Geograph - photograph every grid square

The rocks in the hills north of the Afon Dyfi belong to the Llandovery group, the oldest part of the Silurian period. The section shown here, which is about 4m high and part of a small rockface by the side of the steep track into Esgaireira forest, appears to be metamorphic rock. The rock splits into thin, almost vertical layers, while wider coloured bands can be seen at an angle of about 30 degrees with the vertical. This occurs when sedimentary rock containing small orientated crystals is folded under pressure. The crystals align perpendicular to the applied stress, resulting in cleavage planes between them. The original bedding, i.e. the pre-metamorphic sedimentary layers, remain identifiable as bands intersecting the cleavage planes.