28 July 2021 was a very important day for Gwynedd as this when The Slate Landscape of Northwest Wales was designated as a UNESCO World Heritage Site. The Slate Landscape includes seven specified areas, one of which is the Nantlle Valley Slate Quarry Landscape. The Dorothea Quarry is a feature of this landscape and it is located just 10 minutes from The Woollen Mill.
Welsh slate has been credited with “roofing the 19th century world”. The Dorothea Quarry is a disused slate quarry near Talysarn which provides valuable insight into the slate mining industry. Slate has been mined in North Wales since Roman times. But mining expanded rapidly in the 19th century when the demand for slate increased dramatically during the Industrial Revolution. Work at the quarry began in 1820 and the land was leased by William Turner in 1929. The quarry was originally named Cloddfa Turner. But its name was changed to Dorothea in the 1830s, possibly to honour the wife of landowner Richard Garnons. Work at Dorothea was initially highly profitable but things began to change in the 1840s. The Quarry was put up for sale and subsequently purchased by a group of quarrymen. The group failed to prosper and the Dorothea Quarry was put up for sale again in 1864. No buyer was found. However, John Williams of Denbighshire gradually bought out many of the existing shareholders. By 1879, he had amassed more than 70% of the shares. Production reached its peak in 1872 but dropped significantly at the start of World War II. The quarry was closed in 1970. Since then, the pits have flooded. The Quarry has become a popular site for diving but no facilities are provided. Divers can explore the quarry with the permission of the owner. However, diving is not regulated. This is one of the reasons that more than 20 divers have lost their lives in the quarry since 1994.
There are six pits at Dorothea and they are up to 106m deep. The pits are beneath the water table and so had to be pumped to remain dry. It is possible to see much of the pumping infrastructure at the quarry including what remains of a Cornish beam engine which was installed in 1904. This was the last engine of its type to be built. The engine house in which it is housed is a Grade I listed building (see image below).
The Nantlle Railway was opened in 1828 and gave the quarry a route to the sea. The railway originally ran to Caernarfon, but from 1972 ran to Talysarn where it connected with the national rail network. The railway was used to transport slate until 1959 and was closed by British Rail in 1963.
When the quarry began to expand operations in the 19th century, the village of Talysarn was relocated. Some of the original village buildings can still be seen when you explore Dorothea Quarry, although nature is gradually reclaiming them.
Typically for North Wales, there are no signs directing you to Dorothea and the walking routes at the quarry are not properly waymarked. This situation is extremely frustrating as the various Welsh authorities involved have known that the Slate Landscape could possibly become a World Heritage Site since 2018 but have made no preparations for this eventuality.
The walk around the quarry offers a compelling combination of history and amazing views. It currently receives few visitors and is a great place to explore and walk your dogs.