The use of local stone in prehistoric stone settings

Pentre Ifan, built of slabs of locally collected volcanic ash.  

Photo courtesy Hugh Thomas

Hugh Thomas, over on the Preseli360 Facebook page, has just published an interesting post which I am very happy to acknowledge and reproduce below. 

Nobody knows the stone settings of Preseli better than Hugh, and I agree with  him that there was apparently no interest at all, in the prehistoric poeriod, in collecting stones from far away and transporting them from A to B just so that you could build them into your friendly neighbourhood cromlech.

Stephen Briggs called this opportunistic, utilitarian and pragmatic.  He could not see in this area any evidence of monoliths of certain rock types being valued above any others, or deemed to be sacred or special.  Some monoliths (like dolerite, hard sandstone, volcanic ash or lava) were obviously better for building with than flaky rhyolite, shale or mudstone -- so they tended to be used if they were available.  

But long distance stone moving expeditions?  No thanks.  Our ancestors were too smart for that sort on nonsense..........

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

QUOTE

Just a personal thought that has reoccurred to me a number of times over the years...
There are many spectacular quartz boulders to be found in Preseli, and there is certainly a concentration of them around the Bwlch Ungwr , Carn Breseb and Carn Alw area.

If in ancient times stones were being revered as being special and " being moved about" , then why pick stones that all on appearance alone all looked the same and that only modern geologists can largely REALLY tell apart ? To my artistic eyes the most spectacular stone setting would have been a white quartz stone circle and there were MORE THAN ENOUGH quartz boulders around to create that ...I can not imagine for one moment that our ancestors would not have been fascinated by the white gleaming quartz .

Just imagine a quartz circle gleaming in the sunlight or glowing under a full moon, it would have been stunning .

To me this gives weight to the cold fact that any stone setting found around Preseli is made up of stones that were found in the immediate area for convenience...

I have not yet been shown anything or seen anything in Preseli that tells me otherwise, but if the truth of it IS otherwise I am very open to be shown it, because it would be the truth and not just a romantic belief. But the facts supporting the movement of stones would have to be overwhelming and not just theories being shoehorned into this landscape as has been really all along. ..

Those championing theories of stone movement seem to actually rely on the curiousity of people not looking into things TOO closely from the point of view of practicality , because that is when all the problems begin and an unraveling of the theory means it takes further more colorful claims to hold it together, and begins to become impractical from the point of view of human nature. .

I am happy for anyone to show me otherwise , but as it stands , in 2024, despite all I have been shown or read just demonstrates people were here at that time and not transporting stones over great distances in Preseli , the stones left at Waun Mawn ARE from that area and so on .. Nothing has peaked my curiosity to question further ...Yet ..

I am grateful to those who help to keep a sense of practical balance on all of this ..

The inner reaches of Nordvestfjord

 I found a higher resolution copy of this fantastic image of the inner reches of Nordvestfjord. We are looking down the fjord from above the snout of Daugaard-Jensens Glacier, with ntabular bergs and quite extensive sea ice.  To the left of centre there is a low plateau with a thin ice cap, and higher icefields are shown in the distance to the right of centre.

In the far distance, towards top right, we can see the fjord section where the fjord sides are almost vertical and where the fjord scenery is at its most dramatic.

So why the difference between the relatively gentle ice-scoured and moulded slopes of the upper fjord, and the hugely spectacular fjord landscape in its middle and outer sections, towards Hall Bredning and Scoresby Sund?  Well, we don't really know the full picture, but the simple answer must be that the extent of fjord deepening -- and maybe fjord widening too -- is a function of ice discharge.  As the ice of the Nordvestfjord Glacier moved south-eastwards it was supplemented by the ice flowing in from many tributary glaciers over a distance of c 120 km, leading to a gradual stepped deepening of the fjord floor.  Then, as soon as the glacier emerged from the mountain front into the broad embayment of Hall Bredning, it lost its erosive capacity at the threshold and spilled out sideways via a number of diffluent discharge routes.  Just like Hardangerfjord, Sognefjord and many other big fjords throughout the world.......

