Clynmill Colliery

Overview

A coal and ironstone working of the Plymouth Ironworks at Merthyr Tydfil, a water-balance pit by 1850, later worked by drift by Hill's Plymouth Company with over 300 men until its reserves were given to Graig Colliery in 1921.

History

Clynmill, or Clyn-Mil, lay at Merthyr Tydfil on land of the St Fagans estate, later the Plymouth Iron Company's, where the ironworks had been getting coal and ironstone since the end of the eighteenth century; the farm of Lower Clyn-Mil served as the works stables. The Clyn-Mil No. 1 pit, working coal and ironstone, was a water-balance pit with its own reservoir, and a level drained its water to the Pen Cae Bach pit. It was working before 1850, when a man was killed there, and a ten-year-old boy died under a fall of roof in November 1853. Working grew in the period 1850 to 1875, when the No. 1 and New Pits near Cwmblacks were in work and a great tip was built up, reached by tramroad from No. 1. In 1862 the No. 1 pit was reckoned to hold 816,000 tons of ironstone and Nos. 2 and 3 another 524,000.

The Plymouth Iron Company held it in 1871 and the Aberdare Plymouth Company from 1877. By 1882 No. 1 was working ironstone only and No. 2, 130 yards deep, the Lower Four Feet at 150 tons a day. Messrs. Hankey brought in haulage machines and sank the Jacky pit to the Lower Four Feet, but after the Plymouth Works' mortgagees took over in 1884 it was abandoned in 1887, the seam thinning and the workings far from the shafts. Hill's Plymouth Company reopened it in 1898, working the Lower Four Feet and Five-and-a-half seams; it closed in 1902, restarted from the drift in 1903, met a large fault in 1907 that took a year to cross, and in 1911-12 tried mechanical coal cutters. It employed 317 men in 1907 and 334 in 1913, raising steam coal, and 227 in 1918. In 1921 the company stopped it and gave its remaining reserves to Graig Colliery. The tip survives in a semi-landscaped state.

Geology

South Wales coalfield, Merthyr: ironstone with the Lower Four Feet, Five-and-a-half, Nine Feet, Upper Four Feet, Upper Six Feet and Lower Yard seams, in ground broken by faulting.

Workings

The No. 1 pit (water balance, coal and ironstone), Nos. 2 and 3, the New Pits near Cwmblacks, the Jacky pit and a drift; a draining level to Pen Cae Bach pit.

Closure

Abandoned in 1887 and reopened in 1898; worked by Hill's Plymouth until 1921, when its reserves were allocated to Graig Colliery.

What remains

A large tip, in a semi-landscaped state.

Redevelopment

Unknown.

Related mines

• Graig Colliery, Pentrebach — Both Hill's Plymouth pits; in 1921 Clynmill's remaining reserves were allocated to Graig Colliery.

Recorded claims

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

• The Clyn-Mil No. 1 pit, for coal and ironstone, was a water-balance pit with its own reservoir. ^1,2
• Clynmill belonged to the Plymouth Iron Company's workings; the Plymouth Iron Company owned it in 1871. ^1,2
• In 1862 the No. 1 pit was estimated to hold 816,000 tons of ironstone. ¹
• The colliery was abandoned in 1887 when the seam thinned. ¹
• Hill's Plymouth Company employed 334 men there in 1913, raising steam coal. ¹
• In 1921 Hill's Plymouth stopped Clynmill and allocated its reserves to Graig Colliery. ¹
• A large tip connected by tramroad to Clyn-Mil No. 1 survives, semi-landscaped. ²
• By 1901-1905 both Clyn-Mil pits were shown as disused. ²
• BGS holds a group plan of South Duffryn, Pencaebach, Abercanaid and No. 2 Clynmill. ³

Photographs & further reading

Sources

1. (secondary) Clynmill Colliery (Northern Mine Research Society) — Northern Mine Research Society
2. (secondary) Clyn-Mil, Pencoedcae and Trebeddau (Historic Landscape Character Area, Merthyr Tydfil) — Heneb
3. (primary) BGS mine plan: South Duffryn / Pencaebach / Abercanaid / No 2 Clynmill ..., Upper Four Feet — British Geological Survey

Record created: 6 October 2026 · Last researched: 6 October 2026