles I have been reading I have seen a few anomalies in the use of the MIS labels.  This makes things somewhat confusing.  So I asked the Google AI search facility for an updated listing of the MIS sequence as used in recent publications,  with British labels attached.  Worth sharing.  Here it is.

I am particularly intrigued by MIS 10 -- a glacial episode which might be represented in the South Midlands.   But it seems to have no name.   More on this in due course........

Erratic paradise

 

One of the great joys of our holidays in the Stockholm Archipelago is the exploration of small islands and skerries by kayak, discovering erratic conglomerations like the one above.  In places there are exposed, smoothed and striated rock outcrops visible along the shoreline, and in places the shoreline is covered with accumulations of erratics that have come from multiple locations.  There are very few morainic constructional features that one might refer to as terminal or recessional moraines.  The litter is everywhere -- made very visible and prominent because the whole landscape is "washed" as a result of ongoing isostatic uplift or recovery.  Many of the low skerries have literally emerged from the sea within the last few centuries, as evideenced by intermittent raised shorelines of cobbles and gravels.

This whole archipelago was deeply submerged beneath the ice of the Scandinavian Ice Sheet on several occasions during the Quaternary.  There was a great deal of areal scouring and very little erosion by identifiable ice streams -- although it is clear that basal ice did move more rapidly in places in response to topographic irregularities on the bed.  For example, the deep channels between the islands of Blidö and Yxlan must have enouraged streaming flow and must have led to localised variations in the direction of basal ice flow -- which was overall directly north to south.

Satellite image of part of the Stockhgolm Archipelago.  Ice movement here was north to south, but on a small scale there were variations in ice flow directiuons influenced by old valleys, hills and other topographic details

In all of my coastal observations I have never been able to trace a true earratic train for more than a few tens of metres.  The abiding impression is that every boulder and cobble has a unique history -- sometimes moving, sometimes stuck, sometimes travelling directly southwards and sometimes in zigzag fashion dependent on topographic controls and oscillations in basal ice temperatires and flow characteristics.  And while, during any given glaciation, there must have been entrainment of fresh blocks on the glacier bed, many blocks such as those in the photo above must have been moved, embedded, and moved again over a series of glacial episodes.  

It seems to me that this process of entrainment and debris recycling goes on regardless of where the glacier snout is positioned.  This is an important point, since it means that in any given glaciation of the Bristol Channel old erratics can be stuck or dumped virtually anywhere, and new erratics can be entrained almost anywhere, right up to the ice edge as long as the ice continues to be active.  There are a number of different mechanisms.  For further details, see the standard texts............

In response to this constant process of entrainment, dumping, recycling and renewal, the majority of erratics on any ice sheet bed at any given time will be rather local, some will have travelled modest distances (tens of kilometres) and a few will be far-travelled (maybe hundreds of km).

This generalisation confirms what I have observed in the Quaternary sites around the Pembrokeshire coast.  It's rather futile to do a numerical / statistical analysis on this, because local circumstances vary so much, but in till (or on storm beaches such as Abermawr, where almost everything is derived from destroyed glacial deposits) MOST of the clasts are local, SOME of the clasts have come from more distant sources (such as Ramsey Island), and A FEW have travelled really long distances (such as Ailsa Craig).  

Newgale storm beach, where the great majority of stones have come from destroyed glacial deposits during the inexorable advance of the sea across the land surface.

As for the shapes of boulders and smaller stones in these three categories, they are not greatly dependent upon distance travelled.  A rockfall boulder deposited on a glacier surface will retain its angular edges for maybe hundreds of kilometres so long as it is not incorporated into the glacier mass and subjected to abrasional and other processes.  In contrast, a boulder entrained near a glacier snout can be heaily abraded if it is stuck on the glacier bed for decades or centuries with ice flowing over and around it.  Great care is needed in the interpretation of ALL clasts, including sharp-edges boulders and those that are heavily abraded and striated.........

