William Southern Clark, C.E., F.G.S., (1818–1864), was appointed chief mineral agent to the Marquis of Bute in 1845, and lived at Mardy House, Aberdare, from 1854 when the house was built. Clark was born in 1818 in Wallsend, Northumberland; married Susan Haliburton in Brampton, Cumberland, 1848; and died, after a protracted illness, a relatively young man at The Mardy, Aberdare on 17th May 1864. He was succeeded by his assistant, William Thomas Lewis, (who became Lord Merthyr).

Mardy House remained the centre of Bute mineral affairs until the nationalisation of coal reserves in 1938.