 In the 1820s, south Wales alone accounted for 40% of all pig iron manufactured in Britain.In the late 18th century, slate quarrying began to expand rapidly, most notably in north Wales.The Penrhyn Quarry, opened in 1770 by Richard Pennant, was employing 15,000 men by the late 19th century, and along with Dinorwic Quarry, it dominated the Welsh slate trade.