Cwmystradllyn and Cwm Pennant is a quarry landscape that dates from the confident years of the 1850s to the 1870s, when the small workings at Gorseddau and Bwlch y Ddwy Elor were opened out on a similar principle to Penrhyn quarry – stepped galleries with incline access – and were provided with railway access to the sea at Porthmadog.
Gorseddau quarry in Cwmstradllyn had been worked on a small scale since 1836 but was actively developed from 1854. An ambitious multi-storey water-powered off-site slate-slab mill, Tŷ Mawr Ynysypandy was constructed, on the pattern of a foundry but looking more like a ruined abbey church in its mountain setting, and a railway laid to the harbour at Porthmadog.
The railway and probably Tŷ Mawr, were designed by Sir James Brunlees, who was responsible for the Sao Paulo Railway in Brazil, the Mont Cenis Summit Railway, the Mersey Railway and many others, but the mill was erected by the local stone mason, Evan Jones.
A workers’ village, Treforys, markedly ‘highland clearance’ in its plan, was also constructed. Operations here were short-lived, as commercially viable rock is very limited. The quarry produced no significant amount of slate after 1866.
A small quarry at Bwlch y Ddwy Elor in nearby Cwm Pennant was worked on a small scale in the 1860s, as the Prince of Wales slate quarry. The manager was William Francis, who formerly ran Penrhyn quarry. Seven galleries were opened out, each connected by a single main incline to a water-powered slab mill at its foot. The mill, completed in 1864, anticipates the design of the slab mills erected at Penrhyn’s Felin Fawr complex two years later. A railway to Porthmadog used part of the trackbed of Brunlees’ Gorsedda railway, but Prince of Wales was no more successful than Gorseddau, and working effectively ceased in 1886.
Though neither quarry was successful, they survive as powerful relict landscapes. Both quarries are examples of evolving mid-19th century slate-quarrying practice, with an emphasis on engineered solutions and significant levels of investment even in so wild and remote a setting.