Dorothea quarry
Dorothea quarry is a large slate quarry in the Nantlle Valley in North Wales.
The quarry covers a large area around Talysarn and contains three flooded deep lakes within the site.
History
Dorothea commenced working in the early 1820s, though there were a number of smaller workings on or near the site before this. By 1848 it had become the dominant quarry in the area, employing 200 men and producing 5000 tons of finished slate. Production peaked in 1872 at 17442 tons. In the 1930s over 350 men were employed at Dorothea. Production dropped significantly after the start of World War II and the quarry closed in 1970.Since quarrying ended in 1970, the Dorothea quarry has flooded and become a popular site for scuba diving ; 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 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 in 1828. It later developed an extensive internal tramway system of gauge. Dorothea was one of the first users of De Winton locomotives in 1869.Locomotives
gauge locomotives known to have worked at Dorothea.| Name | Builder | Works No. | Date built | Type | Notes |
| Dorothea | Hunslet | 763 | 1901 | Worked until 1942. Now preserved on the Launceston Steam Railway | |
| Wendy | W.G. Bagnall | 2091 | 1919 | Purchased from the Votty & Bowydd Quarry in Blaenau Ffestiniog in 1930. Preserved by the Hampshire Narrow Gauge Railway Trust |