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Sunday, 1 September 2013

Rocks from Tycanol Wood and Nevern Estuary -- is there a match?

 The strange erratic (one of several) lying on the surface of eroded till in the Nevern Estuary

A fragment from one of these erratics in the Nevern Estuary

I have just had a sudden thought in relation  to this post:
and the help given by Rob in determining what this rock might be and where it might have come from.

Rob kindly said this about it, having looked at the sample:
The strange rock found on the shore of the estuary, across the river from the Parrog, Newport. Felsite, maybe from North Wales?  Not certain. Siliceous igneous rock with feldspar megacrysts and a sub-spheroidal fabric. Crystal tuff??  

  I have had an inspiration that it looks very similar to the rocks outcropping in the highest part of Tycanol Wood, beneath the tors of Carnedd Meibion Owen.  Here is one of my photos from that site:

 Outcrop on the highest tor in Tycanol Wood, not far from Newport, Pembs.

There do seem to be similarities in colour, texture, and that strange sinuous / knotted / gnarled surface texture as well.  There are a lot of strange rocks between Carnedd Meibion Owen and Newport on the coast -- and maybe other outcrops of something similar. 

I accept Rob's point that you can't do any sensible petrology from photos, so all we can do is speculate in an amateurish sort of way.  Crystal tuff?  Felsite?  Richard Bevins knows the rocks from this area very well -- Richard, if you see this, any comments please?

PS.  Message from Rob: he suggests that Richard is of the view that this might be a microtonalite.  Or maybe several microtonalites -- can't say whether they come from the same outcrop, obviously, without very detailed analysis.........

See also:

By the way, has anybody yet identified that strange erratic called the Trefael Stone?


Myris of Alexandria said...

The Trefael capstone has been described but it is not in the public domain/in press.
It is an altered crystal-lithics tuff probably part of the Fishguard Volcanics and does not match anything found at Stonehenge. The data belong to George Nash.
Reports that it is spotted dolerite in the archy press earlier this year and linked to Dr Ixer's name were a surprise to him.
He is correct photo identification
of rocks is like cooking and eating random wild fungi it is only a matter of time before the Grim Reaper pulls up a chair.
The recent rocks look like your erratic #1 from way back. That is thought to be microtonalite
Spotted rhyolite is a new term that is not to be encouraged.

BRIAN JOHN said...

Thanks Myris -- all good useful info. Spotted rhyolite? Always good to do a bit of stirring.......

TonyH said...

Passed by Tycanol Wood after visiting Pentre Ifan cromlech for the first time with my brother last week. Sorry not to have dropped in to see you, Brian. Maybe next year.

Was quite close to Castell Mawr but couldn't see it from the Newport - Cardigan road. Any sightings of our intrepid archaeologists yet?

BRIAN JOHN said...

Thanks Tony

Castell Mawr is very difficult to see from anywhere -- except from the air! I have heard nothing from anywhere about this year's dig. Been rather busy myself, so I have no idea whether the diggers are at Rhosyfelin, or at Castell Mawr, or at both...... news will filter through eventually, I dare say.......

Dave Maynard said...

MPP seems to be in the district. This shows he is due to give a talk at Moylegrove on the 18th of this month. I might go along if I'm not on my travels elswhere.