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Pen-yr-Orsedd Slate Quarry, Nantlle Valley

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Map ReferenceSH55SW
Grid ReferenceSH5086053790
Unitary (Local) AuthorityGwynedd
Old CountyCaernarfonshire
Period19th Century

The Pen-yr-orsedd Slate Quarry is located to the north of Nantlle village. An open working, it opened in about 1816 as hillside galleries. Mills were built on three successive levels, the first in 1860 and the next, their first integrated mill, in 1870. The upper mill followed in 1898. Output in 1882 was 8251 tons with 230 men employed. Output was far higher in the 1890s with 613 men employed in 1898. The first connection to the Nantlle railway was by incline via Pen y Bryn (NPRN 33674) until this area was tipped on and direct connection to the railway was made. After closure of the Nantlle line in 1963 road transport was used. The quarry was made up of a series of pits and its most notable feature in the later years was the complex series of four aerial ropeways known as 'Blondins', with Bruce Peebles electrical equipment of 1906. The use of the Blondins gradually ceased, a lorry road being built down into one pit in use in the 1980s. There is also a surviving engine house on the site. The quarry remained in use, as small scale workings from the 1980s until production ceased in about 2000.
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.54-5.

RCAHMW, 3 November 2011.


Statement of Significance 

The relict Pen yr Orsedd Slate Quarry grew to be one of the two largest slate quarries in the Nantlle valley. As a series of hillside pits draining into an undergound channel, it did not face the challenge of pumping to the same extent as other nearby quarries, and was able to adopt a mechanised and engineered approach to the quarrying of slate, evident in the use of water, steam, electricity and compressed air on site, as well as in its well-ordered mill buildings arranged to take advantage of the limited water-power available in the valley. It retains its electrically powered blondin ropeways and motor houses on the upper level (NPRN 33734) and its workshops.  

This site is part of the Slate Landscape of Northwest Wales World Heritage Site, Component Part 3: Nantlle Valley Slate Quarry Landscape. 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    


H. Genders Boyd, RCAHMW, January 2022

application/pdfRCAHMW ExhibitionsBilingual exhibition panel entitled Y Diwydiant Llechi. The Slate Industry, produced by RCAHMW for the Royal Welsh Show, 2011.
application/pdfGAT - Gwynedd Archaeological Trust ReportsLevel 2 photographic building record report entitled, "Building 54 and 54a: Pen Yr Orsedd Slate Quarry, Nantlle". The report was prepared for Welsh Slate by Gwynedd Archaeological Trust, GAT Project No. 2071. Report number 835.
application/pdfRCAHMW ExhibitionsExhibition panel entitled Y Diwydiant Llechi, produced by RCAHMW for the National Eisteddfod 2005.