The South Wales Coalfield extends across parts of Pembrokeshire, Carmarthenshire, Swansea, Neath Port Talbot, Bridgend, Rhondda Cynon Taf, Merthyr Tydfil, Caerphilly, Blaenau Gwent and Torfaen [REF].
It comprises a fully exposed synclinorium with a varying thickness of Coal Measures (Upper Carboniferous / Pennsylvanian) deposits with thick, workable seams in the lower parts and generally thinner and sparser seams in the upper parts, together with a development of sandstones (Pennant Sandstone).