Cwmorthin Quarry
| Cwmorthin Quarry | |
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View of Cwmorthin Quarry across Llyn Cwmothin
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 Cwmorthin Quarry
 Cwmorthin Quarry shown within Gwynedd |
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| OS grid reference | SH680459 |
| Coordinates | 52°59′39″N 3°58′02″W / 52.9942°N 3.9671°WCoordinates: 52°59′39″N 3°58′02″W / 52.9942°N 3.9671°W |
Cwmorthin Quarry is a slate quarry west of the village of Tanygrisiau, north Wales. Quarrying on the site started in 1810. In 1860 it was connected to the Ffestiniog Railway. In 1900 it was acquired by the nearby Oakeley Quarry and the two were connected underground. In 1970 it closed along with Oakeley. There was small scale working in the 1980s and 1990s, the mine finally closed in 1997.
Slate extraction began at Cwmorthin in 1810, when a small quarry was opened on the site by the Casson family who were also working the Diphwys Casson Quarry, further to the east. Two of the five Blaenau Ffestiniog slate veins outcropped near where the quarry started, and it is not known whether the early workings were on the Old Vein or the Back Vein, as all evidence has been destroyed by later workings. The veins sloped downwards at angles of between 20 and 45 degrees, and to avoid the expense of removing large volumes of the overlying rock, the quarry soon became a mine, as the chambers followed the vein below ground. This early quarrying lasted for about twenty years, but had ceased by 1830. In 1840, working began again, when John Edwards and his partner Magnes obtained a lease, which was transferred to W B Chorley from London later that year. Chorley's involvement with the quarry continued until about 1860. He employed Allen Searell (possibly Seale) as an Agent for the quarry in 1844, and correspondence between the two men is held by the library at Bangor University, formerly the University of North Wales. In the late 1850s, Chorley began to lose interest in the enterprise, and Searell moved on to the Hafon y Llan Quarry near Beddgelert.
From about 1859, the quarry appears to have been worked by a group of men under an informal arrangement. They leased a wharf at Porthmadog harbour in 1860, until the Cwmorthin Slate Company was formed in January 1861. This had an authorised capital of £100,000, and the company bought the Cwmorthin Isaf estate and part of Tanygrisiau village on 25 July 1861. Work began on underground mining. At some point, the 1 ft 11 1⁄2 in (597 mm) Cwmorthin Tramway was constructed to connect the quarry with the nearby Ffestiniog Railway at Tanygrisiau. Isherwood states that it was soon after the new company took over in 1861 but Boyd suggests that a survey was carried out in the mid-1840s, and that it was completed in 1850. It was mentioned in the 1850 edition of Cliffe's The Book of North Wales, and the Ffestiniog Railway accounts recorded the first passage of loaded slate wagons down the line in that year. An existing siding at Tanygrisiau, which had served horse-drawn wagons from the quarry, was removed shortly afterwards.
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