Dorothea quarry

Dorothea

A flooded pit in the quarry in July 2010
Location
Dorothea Location in Gwynedd
Location	near Talysarn
County	Carnarvonshire (now Gwynedd)
Country	Wales
Coordinates	53°1′30″N4°17′0″W / 53.02500°N 4.28333°W / 53.02500; -4.28333 SH 518 503
Production
Products	Slate
Type	Quarry
History
Opened	1820s
Closed	1970 (1970)

Dorothea quarry is a disused slate quarry in the Nantlle Valley area in North Wales. It covers a large area near the village of Talysarn 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 (££199,239.26 in 2025). ^[1] 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. ^[2]

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 (£311,442.43 in Aug 25). ^[3] 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. ^[2]

Production peaked in 1872 at 17,442 tons, ^[4] though 1875 was the most profitable year, generating £14,738 (£1,483,175.72 in 2025). ^{[5] [2]} 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. ^[4]

After closure

Since quarrying ended in 1970, the Dorothea quarry was flooded and become a popular site for scuba diving, even though there were no facilities provided and the landowner did not officially approve the activity. The unregulated nature and depth of the site encouraged some divers to overestimate their capabilities, and in the decade 1994–2004, 21 divers lost their lives in the quarry. ^[6] The British Sub Aqua Club advised members not to dive there ^[7] for many years.

Diving was eventually resumed in 2021, under license from the landowner, through the North Wales Technical Divers club. ^[8] The quarry is extremely deep (over 100m) and requires a high standard of diver training. As such access is strictly limited to those with appropriate qualifications.

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. ^[4] This was the last new Cornish engine to be built. ^[i] It remains in situ in its Grade I listed engine house. ^[9]

Transport

The quarry was one of the first users of the 3 ft 6 in (1,067 mm) Nantlle Railway in 1828. It later developed an extensive internal tramway system of 2 ft (610 mm) gauge. Dorothea was one of the first users of De Winton locomotives in 1869. ^[4]

Locomotives

2 ft (610 mm) gauge locomotives known to have worked at Dorothea.

Name	Builder	Works No.	Date built	Type	Notes
[10]	De Winton		c1869	0-4-0 VB	Scrapped by 1914
Glyn [10]	De Winton		1874	0-4-0 VB	Scrapped by 1914
Dorothea	Hunslet	763	1901	0-4-0 ST	Worked until 1942. Now preserved on the Launceston Steam Railway [11]
Wendy	W.G. Bagnall	2091	1919	0-4-0 ST	Purchased from the Votty & Bowydd Quarry in Blaenau Ffestiniog in 1930. Preserved by the Hampshire Narrow Gauge Railway Trust [12] and donated by them to the Statfold Barn Railway
[10]	Deutz		1926	4w PM	Purchased from the Votty & Bowydd quarry in March 1930. Believed scrapped.
[10]	Lister	33527		4w PM	Out of use in October 1960. Scrapped in 1964.
[10]	Lister	3916		4w PM	ex-Tarmac Limited contract in Wolverhampton. Out of use by 1964.
[10]	Lister	3950		4w PM	ex-Tarmac Limited contract in Wolverhampton. Out of use by October 1960. Scrapped in 1964.

References

1. Another engine was installed later at Hodbarrow Mine, Cumberland, but this was an older engine, re-located.

1. Bank of England, "Inflation calculator", Bank of England. Last updated 17 September 2025. Retrieved 12 October 2025.
2. Lindsay, Jean (1974). A history of the North Wales slate industry. David & Charles.
3. Bank of England, "Inflation calculator", Bank of England. Last updated 17 September 2025. Retrieved 12 October 2025.
4. Richards, Alun John. The Slate Regions of North and Mid Wales. pp. 70–71.
5. Bank of England, "Inflation calculator", Bank of England. Last updated 17 September 2025. Retrieved 12 October 2025.
6. "Why Dorothea claims lives". North-west Wales News. BBC Online. 22 March 2004. Retrieved 16 March 2007.
7. "Dorothea quarry death: British Sub Aqua Club urges divers to stay away from site that has witnessed 25 deaths". Wales Online. Media Wals Ltd. 1 September 2014. Retrieved 3 June 2025.
8. "Explore 16 Remarkable UK Inland Diving Sites: Coldwater Adventures". Divernet. Rork Media Limited. 20 February 2021. Retrieved 3 June 2025.
9. "Cornish Beam engine, Dorothea Quarry, Dyffryn Nantlle". The Slate Industry of North and Mid Wales. Retrieved 21 February 2019.
10. Tonks, Eric S. (1968). Industrial and independent locomotives and railways of North Wales. The Birmingham Locomotive Club.
11. "Dorothea". Launceston Steam Railway. Archived from the original on 8 November 2014.
12. "Dorothea Slate Quarry". The Narrow Gauge Railway Museum.