More contributions to the bluestone transport debate

I have been looking at Prof Peter Kokelaar's blog, and  have discovered there a great deal of new evidence relating in particular to his work in Gower and north Pembrokeshire.  These three blog posts are particularly useful:

https://kokelaargower.com/stonehenge/

https://kokelaargower.com/towards-stonehenge-the-anglian-glaciation-of-gower/

https://kokelaargower.com/gowers-famous-patella-beach/

Peter's work concentrates in particular on the effects of the Anglian Glaciation.  I don't agree with everything he says, but we can agree to differ until more conclusive evidence on glacial episode dating comes to hand.  But it's gratifying to know that in his work -- quite independent of mine -- he has come to broadly the same conclusions.  He suggests that much of the narrative developed by MPP, Ixer and Bevins about quarries, lost circles and so forth is unreliable, and that the glacial transport theory is far more likely to be correct than the human transport theory which suffers from a complete lack of supporting evidence.  He is also very sceptical about the proposal that the Altar Stone has come from the far NE of Scotland -- basing his views on zircon work which will no doubt be elaborated in future publications.

I like his work on Stonehenge bluestone shapes (Fig 3 in the Stonehenge article) but note that he shows some of the bluestone monoliths as pillars, whereas I have classified them as slabs.  That is a small point.  I look forward to further work on this topic.

And I also like his idea of the "contentious reach" -- an ill-defined area between the Somerset coast and Stonehenge, where the evidence is very subtle and difficult to interpret.  It's shown on his map which I reproduce at the head of this post.

Quote:

...........In the human-transport view, Stonehenge would be the only known ritual site where numerous (at least 43) pieces of non-local and not especially remarkable material, up to 3.5 tonnes in weight, were carried several hundreds of kilometres (overland some 300 km / 186 mi and by water 435 km / 270 mi). There is no known field record of this anywhere. We do know, however, that prominent, weather-resisting stones lying around within a largish area – perhaps 10s of kilometres away – definitely were commonly collected, brought together and carefully erected. Some of the Stonehenge sarsen stones, a few over 30 tonnes, are thought to have been collected from about 24 km away (Field et al. 2015; Harding et al. 2024; Daw 2025). In the Preseli area spotted dolerite stones were only used where they occurred locally, near to where they are found today, and there exists no evidence of them being especially revered. Motivation for the “stupendous feat” in human transport has always been a problematic weakness in the case, earlier attributing fantastic reasons like magical powers or sonic properties to the stones, or later mistakenly claiming reverence for them in sites of previous circles that then acted as sources for removal and transport (e.g., Parker Pearson et al. 2021). Fantastic claims, including inference of active quarrying to produce the stones at rock outcrops that are actually typical of natural jointing, weathering and collapse, are now, with sensible geology and geomorphology, and with robust geochemical evidence, thoroughly debunked. So, no quarries and no uprooting of former monuments (Bevins et al. 2022; John et al. 2015; John 2025).

Quote:

Craig Rhosyfelin also features as a bluestone megalith quarry, in this case of rhyolite (foliated rhyolitic tuff), despite there being no known megaliths from there, just a buried stump and a few lumps and many chips recovered at Stonehenge. The provenancing is robust, for its geochemistry and rock texture, but again, despite extensive and time-consuming excavations, no quarrying could be established. Despite objections made regarding the ‘quarries’ (e.g., John et al. 2015), there was no retraction while the focus shifted to removal and transport to Stonehenge of pre-existing monuments (Parker Pearson et al. 2021). In the now infamous BBC ‘Stonehenge: The Lost Circle Revealed’ (2021) a long search eventually ‘found’ the site of a dismantled circle at Waun Mawn that was claimed to have sourced Stonehenge stones. This was proved for viewers by the imprint of a removed stone at Waun Mawn that fitted a stone at Stonehenge “like a key in a lock”, with computer-graphic confirmation. The stone that was supposed to fit is Stone 62 (see Figs 1 and 2). The interview based on this ‘clinching discovery’ concerned a revolutionary new view of collaboration between ancient societies. The trouble is, however, that robust data show that the Waun Mawn stones came from a local source (Bevins et al. 2022) unlike anything at Stonehenge, while Stone 62 came from the eastern Preseli hills not far from other known natural sources. So the whole programme, with its intense and dramatic revelations of quarrying and removal from a former stone circle, proved to be spectacularly wrong. One might say that hindsight is a wonderful thing, but contemporary expert advice was always available and ignored, and the subsequent media show on what is known to be a topic of wide interest was an information disaster.

