Some of the ideas discussed in this blog are published in my new book called "The Stonehenge Bluestones" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Saturday, 7 December 2019

Kealkill megalithic complex, Ireland

Ah -- what a fabulous image.  It was featured on Austin Kinsley's Facebook page -- worth sharing.  It shows the Kealkill megalithic complex near Bantry Bay, in Ireland.

Stonehenge 1944

Fabulous image from Austin Kinsley's Facebook page.  Many thanks. It's a highly unusual and fascinating photo taken in 1944 as a trial, when various techniques of aerial photography were being tried out.  Apparently when this was taken the strobe lighting came from an aircraft flying overhead at altitude of 1500 feet.  Very moody......

Thursday, 5 December 2019

Stonehenge - more on the Devonian (?) sandstones

The petrographic differences between the four studies samples.  Note that the old "type section 277" has just been examined visually, and that the other three -- including the new type section -- have been subjected to QEMSCAN analysis.  That may have resulted in analytical error -- but the authors are confident that the differences are significant and that they will withstand scrutiny.  

I have been looking again at the 2019 paper by Ixer et al on the carbonate-cemented micaceous sandstone samples collected over the years at Stonehenge:

Alternative Altar Stones? Carbonate-cemented micaceous sandstones from the Stonehenge Landscape
by Rob Ixer, Richard Bevins, Peter Turner, Matthew Power and Duncan Pirrie
Wiltshire Archaeological & Natural History Magazine, vol. 112 (2019), pp. 1–13

The six-tonne recumbent Altar Stone is perhaps the most enigmatic of all the Stonehenge bluestones, differing markedly from the others in size, tonnage, lithology and origin. It has therefore had more than its fair share of speculation on all of these aspects and many questions remain: was it always recumbent, was it a singleton or half a twin, where did it come from? Clearly it is not from the Preseli Hills hence the debate as to its geographical origins for over a century. However, any provenancing of the Altar Stone must rely on a detailed and accurate lithological and petrographical description. New descriptions of material labelled ‘Altar Stone’ held in museum collections and a re-evaluation of suggested Altar Stone debitage using automated scanning electron microscopy and linked energy dispersive analysis using QEMSCAN technology suggests that modiļ¬cation of the published petrographical descriptions is needed. A new ‘typical Altar Stone’ description is provided including the presence of early cementing barite and a better characterisation of the clay content. These new data should continue to narrow the search for the geographical origin of the Altar Stone, one that is expected to be at the eastern end of the Senni Formation outcrop, an outcrop that reaches as far east as Abergavenny in the Welsh Marches.

The real significance of this paper is that having studies assorted thin sections (only 4 were suitable for comparative analysis) the authors now feel that the famous thin section 277 may NOT have come from the Altar Stone at all, and that thin section SH18-196 should now be taken as the "type section" for it.  The reason is that the petrography of sample 277 is out on a limb, with various striking differences with samples FN593, HM13-3y/1 and SH18-196.  Those three have close similarities -- close enough in the view of the authors to have come from the same stone.  

What this means is that the carbonate-cemented micaceous sandstones have come from at least two different locations -- probably within the Devonian outcrops of south and west Wales.

There are a further 8 samples of similar sandstones which have not been analysed in this study, and no matter what the geologists may say, there is always a possibility that at least some of these have come from additional sites.  

Note that these are all different from the Lower Palaeozoic sandstones which have just been studied for this paper:

‘No provenance is better than wrong provenance’: Milford Haven and the Stonehenge sandstones,  by Rob A. Ixer, Richard E. Bevins, Duncan Pirrie, Peter Turner and Matthew Power.
Wiltshire Archaeological and Natural History Magazine 113, 20220, pp 1-15.

See also:

Wind direction and landscape change

This is a Bing satellite image and accompanying map to the same scale -- from the wonderful "side by side" web site created by the National Library of Scotland.

This is part of the main upland ride in the Brecon Beacons -- click to enlarge.

