Abercorris Slate Quarry is shown on the Ordnance Survey County Series (Merioneth. XLII.8 1899) and was recorded during aerial reconnaissance by the RCAHMW on AP94-CS 1791-5 and AP945181/68-70; 945182/41-3. During operation it was amalgamated with Braichgoch Slate Quarry (NPRN 40585) and Gaewern Slate Quarry (NPRN 400831).
The quarry opened in the mid-nineteenth century. It consisted of two hillside workings which developed into pits (up to 1000 ft altitude) accessed by tunnels, with some later underground working. Material was lowered by incline to a mill's area some 600 ft below. The early mill was waterpowered, a later and larger one driven by oil engine. Access was originally by cart track, later direct connection via incline to the Upper Corris Tramway. Output at the turn of the century was about 1000 tons with about 40 men employed. The quarry closed in the 1950s. Surviving remains are extensive though much of the site has been afforested.

Additional sources:
Association for Industrial Archaeology: A Guide to the Industrial Archaeology of Mid-Wales, 1984.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.179.

David Leighton & Claire Parry, RCAHMW, 30 March 2015