A steam powered stone-built slate mill situated on Floor 0 of Diffwys quarry, dating from the mid/late 19th century. Part of the housing for the steam engine and chimney to exhaust the steam engine survive at the southern end of the building. To the north of this the outline of the mill be traced suggesting a building around 42m in length and 23m in width.

Louise Barker, RCAHMW, October 2015