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Sunday, 24 January 2016

Anglian Irish Sea Glacier limits

This is the BGS map of Welsh ice limits, compiled from various sources.  On it, I have modified the Devensian Irish Sea ice limit in western Pembrokeshire, since it was clearly wrong as published in the Welsh Regional Geology book (2007).

Of much more interest, from the point of view of Stonehenge studies, are the Anglian ice limits as shown by the orange arrows beyond the Devensian ice edge.  We are talking here about an event around 450,000 years ago.  On the map below I have transposed the ice direction arrows on a map which takes an oblique look at SW Britain, showing how the ice might have been channelled or directed by topography.  The yellow arrows show postulated ice movement directions (pretty well supported now by abundant studies) and the extent of Welsh ice at the time.  I have also added postulated isolated small ice caps over Dartmoor, Bodmin Moor, Mendip and Exmoor.  There may have been other perennial ice masses and snowfields as well.

Note that I have refrained from showing ice margins in Cornwall, Devon and Somerset, since this is still a matter of some debate.  But since there are presumed glacial deposits at Greylake, it would have been a very strange matter indeed if the lobe of Irish Sea Ice which pressed into the depression now occupied by the Somerset Levels had not pressed at least as far eastwards as Glastonbury.  What we need now is some hard evidence in place of speculation.....

It's possible that the Welsh Ice Cap of Anglian times was larger than that of Devensian times.  It is also possible that the Anglian ice pushed well inland from the present north coast of Devon and Cornwall -- indeed this is suggested by the erratic distributions which have been described by Paul Madgett.  Just put "Paul Madgett" into the search box if you want to see the relevant posts.

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