Dinorwic Slate Quarry, North Wales

Dinorwic (sometimes Dinorwig) Slate Quarry is a large former slate quarry located in North Wales  located between the villages of Llanberis and Dinorwic in Wales that saw operation between 1787 and 1969. At its height at the turn of the century, it was the second largest slate quarry in Wales, and the world, after the neighboring Penrhyn quarry near Bethesda. During its peak it exployed close to 3000 mean and produced 100,000 tonnes of slate a year. Dinorwic covered approximately 700 acres and consisted of two main quarry sections, with 20 galleries in each. An extensive internal tramway system connected the quarries and used transporter inclines to transport the slate between the galleries and to the workshops. Since its closure in 1969, the quarry has become the site of the National Slate Museum, a regular film location, and a rock climbing destination.

The quarry was first opened in 1787 by the Welsh industrialist, Thomas Assheton Smith, who also owned the Nantlle Valley slate quarries took over the small workings there. The slate from Dinorwic was of a particularly high quality and quickly gained a reputation for excellence. The first incline was built in 1789, but sledge operations to move the quarried slate continued until 1816; after which all downhill movement was by way of self acting inclines. Eventually, two main inclines were constructed in the quarry, with tramway systems following in the 1830s with approximately 50 miles of tramway being installed during the height of its operation. By the mid-19th century, the quarry had become one of the largest in the world, employing over 3,000 workers. Several blondins were installed in the 1930s to facilitate movement of slate from the deepening pits.

The slate vein at Dinorwic is nearly vertical and lies at or near the surface of the mountain, allowing it to be worked easily from a series of stepped galleries. This is however not quite how the quarry developed. The first quarrying operations are Dinorwic were spread across several sites: Adelaide, Allt Ddu, Braich, Bryn Glas, Bryn Llys, Chwarel Fawr, Ellis, Garrett, Harriet, Matilda, Morgan’s, Raven Rock, Sofia, Turner, Victoria, and Wellington. This was a situation that lasted for many years, certainly until the mid-1830s. Innovation was important, and in 1825, the quarry’s first railroad (Dinorwic Railway) was opened and ran to the companies port on the Menai Strait, inspired by Penrhyn Quarry’s 1801 tramway. Produce from the upper quarries was able to use this railroad easily, but Wellington, Ellis, Turner, Harriet, and Victoria quarries were all below the level of the railway. This problem was solved in the 1840s when a far more sophisticated railway was opened (Padarn Railway), running along the shore of Llyn Padarn. This was the first of the slate quarry railways to use steam locomotives. The original Dinorwic Railway was removed by the 1850s as it was uneconomical to operate and suffered from limited capacity. 

These developments saw the quarry as we know it take shape. Adelaide quarry became a part of Allt Ddu, and Chwarel Fawr and Chwarel Goch became linked to it too. In the ‘Great New Quarry’, Raven Rock and Garret Quarries became one massive quarry, operating as an open hillside gallery quarry, with the lowest two levels being accessed by tunnels. Harriet, Morgans, and Sofia quarry are all still identifiable as separate pits today, whilst Braich quarry became a large working of three contiguous smaller pits. Below this, The galleries of Victoria and Wellington were joined along the hillside and continued downwards in two separate main workings: Wellington and Hafod Owen. Each was eventually to contain several small sinks too, some below lake level. The current form of the quarry is little different from that of the time of the Great War, save for enlarging of the actual quarry faces and deepening of the sinks. Certainly, all the main inclines were in place, very little was altered until closure. Processing of the quarried slate was undertaken at a number of mill buildings located throughout the quarry. The main Mill (Ardal Mills) sat to the west of the workings, with two further mills located at the Wellington Level (demolished to make way from the Dinorwic Power Station) and Australia Level. 

Dinorwic Quarry closed abruptly in 1969. This was a result of declining output and difficulty in extracting slate due to the precarious nature of the tips; in 1966 a large slide in the Garret area all but halted production. A small clean up operation was undertaken using modern mining equipment, but the recovered slate was less than that produce by the traditional method the previous year. An public auction was arranged to recover some costs and reduce the quarries debts; before bidding start it was announced that Gwynedd County Council had placed a Preservation Order on the Gilfach Ddu workshops, and many items within it. These workshops now form the National Slate Museum (well worth the visit if you are in the area). Since the closure of the Quarry, the CEGB built a pumped storage hydroelectric power station (Electric Mountain) beneath the quarry; aside from some work in the Wellington area this has ensured the survival of the rest of the site. It remains in remarkable condition, with many of the buildings and artifacts remaining in place. 


Modified: 11th May 2023