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Sunday 9 December 2012

More on the Nevern Estuary erratics

Chips off one of the erratic boulders in the Nevern Estuary.  This is a high-definition photo, so you should be able to examine the rock quite carefully.....

One of the larger Nevern Estuary felsite (?) erratics, sitting on an exposure of till.

Further to my earlier post about the strange erratics in the Nevern Estuary opposite  Newport,  I have been looking again at the old map (made about 1940) by JC Griffiths, which shows his proposed ice movement directions across NE Pembrokeshire, which coincide broadly with those which I recently proposed.  My earlier post is here:

In other words, Griffiths thought that the last ice might have come from the NNE or NE (in other words, it was Welsh Ice) rather than from the N or NNW (in which case it would have been Irish Sea Ice.

Griffiths noted two main erratic types found in the area -- "Cader and Arans felsite" and "Green Harlech Grit."  There is certainly some greenish grit in the erratic pebbles in the till exposed in the estuary -- and I am increasingly convinced that the larger erratics on the foreshore are similat to those found elsewhere in the area by Griffiths.  The trouble is that "felsite" is a very broad term, used widely in the good old days but no longer accurate enough to tell us what we want to know about the texture and origins of the rock we may be looking at.

But I am mindful of Rob's warnings that nothing other than proper petrography will do here -- and mindful that one must not go on visual identifications alone..........

Developments awaited....

1 comment:

Myris of Alexandria said...

I hear that there might be some new petrography in the offing.
A fragrent whisper that some of Brian's Nevern erratics may be being made as a special Sol Invictus gift for one labouring in the Vinyard. Sublime.

So it is time to look for Micah once again.
best of all the prophets, nice short book.