The coal industry in Wales played an important role in the Industrial Revolution in Wales. Coal mining in Wales expanded in the 18th century to provide fuel for the blast furnaces of the iron and copper industries that were expanding in southern Wales. The industry had reached large proportions by the end of that century, and then further expanded to supply steam-coal for the steam vessels that were beginning to trade around the world. The Cardiff Coal Exchange set the world price for steam-coal and Cardiff became a major coal-exporting port. The South Wales Coalfield was at its peak in 1913 and was one of the largest coalfields in the world. It remained the largest coalfield in Britain until 1925. The supply of coal dwindled, and pits closed in spite of a UK-wide strike against closures. Aberpergwm Colliery is the last deep mine in Wales. The South Wales Coalfield was not the only coal mining area of the country. There was a sizeable industry in Flintshire and Denbighshire in northeast Wales, and coal was also mined in Anglesey. Coal mining areas The South Wales Coalfield extends from parts of Pembrokeshire and Carmarthenshire in the west, through Swansea, Llanelli, Neath Port Talbot, Bridgend County Borough, Rhondda Cynon Taf, Merthyr Tydfil, Caerphilly County Borough and Blaenau Gwent to Torfaen in the east. The rocks in this area were laid down in late Carboniferous times. At that time warm seas invaded much of southern and northeastern Wales, and coral reefs flourished and were laid down as limestone deposits. In South Wales particularly, extensive swamps developed where tree-sized clubmosses and ferns grew. The decay of this vegetation as it died formed peat, which was slowly buried under other sediments. The peat was slowly consolidated and converted by the pressure of overlying layers into seams of coal. Although thinner than the original peat layers, some of the coal deposits in South Wales are of great thickness. The North Wales Coalfield is divided into two parts: the Flintshire Coalfield to the north and the nearly contiguous Denbighshire Coalfield to the south. The Flintshire Coalfield extends from the Point of Ayr in the north, through Connah's Quay to Caergwrle in the south. It also extends under the Dee Estuary to the Neston area of the Wirral Peninsula. The Denbighshire Coalfield extends from near Caergwrle in the north, to Wrexham, Ruabon, Rhosllannerchrugog and Chirk in the south, a