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Gorseddau Slate Quarry

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Map ReferenceSH54NE
Grid ReferenceSH5723245275
Unitary (Local) AuthorityGwynedd
Old CountyCaernarfonshire
Period19th Century


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



A quarry which worked the Portreuddyn slate in the Upper Glanrafon beds of Ordovian age. An as-yet undeveloped quarry at Gorsedda was offered for sale in 1836, but it began to develop in 1854 under the ownership of Robert Gill and John Harris and with the arrival of the German mining engineer Henry Tobias Tschudy von Uster. The quarry was opened out on the gallery system developed at Penrhyn Quarry, whereby a spinal counter-balance incline connected a sequence of terraces from the top of the quarry to the bottom. Each terrace contained a quarry gallery, rubble tips, slate trimming sheds, and trimming waste tips beyond. The quarry was served by its own railway to its magnificent slab mill at Ynys y Pandy (scheduled as Gorseddau Slate Factory CN160) and thence to Porthmadog. It was said of the quarry ‘everything that could facilitate the works was produced, nothing being wanted but the slate vein’. It operated for probably only twelve years, and closed in 1871. The quarry included the remains of the working faces, the incline, a drainage adit, waste tips, barracks, stock yards, railways, slate-makers’ shelters (gwaliau), and blast shelters. A remarkable feature is the so-called ‘wailing wall’ over the course of the Gorsedda Railway, in fact, one half of what would have become a corbelled archway to protect the formation from an encroaching tip of waste rock.    

Gorsedda is an outstanding example of a mid-nineteenth century slate quarry landform, and tells a story of over-ambitious investment and financial disaster.  


Statement of Significance:

Gorsedda Slate Quarry is a relict landform with a short-lived working history, which is it what has enabled it to survive as a text-book of slate-working methods from the early boom years of the 1850s. The benched galleries and the inclined plane connecting with the working levels and the tips of waste rock on either side of the rock-face represent the technology pioneered at Penrhyn Quarry (NPRN 40564) sixty years earlier. The functional linkages between face and the tips and the different structures and buildings on the site – slate-makers’ shelters, a barracks, an inclined plane – are particularly clear, in a remote upland landscape where earlier rural ways of life went on largely uninterrupted by this commercial failure.  

This site is part of the Slate Landscape of Northwest Wales World Heritage Site, Component Part 4: Gorseddau and Prince of Wales Slate Quarries, Railways and Mill. Inscribed July 2020. 



  • Louise Barker & Dr David Gwyn, March 2018. Slate Landscapes of North-West Wales World Heritage Bid Statements of Significance. (Unpublished Report: Project 401b for Gwynedd Archaeological Trust)  
  • Tirwedd Llechi Gogledd Orllewin Cymru / The Slate Landscape of Northwest Wales. Nomination as a World heritage Site (Nomination Document, January 2020)  
  • Wales Slate World Heritage Site   


Hannah Genders Boyd, RCAHMW, January 2022