Aberllefenni Slate Quarry is one of the oldest running quarries in Wales, possibly dating from the early sixteenth century (in 1500 Plas Aberllefenni was reported to have been roofed using local material). It was worked on an industrial basis from 1810 with the height of extraction in the second half of the nineteenth century after the establishment of the horse-worked Corris, Machynlleth and River Dovey Tramroad (NPRN 43018).

In 1879 the tramroad was converted to steam operation and it became the Corris Railway. The quarry stopped active extraction in 2002, although some surface work continues today. The quarry is currently owned by the Wincilate Group who specialize in high quality slate products.

Slate extracted from the quarry was a very high quality slab, predominantly used in flooring, rather than split for roofing. Evidence of its use can be seen throughout Corris and Aberllefenni not only as masonry material, but in many other forms such as fencing or in place of cast iron for coal-hole covers.

At Aberllefenni, the same narrow vein of slate was worked on both sides of the valley. There were actually three quarries here, Foel Grochan on the north side of the valley and Ceunant Ddu and Hen Gloddfa on the south. The early open workings are high on the hillside, with later underground workings at successively lower levels and the latest at valley floor level. At Foel Grochan, eight near horizontal tunnels (adits) around 45m long and 30m vertically separated, connected to large chambers from which slate was extracted. As more slate was extracted several of the chambers joined vertically, forming an extremely large cavern.

Several features and structures remain of the quarry, some ruined, some still in use. These include a series of inclines and associated drum houses such as that on the north side of the valley that in its final, truncated form was a single-acting table incline with the counterbalance being provided by a rubble filled box. A water-balance incline to transport slate waste (NPRN 275917), a saw mill (NPRN 408514) powered from water of a nearby reservoir and the remains of the quarry office (NPRN 408530) and other ancillary structures.

Louise Barker, RCAHMW, June 2010
Claire Parry, RCAHMW, 14 June 2011

Sources include: Association for Industrial Archaeology: A Guide to the Industrial Archaeology of Mid-Wales, 1984