Gwna Group Melange at Porth Wen

 

I couldn't help noticing these amazing rocks next to the brickworks at Porth Wen. I took it for a conglomerate although the embedded fragments are very angular which would suggest that they had not been transported very far. They also seem to span many layers in the rock, which is odd because it would suggest that they would span more than one age surely. But also, the layers seem metamorphosed like slate. It looks to me like these rocks belong to the Gwna Group and are called a melange, a term I've haven't come across before in geology. It seems that the cause was a vast underwater slide caused by an earthquake which resulted in rock fragments being mixed with mud. See also this excellent site about Anglesey geology.