South Wales Coalfield

The South Wales Coalfield (Welsh: Maes glo De Cymru) is a large region of south Wales that is rich in coal deposits, especially the South Wales Valleys. It supported a large part, but not all, of the coal industry in Wales.

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.

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). See also the Geology of South Wales. These sandstones have been much used in building construction (including the characteristic terraces of former miners' houses) and give rise to bleak uplands rising 300–600 metres above sea level between the steep-sided valleys in which most deep mines were developed.

The coal generally increases in grade or "rank" from east to west, with bituminous coals in the east, and anthracite in the west, mostly to the north and west of Neath. The Rhondda Valley was particularly known for steam coals which fuelled steamships of the 19th and early 20th centuries.

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