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Wednesday, 24 August 2016

Gelli-fawr morainic debris

I have been trying to track down the precise location of the "source area" for all those massive stones which have been used in the landscaping of the new visitor centre at Tafarn y Bwlch.   A successful mission.  They have all come from the uncultivated fields above the Gelli-fawr hotel, mostly upslope of a little shale quarry (used for roadstone) at grid ref SN065347.   The altitude is c 240m.  Thousands of tonnes of mostly dolerite boulders have been taken from here, with a double purpose as planned by landowner Llew Rees: he has helped to clear the land of large stones here, while creating some very effective landscaping at Tafarn y Bwlch.

The landscape features in the fields around the quarry are very subtle, but there are traces of elongated morainic ridges that might be associated with an ice edge.  The face of the quarry is interesting:


W can see that the top 3m of the shale bedrock is broken and shattered, and that the strata have been "bent over" by slope processes over a great length if time.  This is one of the most spectacular examples of downslope broken rock transport I have seen in a long time. 

If you look carefully, you can see that there are erratic boulders embedded in the upper layers of these slope deposits.  This is the base of an overlying layer, about 4m thick, of stony and gravelly till packed full of abraded and faceted boulders of all shapes and sizes.  Nearly all of them are made of locally derived dolerite.

Above the quarry Llew has now made a depot of stones which may still be intended for Tafarn y Bwlch.  A very nice collection of glacially shaped boulders -- they could easily have come from Stonehenge!


This is interesting, since the obvious occurrence of glacial deposits here matches with the observations I have made from elsewhere in the vicinity -- for example at Cilgwyn, Gernos Fawr and Tafarn y Bwlch.  It's quite possible that ice lobes pushed into the col occupied by Gernos Fawr smallholding from both the west and the east.  Watch this space for further developments.....



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