You can see here what a profound effect orientation and wind direction have on landscape change during the ice age.  Notice that the main cwms or cirques are oriented broadly NE.  The group of cirques and small glacial troughs in the NE quadrant of the photo were formed because this was the lee side of a ridge, where snow could accumulate and get converted into firn and then glacier ice, during the cold phases of the Ice Age when prevailing winds came from the W and SW.   The long escarpment running from top left to bottom right has been fashioned in a similar way, with a number of small cirques coalescing on the downwind flank of the upland ridge. 

In contrast, look at the valleys in the SW quadrant of the image -- these are "normal" river valleys with no trace of cirque formation.  In the Ice Age most drifting snow was blown up over the ridge to accumulate on the lee (shady) side, leaving the sunny flank largely unaffected. 

Here is another example, showing the Bacons landscape some way to the west, around the famous lakes of Llynyfan Fach and Llynyfan Fawr.   Here the coalescing cirques have a slightly different alignment -- there is a scarp face oriented NNW, but the cwm occupied by Llynyfan Fach is oriented NE, like most of the other cwms in the Beacons.  The scarp alignment may have something to do with the pre-glacial topography.  But note the long river valleys to the south, apparently unaffected by ice action.


The "upland glaciation" of this mountainous region must have occurred intermittently right through the Ice Age.  At other times the mountains were completely ice-free, and at the peak of each glacial episode the whole landscape hereabouts was deeply submerged by the ice of the Welsh Ice Cap.

Mega Megaliths

There seems to be a growing interest at the moment in the biggest standing stones, where they are located and what they are made from.  The one above is named Llwyn-y-Fedwen,  just across the River Usk from the village of Llangynidr; it's a huge piece of sandstone, very battered and weathered, presumably found locally as a glacial erratic.  The hammer measures 30 cm.

Above are two photos of a stone named Maen Dic which is about 500 yards south-west of the village of Battle (about 2.5 miles north-west of Brecon).  Made of Old Red Sandstone?

It seems that these large stones form a cluster in the Brecon, Ystradfellte, and Crickhowell area, the majority of which are very large.  Weight estimates c 5 - 8 tonnes?

Above is Maen Llia (OS grid reference SN924191).  Standing just 60m off the minor road between the Senni valley and Ystradfellte, this impressive stone is relatively easy to visit.  Made from a massive sandstone block which stands 3.7m high, the task of moving and erecting it must have been a huge challenge, especially as it is likely that a quarter to a third of the whole stone is below ground.

Cwrt-y-Gollen (The Growing Stone) in Powys -- grid red:  SO23241686.  This is a magnificent slender pillar c 4.e m high. 

Maen Bredwan, near Neath. Grid ref: SS724995.  It is also called Carreg Bica.   This one, in a very exposed position, is reputed to be 4.3m tall.  According to legend, this stone goes down to the Neath River for a drink once a year, on Easter Sunday morning.  So there we are then.

Maen Madoc standing stone, Powys.  OS grid reference SN918157.  At almost 2.7m in height, this imposing stone (pictured right) stands high on the moors alongside the Roman road, Sarn Helen.
The Latin inscription, DERVACUS FILIUS JUSTI IC JACIT translates as Dervacus, son of Justus, lies here. Dervacus was a sixth century Roman name.  Although widely recognised as a Roman memorial stone, it was probably erected in Bronze Age times, and just came in handy.......... 

Parc y Meirw, near Llanychaer, North Pembrokeshire -- the biggest of the remaining standing stones, c 3m high.  This is part of a famous stone row, now incorporated into a hedge.  The field is named "the field of the dead" because a famous battle was fought here some time in the early Middle Ages.  There is also a "Ladi Wen" -- a white lady -- haunting the field.  


Monday, 2 December 2019

Rotational slump at Red Cliff, Marloes

Can't resist sharing this, since I know that many of our followers like a bit of geomorphology now and again. 