https://brian-mountainman.blogspot.com/2013/07/nordvest-fjord-east-greenland.htmlhttps://brian-mountainman.blogspot.com/2013/07/nordvest-fjord-east-greenland.html

https://brian-mountainman.blogspot.com/2021/09/the-nordvestfjord-threshold.html

  

Renland dissected plateau

 

On the southern and eastern ringes of the Renland Ice cap (adjacent to Nordvestfjord in East Greenland) there is a plateau landscape which has been heavily eroded by streaming ice and thus heavily dissected. See also the posts on Grundvikskirken, the most spectacular rock pillar of all...........

This landscape is different from that of the Staunings Alps because of the advanced stage of the highly selective linear erosion, with streaming ice cutting vertically down to create troughs now occupied by water (in the fjords) or rapidly flowing ice (in the dry valleys).

Much work remains to be done on Renland -- but in the meantime we can enjoy the fantastic images being assembled by the climbing groups who are attracted to the area.

This is the Renland ice cap in an oblique aerial photo.  Some of the rocky ridges beyond the edges of the ice cap are heavily dissected into spectacular towers and pinnacles.......

Glaciated landscape types

 

I have been looking at some new images of the Staunings Alkps in East Greenland, in what we might refer to as a classic Alpine landscape.  It's heavily glacierized, with no plateau ice caps or snowfields.  Almost all of the snow and ice is found in hollows or depressions, separated by a multitude of sharp peaks, jagged "sawtooth" ridges and pinnacles.  Slopes are very steep, and frost processes dominate in the destruction of bedrock outcrops.  Avalanches and snow bank collapses are frequent.  

This landscape stratches from hoirozon to horizon, and is revealed in all its glory in footage from a low-altitude (5,000m) overflight in a chartered Airbus aircraft, on its way to the North Pole. 

There are thousands of spectacular peaks here, most of them still unclimbed.  But we can understand why the Staunings Alps are now something of a magnet to climbing expeditions........

One thing that I find particularly intriguing is the transition from "alpine country" to "plateau and fjord country" on the northern, western and southern flanks of the mountains.  Look at this photo:

The contrast is staggering -- within a few miles we pass into an old plateau landscape where most of the snow and ice is found on extensive or broken plateaux.  The plateau segments are separated by deep troughs containing outlet glaciers, and there are many places where ice spills over the plateau edge in spectacular "frozen cascades".  

What is the explanation for the differences between these landscapes?  Watch this space.........

Landscape types to the north of Scoresby Sund.  The red line encloses most of the Alpine terrain.

Satellite image of the Staunings Alps / Werner Mountains area

West Angle then and now

 

I still think West Angle is one of the most important interglacial sites in Wales.  I found the above B/W photo in an old box file, dating from the 1960s.  Now, sixty years later, the brick pit has been filled in and the drift cliff is so degraded that I am not sure we can trust the stratigraphy any longer.  It was difficult enough as it was, before all the recent slumping and vegetation disturbance.........

Ailsa Craig -- where all those erratics came from

 

 

Lovely photo of Ailsa Craig in the winter.  There is more of it under the water, of course -- but it's nice to remind ourselves now and then that this is the source of many thousands of small (and very characteristic) white microgranite erratics found around the shores of the Irish Sea and St Georges Channel.

More doubts about the "cold climate" raised beaches of southern Ireland

The Courtmacsherry raised beach exposure.  Overdependence upon OSL 

dates is not a good idea.

