The now disused Gorseddau Slate Quarry was first opened 1807, as a small concern, but its main period of working was between 1854 and 1857 when it was developed by the Bavarian mining engineer Henry Tobias Tschudy von Ulster. The quarry was a complete commercial failure. Despite massive capitalisation and investment in milling, water courses and reservoir, workers' housing and railway to Porthmadog, returns were derisory. By 1859, its 200 men were producing less than 1400 tons per annum - seven tons per man year. Output peaked at 2140 tons in 1860. The quarry closed in 1867, possibly with some later sporadic working.
The visible remains include tiered workings and waste tips set into and against a south-west facing hillside. There are remains of an incline and several ruined structures including: the Gorseddau Tramway (NPRN 34663) that was built to connect the quarry with Porthmadog, Ynys-y-Pandy Mill (NPRN 40572) and Treforys Workers Village (NPRN 306319).
D.Gwyn, Welsh Slate: the Archaeology and History of an Industry (RCAHMW 2015).
David Gwyn & Merfyn Williams (1996) ‘A Guide to the Industrial Archaeology of North West Wales’. Association for Industrial Archaeology.
A.J.Richards, A Gazeteer of the Welsh Slate Industry (1991), p.98-9.
David Leighton & J.Wiles, RCAHMW, 11 February 2015