 Here is the coastguard photo of the rotational slump at Red Cliff, Marloes, on the west coast of Pembrokeshire --SM 788071 to SM 790069. A classic of its kind!  This illustrates how coastlines evolve -- with slow and incremental change maybe for centuries or millennia, and every now and then a catastrophic and instantaneous change of vast proportions, triggered by over-sturation of sediments on a slope, or an earth tremor, or an extreme storm event.

The landslide occurred around 21st November. Luckily nobody was hurt.  Must get over there to have a look........

Saturday, 30 November 2019

New paper on the Stonehenge sandstones: significant support for the glacial transport hypothesis

First of all, let's remind ourselves of the current glacial transport hypothesis:  The non-sarsen boulders, slabs, pillars, stumps, stones and "debitage" found in the Stonehenge area come from an assemblage of glacial erratics transported from West and South Wales towards Salisbury Plain by a powerful ice stream, and were later discovered and exploited by the builders of the stone monument.

Now, to the latest paper by Ixer, Bevins, Pirie, Turner and Power, and published in the Wiltshire Archaeological and Natural History Magazine with a 2020 date.    Here are the details:

‘No provenance is better than wrong provenance’: Milford Haven and the Stonehenge sandstones

by Rob A. Ixer, Richard E. Bevins, Duncan Pirrie, Peter Turner and Matthew Power.
Wiltshire Archaeological and Natural History Magazine 113, 20220, pp 1-15.


For over 70 years there has been confusion within the archaeological literature between the Stonehenge ‘Old Red Sandstone’ Altar Stone, the Stonehenge Ordovician-Silurian Lower Palaeozoic Sandstone debitage, and the previously postulated source rocks, the Old Red Sandstone (Devonian) Cosheston Group sandstones. However, petrographic data show that all three are very different lithologies with separate geographical origins. The Altar Stone is most likely to be from eastern Wales and the Lower Palaeozoic Sandstone from west or central Wales, north and east of the Mynydd Preseli; neither of these two Stonehenge-related sandstones is from Mill Bay, Milford Haven as has been suggested. The revised provenance determinations do not support the theory that the Stonehenge bluestones were shipped over sea from the Milford Haven area along the Bristol Channel.

This is a real curate's egg of a paper, containing some meticulous and interesting research, summarising a great deal of material already published, but demonstrating a singular lack of awareness of earth surface processes. It's also very convoluted,  and much more elaborate than it needed to be.  Like a number of other papers from Ixer, Bevins and others on the subject of the bluestones, I cannot imagine that there was even a cursory peer review process prior to publication.  If the Editor had asked me to look at this in its manuscript stage, I would willingly have given him quite a lot of help........ 

However, here it is in print, and in spite of its glaring defects as a scientific paper I have to say that I am rather delighted to see it, because it provides substantial evidence for the glacial transport of the Stonehenge bluestones.

Relevant sandstone outcrops investigated by the authors

In essence, the paper homes in on the Altar Stone (assumed to be Devonian) and the Lower Palaeozoic debitage in the Stonehenge landscape, and the question of whether any or all of the samples analysed actually came from the Cosheston Sandstones outcropping on the shore of Mill Bay. The research is framed as being necessary in order to decide whether the bluestones at Stonehenge were moved by sea or overland;  this is a completely ludicrous piece of research justification since all it does is to demonstrate the tunnel vision of the authors.  More of that anon.

In an extended analysis of the 3 sandstone groups (Altar Stone, debitage and Mill Bay) in the archaeological literature, the researchers focus on the famous thin section 277 (which may or may not have actually come from the big recumbent slab) and suggest that it is more likely to have come from the Senni Beds than from the Cosheston Beds -- although they are equivalent in the Devonian time sequence.  In their discussion of the "Lower Palaeozoic sandstone debitage" the authors point out that most of the samples obtained thus far do not come from within the original stone settings but from the Heelstone ditch, the Greater Cursus ditch and from Roman disturbed sites.  But there also appear to be four samples of the same rock type from genuine Stonehenge contexts.

