The slate mill was built in the late 1870s, of slate waste with a slate roof supported on king-post timber trusses; the roof slates were removed c1997. It was built to house twenty-seven hydraulic-feed slate saws made by De Wintons of Carnarfon, and twenty-six dressing machines. It was originally powered by a remote waterwheel, the power being transmitted by wire rope, but in 1906 electric motors were substituted. The line-shafting for the saw tables is still in situ.

Information from Cadw Listed Buildings database.

W J Crompton, RCAHMW, 16 January 2014.

2.

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.    

Sources:   

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 (Unpublished Report: Project 401b for Gwynedd Archaeological Trust)   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 https://www.llechi.cymru/    

H. Genders Boyd, RCAHMW, January 2022