Rhyd y Sarn slate mill was located on the south bank of the Afon Dwyryd, at its confluence with the Afon Goedol. It was an example of a 'remote' mill, processing material imported from the Diffwys Casson quarry (NPRN 416213) some 4.5 kilometres to the north-east. It is believed that before 1802 slate was sawn here in a water-powered sawmill, and was the site of early circular sawing experiments using a horse whim. This may also be the origin of the Swsana Pierce gravestone of 1805 (Llan Ffestiniog), one of the earliest bearing circular sawmarks. The building was later re-used as a tannery. The wheelpit and leat were still visible in 1991.
Source:
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), p.108-9.
Ordnance Survey County Series 25-inch map: sheet Merionethshire XII.1, edition of 1889.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.140.

David Leighton, RCAHMW, 17 June 2015