Sarn slate mill is a two-storey building located on the south bank of the Afom Marchlyn-bach. It probably dates from the 1880s and was a mill used for processing raw material into slates for school use. The waterwheel is in an enclosed wheel pit in approximately the centre of the building. It is approximately 30 feet (9.2 metres) in diameter, is said to be dated 1885, and was supplied by the De Winton foundry at Caernarfon. The exterior of the building is grey brown stone with red-brick dressings and a slate roof.
Source:-
Extract from Cadw listed building description.

RCAHMW, 17 June 2015