Welsh Slate: Berwyn (N4 N5) Portmadoc (N6 N7)
Reference N4 N5 N6 N7 NAME Berwyn (honed) Berwyn (riven) Portmadoc (honed) Portmadoc (riven) TYPE Slate Slate Slate Slate GEOLOGY Silurian. Ludlow Beds Silurian. Ludlow Beds Ordovician. Llandeilo Series Ordovician. Llandeilo Series COUNTY Clywd Clywd Gwynedd Gwynedd COLOUR Deep blue Deep blue Blue/grey. Occasional pyrite flecks Blue/grey. Occasional pyrite flecks TEXTURE Extremely fine grained….