Cilgwyn Quarry

Overview

An open-cast slate quarry on the north side of the Nantlle Valley, Gwynedd, reputed to be the oldest slate quarry in Wales and among the oldest in Europe, with working dating back to the twelfth century. Known from the eighteenth century for its distinctive bright red and purple slates, Cilgwyn's efficient nineteenth-century working methods drew visiting mining engineers from France and Germany. It closed in 1956, and its site is now part of the Slate Landscape of Northwest Wales UNESCO World Heritage Site.

History

Quarrying at Cilgwyn is recorded as far back as the twelfth century, making it — by reputation — the oldest slate quarry in Wales and one of the oldest in Europe. Slates excavated at the Roman fort of Segontium (Caernarfon) are said to have originated in the valley, and King Edward I is reputed to have stayed in a house roofed with Cilgwyn slate during his conquest of Wales. By the eighteenth century the quarry was well known for its distinctively bright red and purple slates, worked from a deposit known as the Faengoch ('Red Vein'). Commercial development intensified from 1800, when the Cilgwyn Quarry Company was formed by the Caernarfon solicitor John Evans; a dam and watercourse he built for the quarry in 1816 became the subject of a legal dispute that went on to influence UK land enclosure law. The quarry passed in the 1820s to the Cilgwyn and Cefn Du Slate Company, which collapsed in 1831; the following management, under banker and MP George Alfred Muskett, itself failed in 1842 with around £10,000 of debt, and a second attempt failed again by 1844 with around £20,000 owed. The quarry was reorganised and resumed operation from the 1850s, eventually worked as four main opencast pits — Gloddfa Glitiau, Old Cilgwyn, Cloddfa'r Coed and Veingoch — served by an extensive network of 2-foot-gauge internal tramways, and shipped slate out via both the Nantlle Railway and, later, the North Wales Narrow Gauge Railways, a dual rail connection unusual among the valley's quarries. An 1825 water-powered rail incline built to clear fallen rock from one of the pits is recorded as one of the earliest uses of that technology in the industry. Cilgwyn's efficient, low-cost open-cast working methods attracted international attention: mining engineers including Hanns Bruno Geinitz and Rudolph Nasse visited repeatedly between the 1850s and 1880s to study them for potential use in France and Germany. Employment peaked between 1864 and 1895, when the quarry employed between 200 and 304 workers, falling to between 51 and 102 by the period 1918-37 as the wider Welsh slate industry declined; 7,430 tons of finished slate were produced in 1882. The Cilgwyn Quarry Company finally ceased trading in 1956. The site was later used as a council waste tip, with landfill activity ending in January 2009, and now forms part of the Nantlle Valley component of the Slate Landscape of Northwest Wales UNESCO World Heritage Site, inscribed in July 2021.

Geology

Slate was worked from the Faengoch ('Red Vein'), which gave Cilgwyn its distinctive red and purple-coloured slates, in contrast to the grey/blue-grey slate typical of most other Welsh quarries.

Workings

Worked as opencast pits rather than underground chambers — chiefly Gloddfa Glitiau, Old Cilgwyn and Veingoch — linked by an internal 2-foot-gauge tramway network, with an 1825 water-powered rail incline used to clear fallen rock, an early example of the technology in the industry.

Closure

The Cilgwyn Quarry Company ceased trading in 1956, ending commercial slate working at the site.

What remains

The former quarry was used as a council rubbish tip for several decades, with landfill activity there ending in January 2009. The site now lies within the Nantlle Valley component of the Slate Landscape of Northwest Wales UNESCO World Heritage Site.

Abandoned workings can be dangerous — unstable ground, uncapped shafts, flooding and bad air are common even where a site looks safe from the surface. This entry describes history and general location only; it is not an access guide.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• Quarrying at Cilgwyn dates to at least the twelfth century, making it reputedly the oldest slate quarry in Wales and one of the oldest in Europe. ¹
• The Cilgwyn Quarry Company was formed in 1800 by John Evans; his 1816 dam and watercourse works became the subject of a dispute that influenced UK land enclosure law. The Cilgwyn and Cefn Du Slate Company took over in the 1820s but collapsed in 1831, and two further managements failed by 1842 and 1844 before the quarry resumed operation in the 1850s. ¹
• 7,430 tons of finished slate were produced in 1882. Employment peaked at 200-304 workers between 1864 and 1895, falling to 51-102 by 1918-37 as the industry declined; the company ceased trading in 1956. ¹
• Worked as opencast pits (Gloddfa Glitiau, Old Cilgwyn, Veingoch) on the Faengoch ('Red Vein') deposit, with an internal 2-foot-gauge tramway network and, from 1825, one of the industry's earliest water-powered rail inclines for clearing fallen rock. ²
• Cilgwyn's efficient open-cast working methods drew visiting mining engineers, including Hanns Bruno Geinitz and Rudolph Nasse, repeatedly between the 1850s and 1880s, who studied them for possible adoption in France and Germany. ³
• The site now lies within the Nantlle Valley Slate Quarry Landscape, a component part of the Slate Landscape of Northwest Wales UNESCO World Heritage Site, inscribed in July 2021. ⁴
• After the quarry closed in 1956 the site was used as a council waste tip, with landfill activity there ending in January 2009. ¹

Sources

1. (secondary) Cilgwyn quarry — Wikipedia
2. (secondary) Slate industry in the Nantlle Valley — Wikipedia
3. (secondary) Nantlle Valley (Journey to the Past heritage trail) — Bangor University
4. (secondary) Slate Landscape of Northwest Wales — Wikipedia

Record created: 26 August 2026 · Last researched: 26 August 2026