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Site Details

NPRN 570

Map Reference SH66NW

Grid Reference SH6150466360

Unitary (Local) Authority Gwynedd

Old County Caernarfonshire

Community Llandygai



Period 20th Century, 19th Century

Site Description The industrial complex known as y felin fawr (‘the big mill’) is situated to the north of Penrhyn Slate Quarry, at the first location where the Penrhyn Quarry Railroad crossed a stream strong enough to turn water-wheels. This was where slate slabs from Penrhyn quarry were sawn and shaped,and where the quarry’s engineering needs were met. It operated until 1965 and is now managed by a community enterprise as light industrial units, and for retail purposes.

It is significant as the first location in the world where stone is known to have been processed by circular saws, by 1802, shortly predating the use of circular saws to saw lignum vitae at the Royal Navy’s Portsmouth Block Mills in the following year. It also demonstrates the evolution of slate
processing within the slate industry of north-west Wales. No trace is evident of the first mill, nor of its successors erected c. 1846 and in 1855, since the two present mills date from 1865-6, and are to the design of William Francis, the quarry manager.

Engineering facilities include a foundry dating from 1866 which replaced an earlier structure erected in 1834, the blast provided by a suspension water-wheel which survives in a building to the eastern perimeter of the site, by Henry Sugden and Son of Bramley, near Leeds. The houses Tai'r Stablau were built in 1875 on the site of stables for the horses that formerly pulled the slate wagons to Port Penrhyn; the slate slab-built shed added against the southern gable wall of the western mill was built in the same year for the first steam locomotive on the Penrhyn Quarry Railway, with a later siding for an internal combustion locomotive. Later structures include a two-bay locomotive repair shop, built out of sawn slate blocks; the more northerly range housed a range of machine tools, in the other an inspection pit and an overhead gantry crane survive.

The river which powered the complex follows its original course and is apparent both upstream and downstream. The culvert through which it crosses under the site is accessible. Two waterwheels survive on site, one of which is situated between the two slate-slab mills, which it formerly powered, the other on the eastern perimeter, which formerly provided the blast for the foundry.

Other buildings and structures on the site include slate-makers’ shelters (gwaliau) where broken slates were trimmed for commercial sale. At the southern perimeter of the site, where the railway passed into the quarry, is a fine slate-slab road over-bridge dating from 1900.

Louise Barker, RCAHMW, April 2018]

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).

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