CN413

Diffwys Quarry  

29/07/2020  

Designated  

Gwynedd  

Ffestiniog  

270914  

346057  

Industrial  

Quarry  

Post Medieval/Modern  

The monument comprises the best-preserved remains of Diffwys (Casson) Quarry, located immediately north east of the town of Blaenau Ffestiniog. Opening in the 1760s Diffwys was the first formalised quarry in Ffestiniog and was known as "mam-chwarel" (mother quarry). The quarry’s origins were as dispersed pit workings on the higher ground to the east, later development taking the form of a series of working levels further west along with some underground mining. At its peak between the 1820s and 1880s Diffwys Quarry provided employment for over 200 men producing an output of 5000 tons of slate per annum. Diffwys was the first quarry to export slates to markets beyond the North Wales region. Originally utilising sledgeways and packhorses to transport material for shipment on the Dwyryd (see ME108 - Cei Tyddyn Isa) the quarry developed a cart road in 1801. Whilst the quarry pioneered the use of internal tramways it was reluctant to embrace the wider rail transport network, in part because of the use of different gauge rails, but eventually constructed a direct incline to the Ffestiniog Railway in 1863. A system of impressive inclines continues to connect the town with the quarry today. The western part of Diffwys retains three substantial inclines – the largest of which is almost 300m in length – designed to transport material through the quarry to the Ffestiniog Railway. Smaller, subsidiary inclines used to move material between levels are also well-preserved, as are the remains of at least 12 winder-houses. All of the winder-houses are relict structures although some retain drum, brake or other gear still in situ. A variety of designs and sizes of winder-house have been preserved, some with associated tramways and weigh houses. The prominent 'Floor 6' steam-powered integrated mill is the largest building at Diffwys and the best surviving example of its type. A well-preserved relict mill, it is roofless but retains all of its walls to full height. Originally built in the early 1860s the mill is orientated broadly E-W and is 15m wide but almost 100m long, having been extended twice. The mill utilised unique guillotine-type trimming machines to reduce slate blocks to produce roofing slate. Whilst the machinery was generally removed when the mill ceased operation, at least 16 machine bases survive internally. Externally, railway tracks and wagons are evident. 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. Diffwys retains evidence of each stage of the quarrying process including a highly developed transport system. The quarry was intensively developed during the 18th and 19th centuries leaving a wide variety of well-integrated features, many retaining evident phasing or stratigraphic relationships. As levels of activity were low from the 1880s until its closure the quarry survives in a well-preserved, coherent state. The quarry is a rare survival as an extensive fossilised landscape within a wider context of active mineral extraction. The scheduled area is one large polygon comprising the remains described and an area around them within which related evidence may be expected to survive. It includes the relict slate mills, tramways, inclines, engine-houses, smithies, chimneys, offices, weigh houses and areas of slate waste tipping. The irregular polygon is approximately 550m N-S by 980m transversely and is centred on NGR 270914, 346057.