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Friday, 27 January 2017

Glaciation of Somerset

I was grubbing about (as one does occasionally, on horrible cold winter days) and came across a very bulky BGS volume on the lithostratigraphy of the British Pleistocene.  Pretty turgid stuff, but somebody has to do it...... anyway, it's all about the correlations of various stratigraphic units from one part of the country to another, bringing up-to-date material from a vast range of published sources.

Above is a re-drafting of a very old map from Gilbertson and Hawkins, giving a carefully considered ice margin for the Anglian Glaciation in Somerset and the surrounding areas.  It's not that different from the maps published by Kellaway, Williams-Thorpe and myself over the years -- based on topographic and glaciological considerations and on all known occurrences of glacigenic materials in Somerset.  You would expect ice to flow more or less as shown, because of the presence of a substantial depression here -- coinciding with the Somerset Levels.

There are now substantial Holocene deposits on the Levels, as shown in the map above.  Note that the ice tongue shown is bounded by the Quantocks, the Blackdown Hills and the Dorset Downs, and on its northern flank by the Mendips.  We have discussed the Mendips many times before on this blog....... I still think they might have been overridden by glacier ice.

I have also been interested to read recently that Campbell and Bowen, the editors of the Welsh GCR volume, consider it quite likely that the Cotswolds were overridden by ice during the GBG (greatest British Glaciation) -- which would push the ice limit of Gilbertson and Hawkins further to the east.

I'm amazed that certain archaeologists (who shall be nameless, for fear of upsetting Myris) seem to be blissfully unaware of this material, which they certainly should have found if they had bothered to do a search or if they had talked to academic colleagues from related disciplines.  They still insist that the ice never flowed eastwards, never flowed uphill, and never crossed the coasts on the eastern side of the Bristol Channel.

More to the point, I'm intrigued to see that the BGS personnel charged with writing this mammoth Report have apparently accepted that the Gilbertson / Hawkins line for the extent of Anglian ice is reliable -- or at least reasonably so.  This is not "fringe science"  -- some people need to get used to the idea that this is the state of current thinking in the geological / geomorphological community.


British Geological Survey Research Report  RR/10/03
A lithostratigraphical framework for onshore Quaternary and Neogene (Tertiary) superficial deposits of Great Britain and the Isle of Man
A A McMillan, R J O Hamblin, J W Merritt
British Geological Survey    2011



TonyH said...

We need to make sure Professor Tim Darvill of Bournemouth University is made aware of these findings that the Cotswolds were overriden by ice during the Greatest British Glaciation. Tim has studied the Cotswolds Neolithic archaeology over many years as well as being a prominent specialist in this period throughout Britain.

BRIAN JOHN said...

Tony -- what they suggest is that there is a POSSIBILITY of the Cotswolds were submerged beneath ice on at least one occasion. Campbell and Bowen say, as do many others, that the evidence is very subtle and difficult to interpret. Their reasoning for suggesting an ice cover is the presence of Welsh erratics in the Thames drainage system -- they say that they could not have got there unless ice had passed over the Cotswolds. Again the Anglian Glaciation seems to be the preferred candidate......