 At the large and very profitable Dinorwic Quarry in Llanberis, in 1870, De Winton's built and equipped an entire workshop with machinery powered by overhead shafting that in its turn was driven by the largest water wheel in the United Kingdom (over 50 feet in diameter), which remained in daily use until 1925 when it was replaced by a Pelton wheel but retained as standby.The wheel is the subject of a preservation order but in fact the entire workshop complex is preserved as the National Slate Museum.Jeffreys Parry de Winton (born Wilkins 1828–1892) was mayor of Caernarfon (1870–1872) when his company was one of the rising enterprises in the town.