Cwm Cerwyn, Preseli

 

 

Thanks to Hugh360 for this excellent image of Cwm Cerwyn, seen from the upland ridge near Cerrig Marchogion. If you ignore that traces of man-made quarrying, you can see clearly that this is an incipient cwm or cirque, never fully developed but nonetheless showing signs of active ice here.  I think the mound which is visible just left of centre is made of bedrock, but it will reward further research......

I know there is a till sheet here, but I have never managed to discover the till thickness. I am not sure whether we can refer to a real terminal moraine marking the edge of a small glacier........

The last glacier here might have been in the Younger Dryas (Zone III).   But in this location, on the margin of glaciation, I can envisage a small glacier coming and going on many occasions during the Quaternary.