Moel Fferna slate mine is located at the head of the valley of Nant Pandy, a tributary of the Dee at Glyndyfrdwy. This high altitude site (500m) opened in the 1870s. It was a substantial producer of roofing slate almost entirely won from underground working.

Adits were on seven levels, with a large steam (later internal combustion) powered mill. A gas engine was installed in 1912, and in 1923 an oil-engined electricity generator was installed to power saws. This was the first Welsh quarry to introduce, in 1926, high-speed circular saws using blades coated with industrial diamonds or carborundum.

After 1872 a trwnc (table) incline, originally only up to level 3, was extended as additional levels were opened. This incline connected the levels and also lowered finished product to the Deeside Tramway. This was extended southwards - in conventional steel track - to serve this site (also passing through the nearby Deeside slab quarry, NPRN 308670). Wagons travelled down under gravity, controlled by a riding brakeman, empties returned daily by horse. In 1898 184 men were employed, in 1937-8 100. The mine closed in 1960.

In the 1990s visible remains were extensive at various levels - adits, buildings (including weigh-houses, offices, a type of drum house which housed horizontal sheave gear, a powder house, dressing sheds) and a large stockyard near the mill.  The mill is unusually constructed with fairly crude walling and a corrugated iron roof.  Along one side is a lean-to with sloping walls and limited access to the mill itself, and at one end of the mill is the massive concrete base for the oil engine. Two massive pillars which supported the gantry for transferring wagons between the different gauges used on the surface (2ft 6 inch) and below ground (2 ft/25 inch).

Underground there is much chambering on several levels, though access is difficult, with remains of a bridge across workings and gravity inclines which retain rollers and drums, but no rails.  On level 6 there is a large wooden cog supporting the chamber roof, a technique usually used in coal mining.

Sources:
Correspondence 2022-3

D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015), p.117-8.
Ordnance Survey County Series 25-inch maps: sheet Denbighshire XXXIII.16, editions of 1875 and 1901.
RCAHMW air photos, AP955026/46-9; 95-CS-0237.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.203-4.

A.J.Richards, The Slate Regions of North and Mid Wales and their Railways (1999), p.242-3