Cefn Du Quarry

Overview

A slate quarry on Cefn Du above Llanberis, formed in 1802 from a cluster of small diggings, which took in Chwarel Fawr, Ffridd-glyn, Brynmawr and Bwlch-y-Groes and closed in 1928.

History

Cefn Du quarry lies on the east-facing slope of Cefn Du, west of Llanberis and above Llyn Padarn, the largest of a string of small quarries strung along that hillside. It began in 1802, when a number of little early diggings, among them Cerrig y Pigia, Chwarel Huw Dafydd, Chwarel Morgan, Chwarel Owen and Chwarel y Maen, were brought together under the Cilgwyn and Cefn-du Company. It grew into several pits with a locomotive tramway system and a line to the Ffridd incline down to Llanberis; by 1879 it was said to have four steam engines, two water wheels and a water turbine, and at its height it employed some 200 men.

Cefn Du swallowed its neighbours. Ffridd-glyn (the Cambrian quarry), where an American Burleigh steam drill was tried in 1872-3, joined it in 1878. Chwarel Fawr on the northern slope of Moel Eilio was amalgamated in 1883, after which its rock went through a tunnel to the Cefn Du mill instead of by tramway, and Brynmawr and Bwlch-y-Groes were taken over in 1886. Being one of the small quarries, it had no hospital like the great Dinorwic quarry nearby, and a man badly hurt by a rockfall in December 1880 was carried home on a bier by his workmates; John Pritchard of Llanrug was killed by a falling rock in July 1904. In June 1917 the quarry was stopped, after working with few breaks for some eighty years, leaving its mostly older workmen unable to go far for work. Cefn Du closed in 1928.

Geology

Unknown.

Workings

Several pits linked by tunnels and a locomotive tramway, with a tunnel from Chwarel Fawr after 1883 and a tramway to the head of the Ffridd incline.

Closure

Stopped in 1917 and closed in 1928.

What remains

The pits and tunnels are much collapsed; ruined buildings stand in the mills area, and the tramway formation to the Ffridd incline is still visible near two barracks.

The main pit, collapsed tunnels, the ruins of a large mill partly built of an unusual green rock, stacking sheds, two barracks and the tramway formation.

Redevelopment

Open hillside.

Related mines

• Cook and Ddol Quarry — Neighbouring quarries on the slope above Llanberis, both sending slate down the Ffridd incline.

Recorded claims

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

• Cefn Du quarry originated in 1802 when several small early diggings were amalgamated into the Cilgwyn and Cefn-du Company. ^1,2
• By 1879 Cefn Du was said to have four steam engines, two water wheels and a water turbine. ¹
• Chwarel Fawr was amalgamated with Cefn Du in 1883, after which its material went by tunnel to Cefn Du for processing. ³
• Brynmawr and Bwlch-y-Groes quarries were taken over by Cefn Du in 1886, and Ffridd-glyn in 1878. ^4,5,6
• John Pritchard of Llanrug, aged 36, was killed by a falling rock at Cefndu Quarry in July 1904. ⁷
• Cefn Du quarry was stopped in June 1917 after some eighty years of almost continuous working. ⁸
• Cefn Du quarry closed in 1928. ^1,2

Sources

1. (secondary) Chwarel Cefn-Du Slate Quarry (NPRN 400667) — Coflein (RCAHMW)
2. (observational) The Main Pit of Cefn Du Quarry (Geograph 229776) — Geograph Britain and Ireland
3. (secondary) Chwarel Fawr Slate Quarry (NPRN 400668) — Coflein (RCAHMW)
4. (secondary) Bryn-Mawr Slate Quarry I (NPRN 400669) — Coflein (RCAHMW)
5. (secondary) Chwarel Bwlch-y-Groes Slate Quarry (NPRN 400672) — Coflein (RCAHMW)
6. (secondary) Ffridd-Glyn Slate Quarry; Cambrian Slate Quarry (NPRN 400670) — Coflein (RCAHMW)
7. (primary) The North Wales Express, 22 July 1904: Fatal quarry accident — The North Wales Express (Welsh Newspapers Online, National Library of Wales)
8. (primary) Y Genedl, 12 June 1917: Waenfawr: atal chwarel — Y Genedl (Welsh Newspapers Online, National Library of Wales)

Record created: 20 October 2026 · Last researched: 20 October 2026