The research core of the paper is a discussion of past work on sandstone samples from Mill Bay, and new analyses undertaken on fresh samples collected by me (duly acknowledged, with thanks!) and other fieldworkers.  The conclusion is that the mineral composition / petrography revealed in the samples is so different from that of the Stonehenge debitage fragments that Mill Bay can effectively be ruled out as a source area.  The authors say that Mill Bay sandstone fragments are "now considered not to be present within the Stonehenge landscape"  -- in my view they cannot say that, since thus far they only know about a small fraction of what lies beneath the ground surface.  However, it is sufficient -- and quite reliable -- to say that the known samples of Devonian sandstone at Stonehenge appear not to have come from Mill Bay or the Cosheston Beds, and that source areas within the Senni Beds - further to the east -- are much more likely.  That is an important advance.

re the 3 sandstone groups:  Each sandstone is distinctive in term of its minor accessory/heavy minerals (reflecting its source area), diagenetic history as determined by its authigenic cements and clay minerals, and its tectonic and metamorphic history as seen by its clay mineralogy and presence/absence of any tectonic fabric. (p 12)

With respect to the Senni Beds, the authors show a map of their distribution (reproduced above), and say this:

"........for much of this area the outcrop is thin, only widening towards eastern Wales and the Welsh Marches. The composition and relative abundances of the clay minerals in Devonian sandstones systematically varies from east to west Wales (reflecting a change in the metamorphic grade) (Hillier et al. 2006) and preliminary work on the Altar Stone clay mineralogy suggest that the sandstone may be from the east of Wales."

This is interesting, and it will be good to see where this leads -- but a word of caution.  In due course, geologists may well show that some of the Stonehenge fragments analysed may have come from the Senni Beds in eastern Wales.  But that does not mean that that is where the Altar Stone came from. We still do not have absolute certainty that any of the samples examined really did come from the Altar Stone (see also "The Stonehenge Bluestones", pp 172-176 for a more detailed discussion).

See also:
IXER, R. A., BEVINS, R. E., TURNER, P., POWER, M. and PIRRIE, D., 2019. Alternative Altar Stones? Carbonate-cemented micaceous sandstones from the Stonehenge Landscape. WANHM 112, 1–13.

Other posts:


In summary:

What does the paper do?  Well, it provides quite convincing evidence that the sandstone samples reputed to have come from the Altar Stone (stone 80) did not come from the Mill Bay area on the Daugleddau Estuary in mid-Pembrokeshire.

What does the paper NOT do?  Well, here goes:

1.  It does not prove that any of the analysed samples purported to have come from the Altar Stone did actually come from that source.  It follows that the Altar Stone might still be made of Cosheston Beds sandstone.

2.  It does not prove that the "sandstone stumps" numbered 40g and 42c are made of Devonian or Lower Palaeozoic sandstones.

3.  It does not prove the absence of Devonian sandstones from the Stonehenge environs, since the sampled fragments discussed in this and other papers have all come from the 50% or so of the land within the stone settings that happens to have been excavated, and from other sites in the wider landscape.

4.  It does not prove that any of the sandstone debitage has come from stumps 40g and 42c (just as the geologists have not proved that any of the foliated rhyolite debitage at Stonehenge has come from stumps 32d and 32e).  Some of the debitage might well have come from sandstone lumps that were too small to be used in the stone settings.


Entrainment and Transport

In their conclusions the authors wind things up by suggesting that all this somehow has a bearing on the arguments about whether the bluestones were "shipped out" from Milford Haven and along the Bristol Channel or by land along the "A40" route.  They say:  "The new studies instead strongly indicate a number of inland geographical origins for the bluestones; hence a land route is now firmly preferred over a sea route."

