Dorothea quarry is a disused

slate quarry The slate industry is the industry related to the extraction and processing of slate. Slate is either quarried from a ''slate quarry'' or reached by tunneling in a ''slate mine''. Common uses for slate include as a roofing material, a flooring ma ...

in the Nantlle Valley area in North

Wales Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...

. It covers a large area near the village of

Talysarn Tal-y-sarn () is a village in the slate quarrying Nantlle Valley in Gwynedd, Wales, next to Penygroes. It is part of the community of Llanllyfni and includes some of Llandwrog. The ward had a population of 1,930 at the 2011 census, the built ...

and contains three flooded deep lakes.

History

Turner family

The quarry commenced working in the early 1820s, though there were a number of smaller workings on or near the site before this. About 1829 it was leased by William Turner who named the workings Cloddfa Turner. In the 1830s the quarry was generating £2000 profits per year (). Turner's son took over as manager and renamed the quarry Dorothea, apparently after the wife of the landowner Richard Garnons. Profits began to fall in the 1840s, and in April 1848 the quarry was put up for sale, with 22 years remaining on the lease.

Local ownership

It was the largest quarry in the area, employing 200 men and producing 5,000-6,000 tons of finished slate a year. A group of quarrymen led by John Robinson, William Owen and John Jones purchased Dorothea from Turner for £3,000 - . They renewed the lease of the quarry in June 1851. The quarry was put up for sale again in 1864, at which time production was given at 1,000 tons per month. No buyer was found, instead John Williams of Denbighshire gradually bought out many of the existing shareholders, and by 1879 he had amassed more than 70% of the shares. Production peaked in 1872 at 17,442 tons, though 1875 was the most profitable year, generating £14,738 (). In the 1930s over 350 men were employed at Dorothea. Production dropped significantly after the start of

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...

and the quarry closed in 1970.

After closure

Since quarrying ended in 1970, the Dorothea quarry has flooded and become a popular site for

scuba diving Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for " Self-Contained Underwater Breathing Apparatus", was coined by Chr ...

(even though there are no facilities provided, and diving is officially banned in the quarry); the unregulated nature and depth of the site has encouraged some divers to overestimate their capabilities – in the decade 1994–2004, 21 divers lost their lives in the quarry.

Description

The quarry sits at the bottom of the wide Nantlle valley and consists of six pits, the deepest dropping 106m from the surface. The slate veins here run vertically, allowing unusually deep vertical pits to be dug. Because the pits fall below the

water table The water table is the upper surface of the zone of saturation. The zone of saturation is where the pores and fractures of the ground are saturated with water. It can also be simply explained as the depth below which the ground is saturated. T ...

they needed to be constantly pumped to stay dry. A Cornish beam engine was installed in 1904 to pump the pits; it stayed in use until 1951 when it was replaced with electric pumps. This was the last new Cornish engine to be built. It remains in situ in its Grade I listed engine house.

Transportation

The quarry was one of the first users of the

Nantlle Railway The Nantlle Railway (or Nantlle Tramway) was a Welsh narrow gauge railway. It was built to carry slate from several slate quarries across the Nantlle Valley to the harbour at Caernarfon for export by sea. The line provided a passenger service ...

in 1828. It later developed an extensive internal tramway system of gauge. Dorothea was one of the first users of

De Winton De Winton & Co (1854–1901) were engineers in Caernarfon, Wales. They built, amongst other things, vertical boilered narrow gauge locomotives for use in Welsh slate mines and other industrial settings. At least six De Winton locomotives have ...

locomotives in 1869.

Locomotives

gauge locomotives known to have worked at Dorothea.

References

{{Recreational dive sites, fresit Slate mines in Gwynedd Diving quarries in the United Kingdom Cornish engines Preserved beam engines Llanllyfni Dyffryn Nantlle