P 175 of O'Cofaigh et al, 2012
Quote:
Undoubtedly there is extensive evidence for the beach along the south coast of Ireland forming in a cold-climate environment (see above), and indeed some of the evidence which underpins this interpretation was first noted by Wright and Muff (1904). This includes the presence of erratics within the raised beach gravels and interbedding of the beach gravels with periglacial slope breccias. Previous investigations of the sand facies that overlie the raised beach at sites such as Howe's Strand and Broadstrand have interpreted it as ‘blown sand’ (e.g. Synge, 1978). This is inconsistent with the sedimentology of these sands which exhibit well defined hummocky and swaley cross-stratification consistent with a shallow marine rather than aeolian setting. Thus the facies sequence of raised beach/HCS sands/SCS sands indicates submergence following beach formation. Periglacial slope deposits and isolated angular clasts of local bedrock within these sands indicate the maintenance of a ‘cold’ depositional environment during this submergence.

Sorry chaps, but I beg to differ.  There is NOT "extensive evidence".......  I have gone through the stratigraphic descrtiptions very carefully, and I see NO evidence that the climate was cold at the time of beach formation.  The raised beach and associated sands do not show any evidence of a prevailing cold climate.  There are no signs of a cold climate shell fauna in the beach gravels and sands, and no trace of a warm climate fauna (as in the Patella Beach) either.  There seem to be no examples of interdigitated glacial materials in the raised beach or in the sands.  There is either a clean break between the beach materials and the overlying slope breccia, or some interdigitations of broken bedrock materials, but no evidence is presented to demonstrate that the breccia accumulated under cold climate conditions. The breccias most likely represent local rockfalls and scree accumulations following  a shift in coastline position.  This could be established with reference to the details of coastal morphology and the positions of the local rock cliff.

There appear to be no glacitectonic structures or erosional contacts in the raised beach materials which might indicate the presence of a local ice front.

The fact that the overlying sands are interpretd as shallow marine beds rather than blown sands has no bearing on the "cold climate issue".  And the presence of occasional angular clasts in these beds simply suggests that there were localised rockfalls nearby, or some incorporation of glaciated clasts from the disaggregation of older (pre-existing) glacial deposits on the adjacent coastline.

The junction between the raised beach and the breccia is essentially no different from that which we observe at Poppit, Ogof Golchfa, Broad Haven South and many other locations on the other side of St Georges Channel, in Pembrokeshire.  It is most realistic simply to interpret this junction as representing the climatic shift from interglacial (Ipswichian) to cold climate (Early Devensian) conditions, as concluded by many researchers over many decades.

So the only evidence (as far as I can see) of the cold climate environment is that of the OSL dates.  That's not a good situation.  What if all of those dates are faulty, as a result of faulty calibration or a systematic under-estimation of the ages presented by the authors of this paper?  We all had to learn some pretty harsh lessons from the chaos of amino acid dating a few decades ago, which was so serious that it brought much of the work of the Geological Conservation Review volumes on Wales and the Soutrh-West of England into question.  We await further views on the reliability -- or otherwise -- of the dates.  In the meantime, a degree of scepticism is in order.

See also:

A Marine Isotope Stage 4 age for Pleistocene raised beach deposits near Fethard, southern Ireland
Colman Gallagher, Matt W. Telfer, Colm Ó Cofaigh
Jnl of Quaternary Science, Volume 30, Issue8
November 2015
Pages 754-763

First published: 06 October 2015
https://doi.org/10.1002/jqs.2808

https://onlinelibrary.wiley.com/doi/10.1002/jqs.2808

Quote from Prof G Duller, Aberystwyth:

Samples from sediments whose grains were exposed to daylight during transport or deposition date the time of transport or deposition.The most suitable sediments are those that were exposed to the most daylight during transportation, including wind-blown sands and silts.The optically stimulated luminescence (OSL) signal from minerals is more rapidly reset by daylight than is the thermoluminescence (TL) signal (Fig 8). OSL measurements have made it feasible to look at fluvial and colluvial sediments as well, but care needs to be taken in these cases to assess whether they were exposed to sufficient daylight at deposition to reset the luminescence signal being measured.

Duller, G. A. T. (2008). Luminescence Dating: Guidelines on using luminescence dating in archaeology. English Heritage.