Dorothea Slate Quarry

The Dorothea Slate Quarry in the Nantlle Valley of Caernarvonshire opened during the 1820s, probably on the site of earlier workings. It was an open pit working. It became the dominant working in the Nantlle area, producing over 5000 tons per annum by 1848. In 1873, its best year, it yielded 17,442 tons. Dorothea employed over 500 men at its peak.

The quarry was almost always profitable although it was beset, like most pit workings, by flooding problems which sapped profits until the1920s. Eight water wheels originally provided power, but these were replaced by steam engines in 1941. Eight chain inclines hauled the slate from the pit until they were replaced by steam blondins across the pit. These were converted to electricity in 1959 and used until 1965. In 1904 a large Cornish engine was installed to pump out flood water from the pit, which was then over 500 feet deep.

The Dorothea Quarry was one of the first users, during the 1860s, of the De Winton steam locomotives built in Caernarvon. It had an extensive rail system both at ground level and on top of the waste banks. The quarry was linked directly to the Nantlle Railway, on which it owned its own wagons, giving it access for exporting its product via Caernarvon. As the Dorothea extended it engulfed the village of Tal-y-Sarn, and the Nantlle Railway had to be re-routed around its northern edge.

The Dorothea Quarry closed in 1970.