Mostyn Colliery

Overview

A colliery on the Dee estuary worked, by some accounts, from the thirteenth century until 1884 — possibly the longest continuously worked coal mine in Wales. By the seventeenth century it may have been the largest colliery on Britain's western seaboard. It is also the source of one of the earliest first-hand descriptions of a firedamp explosion anywhere, written by Sir Roger Mostyn in 1675. In July 1884 the estuary broke into the workings and no amount of pumping could answer it: the sea was coming in, and six centuries of mining ended in a week.

History

Thomas Pennant wrote that coal mines at Mostyn were established as far back as 1261. Records show the colliery, with a stone quarry, worth £5 a year in 1294 and £3 6s 8d in 1423. Coal went out by boats coming to the quay at high water, and as the river shifted its course a partial canal was cut to keep the passage safe. Thomas Cowper and Richard Mason of London leased the colliery in 1594 and sold a thirteen-year lease to Roger Mostyn in 1602 for £70, beginning the association with the family that would run it. Mostyn expanded: three pits by 1616, and by 1619 the colliery was worth some £700 a year. Sir Roger Mostyn ordered three more deep pits sunk in 1639, and around this time almost all coal shipped from Chester was entered in the city records as 'Mostyn coal'. By the seventeenth century Mostyn was possibly the largest colliery on the western seaboard of Britain and probably the most profitable in the North Wales coalfield. An ironworks opened in 1802 to use the colliery's coal and the concern was renamed the Mostyn Coal and Iron Company. The nineteenth century brought both prosperity and repeated catastrophe underground. Robert Anderson's 1839 pamphlet on the coal trade priced Mostyn's best coals at 8s 6d a ton and its seconds a shilling less, among the cheapest in Britain. By the 1840s the quay could take vessels of 300 tons moving 50,000 to 60,000 tons of coal a year. Work began in 1843 on the Bychan Embankment — the 'cob' — 1,974 yards long, funded by Lord Mostyn and J. P. Eyton at about £4,500, which reclaimed some 70 acres from the Dee and served as flood defence. In November 1848 the Haigh Foundry cast what was believed to be one of the largest steam engine cylinders in the world for a direct-action pumping engine here: 17 feet long, 8 ft 4 in in diameter, 22 tons, and 30 tons of molten metal in the making. In 1852 Mostyn became one of the first collieries to fit an experimental air pump. Sidings to the Chester and Holyhead Railway were built in 1855, though the colliery had had its own horse-drawn system since the early eighteenth century. The Mostyn Coal and Iron Company went into liquidation in 1879 and the lease was sold on. In July 1884 the river broke through and overwhelmed the pits (see Disasters, below). The colliery never reopened, despite a takeover in 1887 forming the Darwen and Mostyn Iron Company. Serious exploration was by then under way at nearby Point of Ayr, which became one of the last deep coal mines in Wales when it closed in 1996.

Geology

The colliery worked the coal measures of the North Wales coalfield where they run out beneath the Dee estuary — the same seams that were later pursued at Point of Ayr. Working under an estuary was the whole risk of the place: the pits were taken out beneath water-bearing ground, and it was the sea, not the strata, that finished them. The mine was worked on the pillar and stall method, coal being left in pillars to hold the roof, so the condition of those pillars was a standing subject of argument between profit and safety.

Geological setting: Sedimentary Beds and Seams (well documented example)

Workings

Pits sunk successively from the seventeenth century — three by 1616 and three more deep pits from 1639 — worked pillar and stall, with coal shipped from a quay on the estuary that by the 1840s took vessels of 300 tons. An internal horse-drawn railway ran from the early eighteenth century, and sidings connected to the Chester and Holyhead Railway in 1855. Pumping was on a heroic scale: the 1848 Haigh Foundry cylinder for the direct-action pumping engine was thought to be among the largest in the world. An experimental air pump was fitted in 1852, among the first at any colliery.

Closure

In July 1884 water from the estuary broke into the workings in huge quantities. Pumping made no difference at all, because the water was coming in from the sea. Around two hundred men and boys lost their employment, and the colliery never reopened, though the ironworks carried on with coal imported from Lancashire. Sources differ on the length of working the flood ended: Wikipedia gives over 620 years, another account 823 years, the difference resting on which of the thirteenth-century starting dates is taken.

What remains

Nothing of the colliery survives as a working site. The Bychan Embankment of 1843 and the reclaimed ground behind it remain part of the estuary shore, and the area around the former colliery and ironworks is now industrial, Warwick Chemicals occupying ground shown on the 1881 Ordnance Survey as a copper works and Ayton Pit.

No colliery structures identified in the sources read; the 1843 Bychan Embankment and the land it reclaimed survive on the estuary shore.

Disasters & major incidents

• Mostyn Colliery Inundation, 1884
  July 1884 · Flooding / Inundation · 0 fatalities
  In July 1884 water from the Dee estuary broke into Mostyn Colliery in huge quantities. Pumping made no difference, because the water was coming in from the sea. Around two hundred men and boys lost their work, the colliery never reopened, and coal mining at Mostyn ended after some six centuries.

Recorded claims

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

• Thomas Pennant wrote that coal mines at Mostyn were established as far back as 1261; records show the colliery, together with a stone quarry, worth £5 a year in 1294 and £3 6s 8d in 1423. ¹
• Cowper and Mason sold a thirteen-year lease to Roger Mostyn in 1602 for £70; there were three pits by 1616, the colliery was worth about £700 a year by 1619, and Sir Roger Mostyn ordered three more deep pits sunk in 1639. ^1,2
• By the seventeenth century Mostyn was possibly the largest colliery on the western seaboard of Britain and probably the most profitable on the North Wales coalfield; around 1639 almost all coal shipped from Chester was entered in the city records as 'Mostyn coal'. ¹
• Sir Roger Mostyn gave an account of a firedamp explosion on 3 February 1675 in which the blast 'flew to and fro over all the hollows of the work with a great wind and a continued fire', was heard fifteen miles away, destroyed the winding gear and felled trees, and left men underground singed as if whipped with rods, some carried fifteen or sixteen yards and beaten against the roof of the coal. ¹
• Robert Anderson's 1839 pamphlet gave Mostyn's 'best coals' at 8s 6d a ton and 'second coals' a shilling less, among the cheapest available in Britain. ¹
• Work began in 1843 on the Bychan Embankment, 1,974 yards long, funded by Lord Mostyn and J. P. Eyton at about £4,500, which reclaimed some 70 acres from the River Dee and served as flood defence. ¹
• In November 1848 the Haigh Foundry cast for Mostyn what was believed to be one of the largest steam engine cylinders in the world — 17 feet long, 8 ft 4 in in diameter and 22 tons — for a direct-action pumping engine, using 30 tons of molten metal. ¹
• The mine was worked on the pillar and stall method, coal being left in pillars to support the roof, so that the balance between profit and safety turned on how much was left and on the condition of the pillars. ³
• Accounts differ on how long coal had been worked when the 1884 flood ended it: over 620 years by one reckoning and 823 years by another, the difference resting on which thirteenth-century start date is taken. (disputed) ^1,3

Photographs & further reading

Sources

1. (secondary) Mostyn Colliery — Wikipedia
2. (secondary) The development of the Mostyn Colliery (17th century) — Mostyn Estates
3. (secondary) The miners of Mostyn — Heritage Hunter

Record created: 3 September 2026 · Last researched: 3 September 2026