Ancient Monuments

History on the Ground

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Dinorwic Quarry

A Scheduled Monument in Llanddeiniolen, Gwynedd

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Latitude: 53.1231 / 53°7'23"N

Longitude: -4.096 / 4°5'45"W

OS Eastings: 259840

OS Northings: 360486

OS Grid: SH598604

Mapcode National: GBR 5R.77HR

Mapcode Global: WH54N.1RTN

Entry Name: Dinorwic Quarry

Scheduled Date: 7 January 2004

Source: Cadw

Source ID: 4007

Cadw Legacy ID: CN337

Schedule Class: Industrial

Category: Slate mill

Period: Post Medieval/Modern

County: Gwynedd

Community: Llanddeiniolen

Traditional County: Caernarfonshire


The monument comprises the remains of the Braich levels of the Dinorwic Slate Quarry, situated to the SE of the huge Garrett pit. Dinorwic Slate Quarry was one of the two largest slate quarries in the world, operating from at least the 1770s until 1969. Slate was quarried from a system of stepped quarries on the open hillside and on the sides of pits, with inclines linking the terraces and workshops. Rail transport links were introduced in 1825 and 1843 and steam locomotives and steam-powered mills were introduced in 1848, enabling the dramatic growth of operations. A programme of further investment from the late 1860s onwards successfully united the different workings, improved internal rail transport and saw the construction of the massive quadrangular workshops at Gilfach Ddu. The upper levels, too remote to be scrapped upon closure of the quarry in 1969, survive largely intact, complete with machinery and rail systems - and offer a textbook illustration of quarry methods of the twentieth century. Features that survive on these upper levels include four substantial counterbalanced inclines, complete with rails, sleepers and drumhouses; structures include gwaliau, a weighbridge house, locomotive sheds and water tanks, an office and caban. Further features of note include a blondin with winding houses; a substantial electrical compressor house; and a large slate mill (the Australia mill), complete with two integral engine houses, saws, catslide extension and smithing hearth, built on a terrace constructed with a huge retaining wall.

The monument is of national importance as an exceptionally well preserved area within one of the most historically significant slate quarries in Wales, containing important evidence of slate quarrying, preparation, transport and infrastructure.

The scheduled area comprises the remains described and an area around them within which related evidence may be expected to survive. It is irregular and measures 600m from NW to SE by up to 220m transversely, as shown in red on the accompanying map extract. The scheduled area in relation to Item A, containing in the main the buildings and features of the built-up level upper terrace, measures 250m from NW to SE by 45m transversely and includes the high drystone retaining wall. The scheduled area in relation to Item B, containing in the main the buildings and features of the lower terrace, measures 310m from NW to SE by up to 210m transversely. The scheduled area in relation to Item C, containing the longest incline to be designated within this current proposal, measures 235m from NE to SW 15m transversely.

Source: Cadw

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