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Saturday, 28 April 2012

Cambrian sandstone erratics on Carningli?

This has got me seriously flummoxed.  On a walk on the side of Carningli today , I found these two erratics.  (Robert, note that I do not say "glacial erratics")  They were in an area of a field where a neighbour is levelling out the ground.  These erratics were among many others of all shapes and sizes.  The one of on the right here is about the size of a human skull.  There's a lot of old building rubble in the vicinity, including bits of slate and old mortar -- so I think there may have been a building somewhere nearby, at some stage.

Both of these -- the smaller reddish pink one and the larger purple one -- look remarkably like the Cambrian sandstones around Caerfai and Caerbwdi near St David's. Shall we assume that the stones in question were incorporated into a cottage at some stage?   Nobody who puts up buildings in this area -- whether in the 1700s or today -- carries lumps of stone this size from St David's to the flanks of Carningli.  There is quite enough in the way of building material in the vicinity as it is.  Moraine and fluvioglacial material all over the place.

But for the ice to have carried this material from St David's to Carningli, it would have been travelling from the SW towards the NE -- I have never seen any evidence to support the idea that the ice has ever travelled in that direction.  Ordovician conglomerates incorporating Cambrian sandstone cobbles and boulders?  As far as I know, there are no such things in the Newport area.

The only thing I can think of is that there might be outcrops of Cambrian sandstones somewhere out in Cardigan Bay or St George's Channel -- and that these sea-bed outcrops might be the places from which these erratics have been plucked by over-riding ice.

Are there any rocks with this colour and texture in the Cambrian of North Wales?  I don't know that area well enough.   Ireland, maybe?


Anonymous said...

"Nobody...........carries lumps of rock this size from St David's to the flanks of Carningli".

Pterodactyls during the Jurrasic??
[Lateral and very imaginative thinking]

Professor Challenger

BRIAN JOHN said...

Thanks, Professor. As I have already speculated in a private message to an esteemed colleague, I cannot be sure that there was a Lost World here, populated by exotic creatures. One remote possibility is that sandstones from Porthclais (near St Davids) have come in to the port of Newport (Parrog) as ballast in a ship. So they might then have been dumped onto the sands in the estuary. but that;'s a VERY long shot -- and why would a farmer cart some medium-sized red boulders from the beach, all the way up to the flanks of Carningli, just to build them into the rubble wall of a cow shed or other simple building, when there are far too many small boulders lying about all over the place anyway, needing to be cleared from the land? Doesn't make sense to me...

What makes more sense id]=s that they might be Devonian, from Ireland or North Wales. Investigations must proceed.....