Interim 2018 dig report from the "great circle" hunters.........

Courtesy of Bluestone Brewery, just up the road, the interim report from MPP et al on the 2018 dig is now in the public domain.  He confirms that there will be no dig this year, but expresses the hope that the diggers will be back in 2020.  Here we go again.........

I'm a bit pushed for time at the moment, but here is a link for those who want to take a look.  My initial impression is that MPP is as determined as ever to ignore the fact that much of his bluestone quarrying / Stonehenge / Waun Mawn  evidence is hotly disputed.  We have looked at these irregular indentations in the ground before, in earlier posts, and one has to admire the sheer effrontery of these guys in claiming without a shadow of a doubt that they are stone holes or sockets that once held monoliths!  I wonder if any other archaeologists have looked at them, and agreed?  Anyway, enjoy, and I shall come back to this in more detail in due course.

https://www.bluestonebrewing.co.uk/wp-content/uploads/2019/05/Waun-Mawn-2018-interim-report-lite.pdf

By the way, MPP is giving his annual jolly brewery talk early this year, as it happens on my birthday, 27th July.  Happily I shall be away, doing a spot of quiet kayaking in the Stockholm Archipelago.

Anglesey and Pembrokeshire -- both subjected to areal scouring?

A comment from a mysterious contributor the other day has got me thinking about the similarities and differences between Anglesey and Pembrokeshire with respect o the history of glaciation.  They are both lowlands located away from the bulk of the Welsh upland massif and its Welsh Ice Cap which waxed and waned during the Devensian glaciation and presumably during other glaciations as well.  In both regions superficial deposits are thin and scattered, and in both regions there are no marked uplands, and instead a sequence of undulating and gentle ridges and depressions which expose the "grain" of the country -- related in turn to the structures and textures of the underlying rock types.

Anglesey has quite prominent streamlined bedrock features, aligned broadly NE - SW, as noted in this article by Lee et al (2015):

Lee, J.R., Wakefield, O.J.W., Phillips, E. & Hughes, L. 2015. Sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications: an example from Anglesey, north Wales, UK. Quaternary Science Reviews 109, 88-105.

http://nora.nerc.ac.uk/id/eprint/509384/1/Lee_et_al_QSR_2015.pdf

Quote:

The Quaternary deposits of Anglesey form a thin and discontinuous veneer that mantles the bedrock. The most prominent superficial deposit is a diamicton containing far-travelled erratic lithologies sourced from bedrock strata within and surrounding Irish Sea Basin. This diamicton is synonymous with the ‘Irish Sea till’ (Greenly, 1919; Campbell & Bowen, 1989; Williams, 2003; Thomas & Chiverrell, 2007; Phillips et al., 2010) which forms part of the Irish Sea Coast Subgroup of the Caledonia Glacigenic Group (McMillan & Merritt, 2012). The till was deposited extensively around the Irish Sea Basin by the Irish Sea Ice Stream during the Late Weichselian (Devensian; MIS 2) glaciation (Figure 1c). The overriding of Anglesey and the adjacent offshore area by the Irish Sea Ice Stream led to the sculpting of the substrate and development of streamlined bedrock features (e.g., streamlined bedrock, roche moutonée, rock-cored drumlins) and sediment- to bedrock-cored (e.g. drumlins) subglacial bedforms (Hart 1995; Thomas & Chiverrell, 2007; van Landeghem et al., 2009; Phillips et al., 2010). These landforms and locally-preserved glacial striae record an overall ice-movement direction from northeast to southwest across Anglesey. The Irish Sea Ice Stream was one of several ice streams that drained the interior of the last British Irish Ice Sheet (Figure 1c) (Evans et al., 2005; Bradwell et al., 2008; Hubbard et al., 2009; Clark, C.D. et al., 2012; Clark, J. et al., 2012). At its maximum extent (c.24-23 ka BP) the ice stream occupied much of the Irish Sea Basin and was fed by glaciers emanating from western Britain and eastern Ireland (Knight et al., 1999; Clark & Meehan, 2001; Hiemstra et al., 2006; Roberts et al., 2007; Greenwood & Clark, 2009; Scourse et al., 2009; Rijsdijk et al., 2010; Clark, J. et al., 2012; Chiverrell et al., 2013).

In Pembrokeshire the "grain" of the country is not so easy to pick up, except in the south.  If you look at the following maps, this is apparent. (Google Earth satellite images are not so easy to interpret, because they have too much clutter on them........)

Low definition LANDSAT image of Pembrokeshire.  On this, the grain can be picked up, but it is much clearer in the south.

A simplified map of the structure of Pembrokeshire, with info extracted from BGS mapping material.

The grain can be tied in with the features of the geology map, but note that the strips of Ordovician igneous rocks in the core of the Preseli uplands are NOT easy to pick up in the satellite imagery.

Now let's tie these images in with what we know about directions of ice movement across Pembrokeshire.

This map incorporates information from many sources on ice movement directions, and can be taken as representing a "best fit" for the Anglian Glaciation, around 450,000 years ago.

This map by JC Griffiths (1940) is based on erratic distributions, taking no account of possible zig-zag routes and movements of single erratics across several glacial episodes.  Note that there are differences with the "Anglian" map above.  

Griffiths has Irish Sea ice coming across the north Pembrokeshire coast directly from the north.  He also shows central and southern Pembrokeshire affected by an ice stream flowing from NW towards SE. On the Anglian map we have a more westerly component, with ice moving from WNW towards ESE.