And on the "cow tooth" findings:

The claim that the cow-tooth findings add to confirmation of the “theory” that cattle were involved in transport of the megaliths is udderly ridiculous. (BJ -- I wish I had thought of that one!) Apart from confusing theory and hypothesis in this media hype, the unjustified claims were disturbing as they came from the Press Office of the British Geological Survey; no sane geologist would support them. Actually, the original scientific report of the cow-tooth findings, in contrast to the hype, was quite reserved, acknowledging limitations to interpretations that should be borne in mind. What is it then, really, that causes decent science to be so compromised in the media? There certainly is cavalier ignorance on the part of media producers, whose driver seems to be promotion of viewing figures or sales…

I'll return to these blog posts on another occasion when I have had a chance to read them more carefully.  As we see in the above quotes, in quite a few places in his posts, Peter does not mince his words.........

Prof Peter Kokelaar, who was George Herdman Professor of Geology in Liverpool University

The "no erratics" mantra is disingenuous and unscientific

One of the Berwick St James bluestone erratics -- limestone, but no less respectable and interesting

than the Stonehenge igneous bluestones

 "There are no erratics on Salisbury Plain, and therefore the glacial transport theory can be dismissed."  How many times have we read that, or something very like it, in archaeological tomes and "learned" articles?  Too many times to count.  Well, it is high time to call this out as utter tosh, and to insist that the people who think of themselves as Stonehenge experts started to demonstrate greater integrity in their work.

This is a typical statement (regarding Silbury Hill) from Ixer, Bevins and Pollard:  "The finding of five samples of Stonehenge debitage, one in a secure Neolithic context, supports the suggestion that all were brought to Silbury in prehistoric times and can no longer be dismissed as extraneous."  What on earth does that mean?  That because one sample is in a "secure Neolithic context" they can assume that the others are equally secure or relevant?  And that those that do not have secure archaeological contexts can be "dismissed" as having no relevance at all?  That is patently absurd --  the fragments might have huge significance for the debate surrounding bluestone transport.  And on what grounds do they refer to the fragments as "Stonehenge debitage"?  That is completely unscientific.

Over and again, in the literature, inconvenient bluestone fragments are dismissed as "adventitious" on the basis that somebody or other, in historic times, might have carried them in from somewhere else and dropped them or thrown them out into the landscape.  They might even have carried them into an excavation site and left them there, buried in "debitage"...........

Following on from a comment by Tony the other day, let's look at the word "adventitious".  It means "accidental" or  "coming from an outside source and not being an essential part of the context".  Another definition: "appearing in other than the usual or normal place."  In other words, something eccentric or erratic.  So there we are then -- an "adventitious find" of a foreign stone (of any size) is an erratic erratic.

Here are a few more definitions:  unexpected, unplanned, untimely, inconceivable, inadvertent, unwelcome.  So there are value judgments in there as well -- the sense, very often when the word is used, is that it would make the finder's life very much simpler if the "adventitious find" had not been found at all!  There we come to the crux of the matter.  Large or small finds of bluestones on Salisbury Plain, in places where they should not exist (according to your belief system) can be dealt with by dismissing them or dominishing their possible importance.  Confirmation bias rules the day, as it has done at Stonehenge for decades, as the establishment narrative is repeated or elaborated over and again, ad infinitum.

An erratic stone, as I have often tried to explain very patriently, is a stone (of any size) that is found in a location remote from its place of origin. On that basis I am not entirely sure that the sarsen monoliths and smaller sarsen stones at Stonehenge are erratics at all -- since they may simply have been "let down"  from a pre-existing sediment cover that has otherwise been eroded away.  We'll leave the sarsens to one side for now.  

As for the other erratics, there are countless examples all over Salisbury Plain and the chalk downs.  That is not disputed by anybody.  The Berwick St James limestone monoliths are erratics.  The Stonehenge bluestone monoliths are erratics.  The Newall Boulder and the Meaden Cobble are erratics.  The Boles Barrow bluestone is an erratic.   The bluestone fragments found in the Cursus are erratics. The spotted dolerite stone found near Lake is an erratic.  The oolitic limestone "filler stones" at West Kennet are erratics.  The Stonehenge non-sarsen packing stones are erratics.  The West Kennet grus comes from at least one granidiorite erratic.  And so on.  And so on.

