[ 73 ] and along with Dinorwic Quarry , it dominated the Welsh slate trade. Although slate quarrying has been described as 'the most Welsh of Welsh industries', [ 74 ] it is coal mining which has become the single industry synonymous with Wales and its people. Initially, coal seams were exploited to provide energy for local metal industries but, with the opening of canal systems and later the railways, Welsh coal mining saw a boom in its demand. As the south Wales coalfield was exploited, mainly in the upland valleys around Aberdare and later the Rhondda , the ports of Swansea, Cardiff and later Penarth, grew into world exporters of coal and, with them, came a population boom. By its height in 1913, Wales was producing almost 61 million tons of coal. As well as in South Wales, there was also a significant coalfield in the north-east of the country, particularly around Wrexham . [ 75 ] As Wales was reliant on the production of capital goods rather than consumer goods, it possessed few of the skilled craftspeople and artisans found in the workshops of Birmingham or Sheffield in England and had few factories producing finished goods – a key feature of most regions associated with the Industrial Revolution. [ 72 ] However, there is increasing support that the industrial revolution was reliant on harnessing the energy and materials provided by Wales and, in that sense, Wales was of central importance. [ 72 ] Modern Wales Historian Kenneth Morgan