So what is the evidence for streamlining? I have to say that there is none in north Pembrokeshire, but that in south Pembrokeshire there is a degree of alignment between the "grain" of the country, the known structural trends, rock outcrops, and ice movement directions. Cause and effect?  Now that's very difficult to establish.............

Exposures of the submerged forest at Borth

Very extensive areas of the submerged forest at Borth have been exposed in the last month or so -- unusual because the stripping away of the covering sand has not been a result of extreme storm events.  There is much speculation as to what is going on -- there may be a link with coastal defences changing the characteristics of longshore drift and tidal currents, or the phenomenon may be entirely natural and cyclical.

More info here:

https://www.walesonline.co.uk/news/wales-news/stunning-ancient-forest-welsh-beach

Abandoned glacier troughs -- High Arctic

Devon Island

North Greenland (Peary Land)

 

NE Greenland

These are very cold and dry regions, and although there are many ice caps and outlet glaciers there are also very expansive areas of ice-free land where permafrost features predominate. 

But massive abandoned glacier troughs are to be found in many areas, attesting to a past much more expansive glaciation by the Greenland ice sheet and from independent ice caps on the islands of the Canadian Arctic archipelago and in north Greenland.  I must investigate further.......

PS.  You can see a few other posts on glacial troughs if you put "glacier troughs" or "glacial troughs" into the search box.   Shortly before leaving Durham University in 1977 I started some research on "brutalised trough patterns"  -- but I never finished it.  One of my regrets......

Anyway, a classic area of brutalised troughs is to be found around Akureyri in northern Iceland, as featured on the front cover of our text book:

Such troughs are created (maybe over the course of many glaciations)  where there is a very heavy discharge of ice from one source area, with very few supplementary discharges coming in from the flanks -- leading to a "brutal" truncation of many of the interfluves and subsidiary valleys that might have existed at some earlier stage.

Atlas contributions

It was a privilege to be invited by the learned academic panel responsible for this volume to write and illustrate the first part of the Atlas -- Part One: The Physical Setting, on pages 20-26.   It's good that some stalwart members of the academic establishment recognize my credentials and my ability to contribute something worthwhile -- even if certain archaeologists seem to think that I don't actually exist, except in nightmares.  So there we are then, as they say in these parts.

My four sections are entitled Geology and Structure, Landscape and Natural Regions, The Ice Age, and Superficial Deposits and Habitats.  With each map (or set of maps) I provided, explanatory text, notes and references.  Here are the maps.  Click to enlarge.

 

The Pembrokeshire Historical Atlas

This impressive historical atlas of Pembrokeshire has just been published as the culmination of the 5-volume official county history.  Edited by Prof DavidHowell, it contains 82 "topics" with maps and other illustrations on odd pages and explanatory texts on the facing (even) pages.  It's a large format book (28 cms x 28 cms) and runs to 205 pp.  References and notes are all gathered together at the end of the book.  The cover price is £30, and it's available via the Pembrokeshire County History Trust.

I was asked to provide the maps and text for Part Two of the book, on the physical setting.  More of that anon.

Topic 12, on Bronze Age Pembrokeshire (2500 - 800 BC) is by Tim Darvill.  There is a brief mention of Stonehenge and the "quarries" of Carn Menyn, Carn Goedog and Rhosyfelin -- and it's interesting that he considers them to be Bronze Age features rather then Neolithic ones.  Not at all sure how he squares that with the radiocarbon and other evidence from Stonehenge.  He also drops into the mix the idea that eastern Preseli was a significant or special area across several millennia -- and shows a number of features on Map 12C purporting to be Bronze Age "ceremonial centres".   Sadly, he does not tell us what a ceremonial centre is or was, and the precise locations are not named.  Does a supposed Neolithic quarry count as a "ceremonial centre"? Special pleading and ruling hypotheses come to mind.........

Darvill speculates as to why "more than 80 blocks of stone were carried from Mynydd Preseli to Salisbury Plain".   There is nothing new here -- and in the grand tradition of senior archaeologists thinking, talking and writing about bluestones, he fails to mention that there is a dispute going on,  fails to cite inconvenient research findings, and fails to give any mention at all of the glacial transport hypothesis.

It's a pity that a splendid volume like this should be marred by slapdash academic writing on some of its pages.

  

The jolly Stonehenge Quiz ---- what's the "right" answer?

Somebody complained to me the other day (why me, for goodness sake?) about the Stonehenge quiz published in the EH members magazine in October last.  They said, quite rightly, that the "correct" answer to the question about the bluestones was misleading, to say the least.

https://www.english-heritage.org.uk/members-area/members-magazine/october-2018-20-questions-quiz/

What do you think?

Neither the answer nor the added explanation should go unchallenged.

Not all of the bluestones are from the Preseli Hills -- but most of them almost certainly are.

The supporting wording is carefully chosen, but it is far from adequate.  It is thought by whom?  And ".... to bring the bluestones to Stonehenge"??  That assumes the correctness of the human transport theory.  EH should be honest enough to accept that there is a dispute going on.  The explanation should be this:

The mode of transport is disputed.  Some archaeologists believe that the stones were carried across land and sea by Neolithic tribes, but some earth scientists are convinced that the stones were moved to Salisbury Plain by glacier ice.  

To repeat -- it's really rather weird that EH seems to be incapable of using the word "dispute" -- maybe in the belief that an academic dispute would cause the public to become confused, or dilute the romance of the ancient stones.   Less emphasis on narrative and storytelling, and more on scientific accuracy, if you please......