CN425

Cwmorthin slate quarry, mine, railway and ancillary features  

24/06/2021  

Designated  

Gwynedd  

Ffestiniog  

268194  

346423  

Industrial  

Quarry  

Industrial  

The monument comprises the remains of Cwmorthin Quarry, a substantial underground slate mine and quarry landform located west of Blaenau Ffestiniog between Cwmorthin and the village of Tanygrisiau along with its surface buildings, inclined planes, waste tips and quarry railway. The quarry is located between Oakeley Quarry (CN422) to the north and Wrysgan Quarry (CN423) to the south. It is the largest relict quarry of its type in the region. Cwmorthin was established in 1810 as an open quarry but became an underground operation during the 1860s following the construction of the Cwmorthin connection to the Ffestiniog Railway. In 1882 the quarry employed more than 500 men and utilised 3 mills containing 50 saws and 50 dressing machines in total. In 1900 the quarry was absorbed into the neighbouring Oakeley Quarry but the two inclines of the Cwmorthin Quarry Railway remained in use until 1902. The underground operations continued to be worked until 1939 while some surface reworking continued into the 1980s. The designated area is divided into three parts: Cwmorthin Slate Mine and the North Processing Area (Area A), Cwmorthin Terrace, Capel Tiberias and West Tips (Area B) and the South Tips, Quarry Inclines and Quarry Railway (Area C). Area A: Cwmorthin Slate Mine and the North Processing Area. The east half of Area A comprises the known extent of the underground slate mine - laid out across 12 floors exploiting the Old and Back veins in the Ordovician formation. During operation the mine was kept free of water by active pumping and drainage but today much of the mine is flooded or has suffered collapse with only Floors A – E still accessible. The mine floors and the chambers worked off them remain exceptionally well preserved having seen little disturbance by modern quarrying activity. Slate slab steps and inclines connect many of the workings and include an unusual single-track incline connecting the lake level to Floor E known as the Back Vein Incline. Floor E also retains a wealth of artefactual survival including numerous waggons, a compressor with extant cooling tanks, in situ winding drums and a unique crane-type pulley support. Above ground, Area A includes a number of short inclines emerging from the underground workings, some with engine winding houses at their head. At the toe of the inclines is evidence of hand finishing in the form of gwaliau surrounded by piles of fine slate waste. The foundations of the Lake Mill survive alongside Cwmorthin House, the manager’s house and garden and other ancillary buildings associated with the quarry and railway. The distinctive slate waste fingertips that extend into the lake define the west boundary of Area A and the railway formation defines the southern extent. Area B: Cwmorthin Terrace, Capel Tiberias and West Tips. At the south end of the lake, Area B includes the main quarry barracks, also known as Cwmorthin Terrace or Tai Llyn. This impressive row of relict cottages retains small outbuildings to the rear and gardens facing on to the lake to the north. It is two-phase construction – the western end built from country stone and the east built from slate block. The remains of the independent chapel are located 60m northwest of the barracks while a tip and relict incline form the southern extent of Area B. Area C: South Tips, Quarry Inclines and Quarry Railway. The slate waste tips in Area C cover the southern slopes of Craig Nyth y Gigfran and their form today is as illustrated on the Ordnance Survey First Edition Map (1888). The Cwmorthin Quarry Railway formation is a well-preserved cutting, sometimes rock-cut and elsewhere utilising buttressed embankments. The railway system retains two relict counterbalance inclined planes – the upper, Tai Muriau Incline and the lower, Village Incline which passes beneath the minor road to Dolrhedyn. Both winder houses survive as well as some sleepers and cables. The monument is of national importance as a well preserved relic of the slate quarry industry and for its potential to enhance our understanding of the industry. The underground workings are extensive and given the exceptional levels of preservation in the accessible areas, the currently inaccessible floors are expected to retain significant archaeological potential. The relict surface remains at Cwmorthin Quarry survive much as they would have appeared at the end of the 19th century, the quarry preserving several important landscape-scale features. The scheduled area comprises the remains described and an area around them within which related evidence may be expected to survive. The scheduled area is divided into 3 parts: Area A is a large irregular polygon c.900m N-S by c.750m transversely and centred on NGR 268194, 346423. Its eastern half is defined by the known extent of underground workings while the west is defined by the visible edges of extant historic tips. Area B is centred on NGR 267924, 345875 and is an irregular polygon c.300m NW-SE by c.30m transversely with an additional 6m square polygon located 60m NW of the main polygon to include Capel Tiberias. Area C is centred on NGR 268258, 345703 and is a large irregular polygon c.580m N-S by c.400m transversely with the linear railway extending a further 650m from the SE boundary.