There is no mention whatsoever, even from this group of practising geologists, of the glacial transport theory -- even though people like them are supposed to know something about earth surface processes.  There are no citations of the work of Judd, Jehu, Geikie, Williams-Thorpe,  Elis-Gruffudd, Downes or myself, or anybody else who has proposed, with much supporting evidence, that glacier ice could have moved the bluestones.  Geoffrey Kellaway is mentioned, but only in the context of his rather weird idea of a Pliocene glaciation.  That is a strange citation -- but we can understand it as an attempt by the authors to suggest that the "glacial theorists" are fantasists who have lost contact with the real world.  But we are rather more grounded than they may think -- and it is completely indefensible for any serious authors dealing with bluestone provenance to pretend that their ideas are not disputed, and to refuse to consider or even cite a serious literature in the public domain which shows that there is abundant evidence that points to the glacial transport of the bluestones.

So the authors -- not for the first time -- are behaving, in this paper, in an academically reprehensible fashion, and I am amazed that the Editor of WANH magazine has allowed them to get away with it.  He is culpable too.

But hey -- life is too short to spend one's whole time being furious, and the silver lining in this case is that the article in question provides very substantial support for the glacial transport thesis. We know already that the bluestones at Stonehenge (of many different shapes and sizes) have come from around 30 different provenances, mostly in west Wales.  We also know that the "quarrying hypothesis", with respect to Rhosyfelin and Carn Goedog, does not withstand careful scrutiny.  The bluestones at Stonehenge (both orthostats and fragments) have come from a wide scatter of locations, and that in itself is an argument against quarrying for favoured rock types in special locations. Could there really have been 30 bluestone quarries?   Why quarry for a rubbish stone like foliated rhyolite down in a deep valley when better stones could have been picked up from the higher land surfaces round about?  Why quarry for spotted dolerite at the exposed and craggy tor of Carn Goedog, when there were boulders of all shapes and sizes dotted about all over the Preseli hill slopes?

Indeed, why would Neolithic tribesmen have bothered to quarry for monoliths at all, since there is no evidence of any preferential use of specific rock types (eg spotted dolerite, foliated rhyolite, Devonian sandstone, or Lower Palaeozoic sandstone) anywhere in the British Neolithic.  In Wales, cromlechs and standing stone settings were always made of whatever handy lumps of stone happened to be lying around in the vicinity.  It is entirely logical to assume that the same principle of monolith collection and use applied at Stonehenge.

Carreg SamsonSamson, Abercastle.  Just one principle of megalith construction:  use 
whatever stone you've got.  

As indicated in my book "The Stonehenge Bluestones",  entrainment in the compression zone of ice flowing up and over Preseli sits easily with glaciological theory.

Generalised erratic transport routes in South Wales, after many authors.  Note the crossing of arrows. Many erratics carried southwards from the Welsh ice cap were later incorporated into the east-flowing Irish Sea Glacier.

If -- as now appears likely -- the stones at Stonehenge included Lower Palaeozoic sandstones from somewhere in West Wales and Devonian sandstones from somewhere in South Wales, that again militates against targetted quarrying and supports the idea of ice entrainment and transport towards Stonehenge.  There is no problem at all with ice from the Welsh ice cap picking up large blocks of sandstone (or any other rock, for that matter) and transporting these blocks southwards prior to entrainment in the eastward-flowing Irish Sea Glacier at a later stage in a glaciation.  This was realized and commented on more than a century ago by the officers of the Geological Survey (including, ironically, HH Thomas).  

Finally, I am not in the least bothered about where the Altar Stone or the sandstone debitage at Stonehenge actually came from within the outcrops shown on the map of "possible source sandstones".  I am confident that ice did all of the heavy lifting and transportation, and that all our heroic ancestors needed to do, around 5,000 years ago,  was to collect them up from somewhere far to the east, with a view to turning them into an enigmatic monument.  As I have suggested many times, that monument was never finished because the builders ran out of steam and ran out of stones.


PS.  Thanks to Rob Ixer for correcting a slip of the pen.  Duly corrected.