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Some of the ideas discussed in this blog are published in my book called "The Bluestone Enigma" -- available by post and through good bookshops everywhere. Bad bookshops might not have it....
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Saturday, 29 January 2011

Something strange at Nunney

Over the years I have seen a number of references to a strange deposit at Nunney, a small village in Somerset which lies due west of Stonehenge.  The above map shows Geoff Kellaway's reconstructed glacial route, showing the Irish Sea Glacier passing over Nunney on its way to Stonehenge.  leaviung aside for the moment the queestion of whether the ice actually did reach Stonehenge, what is the deposit at Nunney?  Rodney Castleden describes it as a "drift deposit" -- a reddish-brown sandy clay containing both chalk and flint fragments, which means it is not directly related to the underlying bedrock.  Castleden suggests that the deposit has come from the EAST -- from the chalk escarpment -- and that the material was transported in mudflows during the cold phases of the Ice Age.  Hmm -- that sounds a bit strange to me.  On the other hand, Kellaway's explanation is equally difficult, since he thinks that the chalk and flint blocks have come from some chalk outcrop at an unknown location to the north or west.

In his famous (infamous?) Nature article in 1971, Kellaway described the Nunney deposit in some detail.  Actually, it is at Holwell, just outside the village at grid ref ST72554523, where there are large limestone quarries.  The deposit was observed when the land was being cleared for one of the quarries.  The reddish clay was seen to be up to 1m thick, resting on Inferior Oolite (Jurassic) limestone.  It was thin and patchy, and was partly decalcified, but the deeper pockets contained rounded and subangular fragments of white chalk (thought to be from the Middle Chalk), flint, chert, quartzite, Carboniferous and Jurassic limestone.  Kellaway thought that this deposit was related to other glacial deposits on the limestone uplands on the eastern margins of the Mendips, at an altitude of c 152m.  He also thought that at one time the ice extended at least as far east as the "western approaches of the vale of Pewsey."

What are we to make of the Nunney (Holwell) deposit?  Well, it so happens that my son and his family live in Nunney -- next time I go to see them, I am minded to pop over to those quarries and to see if any of that strange reddish deposit is still to be seen, forty years after Kellaway.......

It might well be a till, incorporating fragments from relict weathering deposits or residuals which accumulated to the west during a long process of denudation.  Another possibility is that the deposit incorporates gash breccia material which has come from the Nunney Fault.  Watch this space....

6 comments:

TONY said...

What are your current views on the possibility you alluded to in "The Bluestone Enigma" (page 118) of glacial deposits (and maybe the remnants of a terminal moraine) somewhere near Bradford-on-Avon near the confluence of the Avon and the Frome rivers?

BRIAN JOHN said...

I was citing a number of people who have speculated that since there appear to be old glacial deposits at Greylake and a number of other sites within the Somerset levels embayment (with more recent deposits on top of them) the ice of the Irish Sea Glacier might have extended as far as the chalk escarpment.

Finds of old deposits are incredibly hit and miss -- I'm constantly reminded how little we know about the superficial deposits and sediment sequences of Somerset and Wiltshire -- often, discoveries are down to chance (road widening schemes, construction of new housing estates etc) and even then, if there is nobody around to interpret what gets uncovered, exposures get covered up again and the story is lost. I still think it's a fair bet that something is lurking out there, waiting to be discovered....

TONY said...

Your mention of how discoveries are often down to chance through human development schemes makes me think we could do with the present generation of Undergraduate Archaeologists being trained to LOOK OUT FOR such exposures when they are (often temporarily) revealed, as well as conducting "watching briefs" for archaeological features. Shame that current Government economic policy may reduce the number of archaeologists working in liaison with commercial outfits.

BRIAN JOHN said...

I agree. Archaeology is reasonably well served because legislation makes it a requirement for large projects (eg pipeline construction etc) to have an archaeology team on hand to document anything interesting that comes up, Isn't that what keeps Archaeology Trusts in gainful employment? I would like to see a similar requirement for geomorphology and geology! I still feel sad that none of the big pipeline projects running east from Milford Haven (which provided several slices through the sediments of west and South Wales) was properly monitored by trained observers. Think of all those sediment sequences and erratics that have gone unrecorded....

TONY said...

Yes, these would all be valid and beneficial ways of adding to the sum total of human knowledge.

TonyH said...

Brian, in the 3 years that have since elapsed, have you managed to take a look for the Holwell deposit near Nunney?

I often walk along the River Frome between Rode and Tellisford, north of Frome town at grid ref 80605500 and northwards on the next O.S.Sheet. There appears to be evidence of a much wider river, judging by the raised bank on the eastern side of the Frome in particular.