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Saturday, 28 April 2012

Spotted dolerite on Carningli





I have mentioned before that I have seen spotted dolerite boulders on Carningli, near Newport -- but I an not at all sure where the outcrops are.  Well, today, on my walk on the mountain, I came across several very large erratics which seemed to me to be typical spotted dolerite not dissimilar to the spotted dolerites of the Carn Meini area in eastern Preseli.  Click on the photo above to enlarge.  The stone is a bit dusty and dirty, but note the distinctive white flecks or crystals scattered through the grey-blue matrix.  I must go back when there has been some rain, so that the surface is wet and clean -- and next time I'll go with my hammer as well as my camera.......

3 comments:

chris johnson said...

Interesting.
Just spent today in northern preseli and visited rhos-y-felin. Difficult to conceive of these rocks being moved over the Prescelli ridge by glaciers. A while back I speculated that river transport down the Nevern might be a possibility but forget that, at least the way the terrain is nowadays. I also noticed there are a lot of megaliths around in field boundaries and as gateposts - I even discovered one in the middle of a field that is not on the OS map! Big deal for me.

By the way Brian, there was a guy clearing a stone walled lane of stones on the way down towards Newport from Cilgwyn on the right side of the road. The adjacent field is now storing many interesting looking stones - next step a garden centre in Cowbridge perhaps? It seems outrageous that someone can just rip up one of these lanes. I suppose he can't get his 4x4 up to his country cottage.

Another curious question. A while back we talked about white quartz stone. There is a lot of this around. Does this outcrop naturally? If so where? There are thousands of pieces from Glandy Cross to Brynberian. Many fist sized lumps with one crudely worked surface, other skull sized and worked all-around, and some small boulders embedded in hedgerows.

I thought of dropping in to visit but then I thought you were probably out and about on such a wonderful day. I look forward to hearing from you, especially on all that white quartz.

BRIAN JOHN said...

Hi Chris -- I am offended that you didn't call in! I was probably around -- if you come over this way again, pop in and say hullo! Might be a cup of coffee on the go -- you never know...

Yes, bluestone slabs, pillars and gateposts everywhere.

The field adjacent to the Cilgwyn Road is the one where I found those red sandstone boulders described in the other post. Lots of interesting stones there. The field is owned by Dai JCB, who is smoothing it off -- it was very rough before, full of debris from a rubbish dump that was at the top of the slope. Not sure if that is the place you looked at....

Quartz everywhere too -- there are veins all over the place, and they are so common in the cliffs between Newport and Cwm yr Eglwys that the beaches look white -- made up of thousands of lovely quartz pebbles and boulders.

chris johnson said...

Thanks for the invitation. Next time I won't be shy. Today it is raining again and misty so not good for excursions

I did see a pile of stones and wondered whether it was "yours", but the lane widening was a different case. Someone is taking out one of the "walls" to widen the lane it seems