Mynachdy Colliery

Overview

A small, unprofitable and turbulent Ynysybwl colliery: workings on the site from the 1870s, reopened slightly to the north in 1903 for house coal from the Darren Ddu seam and closed for good in 1943, with its powder shed and stable ruins still in the undergrowth.

History

Mynachdy Colliery lies on the east side of the Clydach valley at Ynysybwl, north of Pontypridd. There were workings here well before the colliery of the record: earlier pits a little to the south were worked intermittently from the 1870s to the 1890s, and they mattered enough to shape the valley's railway. When the Taff Vale Railway came to plan its Ynysybwl branch the mining it was meant to serve had barely begun, and only the Mynachdy and Black Grove collieries were providing any business at all; the company had to seek an extension of time in 1877, let the contract to J. E. Billups only in October 1880, and probably opened the line in 1885. The branch was steeply graded towards its head, reaching one in thirty, and for many years trains were propelled beyond Mynachdy rather than hauled. The colliery proper opened in 1903, a short distance north of the abandoned older workings, and was worked for house coal from the Darren Ddu seam by the Mynachdy Colliery Company. It never prospered. The Royal Commission's record of it is blunt about why its history was so turbulent: the lack of profitability, and the small numbers of men who worked there. It was finally closed in 1943 and never worked again. Something of it is still there. Hidden now in the undergrowth, the powder shed survives with the stonework worn where barrels of powder once rested on it, and the ruins of the stable block can still be made out.

Geology

Worked house coal from the Cefn Glas and Darren Ddu seams of the South Wales coalfield; the Darren Ddu here was thin, some eighteen inches of coal between bands of dirt.

Workings

Worked house coal from the Darren Ddu seam from 1903, on ground a little north of the older workings abandoned in the 1890s. It was a small working throughout, and a powder shed and a stable block stood among its surface buildings.

Closure

Never profitable, the colliery abandoned the Darren Ddu seam and closed in 1943, and was never worked again.

What remains

Overgrown. The colliery buildings have gone to ruin and the site is under undergrowth, with the powder shed and the stable block the clearest survivals.

The powder shed, its stonework worn where powder barrels were rested, and the ruins of the former stable block.

Redevelopment

Unknown.

Nearby mines

• Lady Windsor Colliery — 0.7 km W
• Abercynon Colliery — 1.2 km E
• Penrikyber Colliery — 1.5 km NW
• Albion Colliery — 2.2 km SE
• Deep Navigation Colliery — 2.6 km E, Merthyr Tydfil

Straight-line distance, within 15 km. Show on the map.

Recorded claims

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

• Mynachdy Colliery opened in 1903, a little north of earlier workings that had been worked intermittently from the 1870s to the 1890s. ¹
• It was reopened in 1903 by the Mynachdy Colliery Company Limited of Cardiff, with Frederick W. Holman as chairman and managing director. ²
• Worked house coal from the Cefn Glas and Darren Ddu seams by the longwall method. ²
• It employed about 295 men in 1913 and 1916, falling to 190 by 1918 and to a handful by its last years. ²
• The colliery abandoned the Darren Ddu seam and closed in 1943, and was never worked again. ^2,1
• The colliery of 1903 opened slightly to the north of earlier workings which had been worked intermittently from the 1870s to the 1890s and then abandoned. ¹
• The Royal Commission's record attributes the colliery's turbulent history to its lack of profitability and to the small numbers of men who worked there. It closed in 1943 and was never worked again. ¹
• When the Taff Vale Railway came to build its Ynysybwl branch, mining in the valley was so limited that only the Mynachdy and Black Grove collieries were providing any traffic; the contract was let in October 1880 and the line probably opened in 1885. The branch reached a gradient of one in thirty near its head, and for many years trains were propelled beyond Mynachdy for safety. ³
• The powder shed still stands in the undergrowth, its stonework worn where barrels of powder were once rested, and the ruins of the former stable block are still apparent. ¹

Photographs & further reading

Sources

1. (primary) Mynachdy Colliery, Ynysybwl — Coflein (Royal Commission on the Ancient and Historical Monuments of Wales)
2. (secondary) Lady Windsor, Ynysybwl — Welsh Coal Mines
3. (secondary) Ynysybwl branch line railway — Wikipedia
4. (primary) Darranddu / Mynachdy abandonment plans (BGS mine-plans catalogue) — British Geological Survey

Record created: 23 September 2026 · Last researched: 23 September 2026