Erratic behaviour in the Midlands

 Pic:  Valerie Kedge

Strange goings-on in the Midlands these days.  Suddenly, they seem to have discovered that glacial erratics are rather interesting.  Better late than never.  Once upon a time, before people started messing about with the landscape and built Birmingham and its suburbs, there were vast expanses of glacial and fluvioglacial deposits (and some pro-glacial lake deposits too) in the south Midlands, with some clearly delineated landforms including terraces in river valleys, and thousands of glacial erratics scattered across the landscape.  As in other glaciated areas, most of these erratics were cleared away over thousands of years of land clearance, leaving just a residue of the larger ones that nobody could be bothered to move.  I suppose that some were incorporated into dolmens and round barrows, and some (if they had convenient pillar-like shapes) would have been put up as standing stones too.

There is plenty in the literature about these Midlands erratics, including protracted discussions about ice movement directions and provenances.  Many of the old geologists were good at rough provenancing, although of course their identifications of sources and the names used for rock types have changed over time.

This brings us to the recent fun and games relating to one particular erratic boulder at Northfield in the southern suburbs of Birmingham.  Somebody decided it would be a good idea to flag up its importance and to stick up a plaque in its honour.  It's called "The Great Stone" and it is currently located within the village pound.  Next door is the Great Stone Inn, so no doubt the stony attraction will bring in a bit of extra trade.........

It appears that there was an interest in the probable provenance of the stone, which was assumed to have come from the Arenig volcanic sequence around Snowdon in North Wales.  A sample of the rock was sent to Rob Ixer, and he confirmed the provenance, and in exchange for his hard work he was invited to unveil the magnificent new plaque at a grand civic ceremony earlier this month.

See this:
http://earthwise.bgs.ac.uk/index.php/Arenig_Series,_Ordovician,_Wales

The media coverage of this magnificent event is so garbled and nonsensical that we had best stay well clear of it, for fear of causing embarrassment........

You can find out more about the Birmingham erratics (mostly reliable info) here:
http://geologymatters.org.uk/2012/02/16/erratic-ice-of-the-black-country/
bcgs.info/pub/wp-content/uploads/newsletters/BCGS_Newsletter207.pdf
bcgs.info/pub/wp-content/uploads/newsletters/BCGS_Newsletter206.pdf 
http://brummiesguidetobirmingham.blogspot.co.uk/2012/07/glacial-erratics-in-bournville.html 
http://brummiesguidetobirmingham.blogspot.co.uk/2013/02/glacial-erratic-university-of-birmingham.html

This is more or less what I sent to Rob, when he asked what the context might be:  In terms of its Quaternary history, the Birmingham area is completely chaotic -- it seems that Devensian ice did not reach south Birmingham, but Anglian ice certainly did.  And some people think there was a third glaciation -- the Wolstonian -- that reached the area too -- but the evidence is hard to interpret.  There have been glacial lakes too -- to add to the confusion.  My best guess is that Snowdon erratics got into the area at some stage in the Anglian -- but towards the peak of that glaciation the most powerful ice stream came in over the Cheshire Plain -- it's called the Eastern Irish Sea Ice Stream.  Snowdon erratics could therefore have been moved several times -- following a somewhat erratic course.  You could also get erratics in that area from the Irish Sea Basin (including Scotland) and also from northern England, because Pennine ice was also coming south across the area at some stage.  That all adds up to an extraordinary mishmash of erratics from all over the place. 

 One interesting sidelight on all of this relates to the Stonehenge Altar Stone.  It will be recalled that it sits rather uneasily with the assortment of other bluestones at Stonehenge, which have come from north Pembrokeshire.  I have argued earlier that the route followed to the Altar Stone probably involved initial carriage by Welsh Ice from a source area in the Brecon Beacons or in one of the South Wales Valleys, and then carriage by a part of the Irish Sea ice stream towards its final resting place.  As in the case of the Great Stone at Northfield, we are talking about the Anglian Glaciation, around 500,000 years ago.  Another erratic route for an erratic boulder.........