Mountain Pit, Tredegar

Overview

The Tredegar Iron Company's No. 7 pit, sunk in 1841 to 630 feet, claimed as the deepest water-balance pit in South Wales and perhaps the world, which raised over 50,000 tons a year in its last decade and stopped in 1896.

History

Mountain Pit, the No. 7 pit of the Tredegar Iron Company in the Sirhowy valley, was sunk in 1841 with a shaft ten feet across to a depth of 630 feet, and was claimed to be the deepest water-balance pit in South Wales and probably the world. In water-balance winding a tank under the carriage at the top was filled with water until its weight drew up the loaded carriage from the bottom, and the water was then let out below; the method was common in the shallow pits along the northern rim of the coalfield until steam winding overtook it in the 1870s.

In 1888 Mountain Pit was working the Engine Coal at 45 inches, the Yard seam at 26 inches and the Old Coal at 37 inches. It raised 52,800 tons in 1889 and 39,538 tons in 1894. It was stopped in 1896, or closed in 1897 by another account, and in 1900 only seven men worked at the surface.

Geology

South Wales Coalfield: the Engine Coal, Yard and Old Coal seams.

Workings

A ten-foot shaft 630 feet deep, wound by water balance.

Closure

Stopped in 1896 (or 1897); seven surface men remained in 1900.

What remains

Unknown.

Redevelopment

Unknown.

Related mines

• Ash Tree Pit, Tredegar — Tredegar Iron Company water-balance pits above the ironworks.
• Dukes Pit, Tredegar — Tredegar Iron Company workings around the Tredegar ironworks.
• Yard Level, Tredegar — Tredegar Iron Company coal workings above the ironworks.

What's uncertain

Points where sources disagree or the record could not be settled; both accounts are kept. All open questions in the archive.

• It was stopped in 1896. (disputed) ¹
• It probably closed in 1897; seven men worked at the surface in 1900. (disputed) ²

Recorded claims

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

• Mountain Pit, Tredegar No. 7, was sunk in 1841 to 630 feet with a ten-foot shaft. ^1,2
• It was claimed to be the deepest water-balance pit in the world. ^1,3,2
• In 1888 it worked the Engine Coal (45 in), Yard (26 in) and Old Coal (37 in). ²
• It produced 52,800 tons in 1889 and 39,538 tons in 1894. ¹
• It was stopped in 1896. (disputed) ¹
• It probably closed in 1897; seven men worked at the surface in 1900. (disputed) ²

Sources

1. (secondary) NMRS: The Tredegar collieries — Northern Mine Research Society
2. (secondary) Engine Pit, Mountain Colliery and Ash Tree Colliery, Tredegar — Welsh Coal Mines
3. (secondary) NMRS: The Brynpwllog headgear now at Big Pit (water balance winding) — Northern Mine Research Society

Record created: 18 October 2026 · Last researched: 18 October 2026