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Tuesday 23 February 2021

Geology sampling progress

 


Many thanks to Tim Daw for publishing this map on his blog and on Twitter and putting it in the public domain.  Excellent -- congratulations to MPP and his team for getting on with this at long last!  I have been urging them for the last five years to do much more extensive sampling of the Fishguard Volcanics rhyolites, ashes and welded tuffs in the Brynberian Valley, in the hope of either confirming the presence of a "bluestone quarry"at Rhosyfelin, or disproving it.  There are lots of outcrops, as I have pointed out.  I don't know what the star colours indicate, but  there seems to be quite intensive sampling up and down the Brynberian Valley between Brynberian, Crosswell and the deep gorge-like section of the Afon Nyfer near Felin y Gigfran.  I hope they will sample the foliated rhyolites, where they find them, both along fracture planes and perpendicular to them -- so as to pick up depth or age-related variations in the foliated layers.   From a purely geological point of view (forgetting about quarries for a moment) the results are likely to be fascinating.  It looks as if there is much more intensive sampling of Rhosyfelin and Pont Saeson as well.  All good.

The other sampling areas chosen are to the NW of Carnedd Meibion Owen (dolerite on the tors but not elsewhere) and in the country running through Ty Canol Wood and towards Pentre Ifan cromlech.  I have some thesis maps from Daniel Lowman for that area -- the geology is really complex, including ashes, lavas and welded tuffs. I think the rocks are mostly ashes around the Pentre Ifan cromlech, in the stone walls and the big slabs of rock lying about in that area.  It will be interesting to see what turns up.

In setting up this new research exercise, it's good to see an unspoken acknowledgement from the geologists (Rob Ixer and Richard Bevins) that their "spot provenancing" claim for the Rhosyfelin rock face is not adequately supported by the data collected and presented.  They need more information, and they need it soon........ and that's a point made not just by me.

As I have also stated often on this blog, MPP and his team also need new digs in the Brynberian and Nyfer valleys at "control sites" in order to support their claim that the history of occupation at Rhosyfelin (as indicated by the wide spread of radiocarbon dates) is unique, and specifically associated with Neolithic quarrying activity. i hope they have taken that on board, and that it will play into their decision as to where to dig next.

I'm intrigued that there seems to be no sampling in the Waun Mawn area, and no sampling indicated for the areas of dolerite or spotted dolerite.  That work is as badly needed as the work on rhyolites -- but let's wait and see.  Maybe Tim has another map that he will show us in due course, officially released from Project HQ......

Pentre Ifan cromlech, made from rocks (volcanic ashes) used where found.....

Something igneous and complicated, on one of the tors at the top end of Ty Canol wood.  I wouldn't like to hazard a guess as to what this rock is called...... maybe a welded volcanic agglomerate?



1 comment:

Tony Hinchliffe said...

Tim, like me, was at last night's Zoom talk emanating from Wiltshire and titled: Latest Archaeological News. He also asked this question: Would digging up Hawley's Graves be worthwhile? [they are buried in pots to the South of Stonehenge].

The Zoom discussion MAY go onto YouTube in due course.