Another point needs to be made.  Traditionally the members of the Stonehenge establishment have pretended that there is a difference between the bluestones and the non-bluestones.  According to their definition, the bluestones have all come from West Wales, and recently Ixer and Bevins have muddied the waters further by promoting the idea that the Altar Stone is not a bluestone because it might have come from Scotland.  Similarly, the abundant sandstone and limestone clasts on Salisbury Plain that have come from sedimentary outcrops on the fringes of the chalk terrain are quietly forgotten about on the basis that they are not bluestones and because (so they say) they have clearly been carried in by human beings.   Sorry, but the circular reasoning is all too apparent...........  And it is somewhat intriguing that the majority of them seem to have come from the west and south-west -- just as we might expect if ice was involved in their transport.

So it is perfectly feasible that many if not all of the limestone and sandstone fragments and larger clasts that occur on Salisbury Plain, and which have apparently come from sites within twenty or thirty miles, have been entrained and transported by glacier ice.  At any rate, I propose that all of these non-sarsen stones should be referred to as "bluestones".  That would make life much simpler for everybody.

EVERY exotic stone on Salisbury Plain and on the adjacent downs is of great potential significance, and MUST be accepted as an erratic.  It's high time that the archaeologists and geologists who express their views about prehistoric events started to show some honesty and responsibility in this matter.  

Once the erratics are accepted and labelled for what they are, and are all accepted as valid bluestones, we can move on and discuss, in an unbiased fashion, how they might have travelled from their assorted places of origin, both near and far.

 

 

More limestone erratic blocks in Wiltshire

 The two Berwick St James stones, now on either side of a roadway

A reminder that the "Meaden Cobble" is not the only piece of limestone found on the downs or Salisbury Plain.  There are many pieces assumed to have been used as packing stones at Stonehenge itself -- not sure whether anybody has actually counted them........  

But the most intruguing occurrences are the Berwick St James stones -- which may originally have been one larger slab, used as a footbridge across a local stream.   There is no archaeological context, but for years it was assumed that these stones were related to the Altar Stone at Stonehenge.  More recently it has been discovered that there is no geological or petrographic link, and that the two stones in question are limestone, not sandstone. They are referred to as peloidal packstone and packstone/grainstone.   The stones have a somewhat unusual knobbly or lumpy surface.  This specific "impure" limestone is rare in the Lower Jurassic period; there may be a source from the Middle or Upper Jurassic.  The nearest feasible natural source for this rock type is near Tisbury, approximately 22 km (14 miles) southwest of the Stonehenge area.

See Thorpe and Williams-Thorpe, 1992.

The stones are erratics, and they have clearly not been carried in to this site as building stones or road metal!  Maybe they were once (as a single slab) used as a standing stone somewhere in the vicinity?  The heavily pitted surface suggests very long exposure to the elements and to loss of mass due to solution........

Here is a 2024 somewhat speculative comment from Andrew Collins on Facebook:

https://www.blogger.com/blog/post/edit/1228690739485734684/261207925045772628

Great new video on the hunt for the second Altar Stone at Stonehenge with Hugh Newman and myself. All the evidence seems to point right now to two standing stones, partially buried, at a place called Berwick St James just a couple of miles west of Stonehenge. These stones are strongly suspected to have been fragments of a single huge megalith 15 feet in length, matching very well the existing Altar Stone. Critics of the Berwick St James stones being the second Altar Stone point out it is made of limestone and no limestone was ever used at Stonehenge. Thus the Berwick St James stones are a red herring. However, working with Stonehenge expert Simon Banton we have uncovered incredible new evidence that limestone was indeed used at Stonehenge. More than this various fragments of limestone were found in the exact vicinity of the stone hole now thought to have contained Altar Stone 2. All is revealed in a new article being prepared right now.

The taller of the two Berwick St James stones -- note the pitted and lumpy surface

 Further developments awaited -- suffice to say, for the moment, that the idea of a second Altar Stone is not universally accepted...... 

https://www.youtube.com/watch?v=WUWB8lySAu4&t=32s

Then there are the Shelving Stones, near Avebury. They were mentioned some years ago by Pete Glastonbury.  Most of the stones are sarsens, but there is also oolitic limestone at the site.  (I haven't been able to find a photo).    Current archaeological theory -- which may of course be completely wrong -- suggests that this limestone was deliberately transported 10–12 miles from distant outcrops.  The oolitic Limestone was identified by Mike Pitts and later confirmed by Jim Gunter.