Cymerau Slate Quarry is spread over two locations, North (NPRN 400826) and South (NPRN 400829), both situated in Cwm Ratcoed, on its eastern slopes, to the north of Aberllefenni. The workings were separated by a distance of about a kilometre. A lease of 1863 probably marks the start of workings here. An offshoot of Ratcoed, to the north (NPRN 400827), it remained under the same ownership and management for most of its life.
The workings were underground by a series of adits, material being removed by cart. Later working used a water-powered mill, uphauling from an adjacent adit, and making use of the Ratcoed Tramway. Down valley, some ruins of the mill and wheelpit are still visible (in the early 1990s), along with adits and cottages associated with the workings, still in use. Up valley there are two runs of adits (one open), incline and possible mill site. The reservoir and leat system can still be seen.
Production peaked in 1883 when 762 tons were produced by 29 men. By 1893-4 530 tons were produced by 21 men. The payroll reduced to nil by 1900 but the quarry was worked intermittently after that. By 1936 five men were employed all working above ground. The quarry was officially abandoned in 1949 though some working was reported as recently as 1972.

Sources:
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.184.
A.J.Richards, Slate Quarrying at Corris (1994), pp.91-3.
Ordnance Survey County Series maps: sheet Merioneth. XLIII.1, editions of 1889 & 1900.
Association for Industrial Archaeology: A Guide to the Industrial Archaeology of Mid-Wales, 1984

David Leighton & Claire Parry, RCAHMW, 29 January 2015