Merstham Chalk Mines

Overview

Underground stone mines worked into the North Downs escarpment at Merstham for perhaps a thousand years, supplying the calcareous 'firestone' building stone used at Westminster, Windsor Castle and Old St Paul's — and, in 1868, the site where Alfred Nobel gave a public demonstration of dynamite.

History

Merstham's underground stone workings are believed, from archaeological and documentary evidence, to have been worked continuously from the 7th or 8th centuries until 1961 — one of the longest working lives of any mine in Britain. The mines were driven into the Upper Greensand, the bed of soft, calcareous sandstone known locally as firestone or Malm stone, which outcrops along the North Downs escarpment through Godstone, Bletchingley, Merstham and beyond; the stone is soft when freshly dug and must be seasoned and laid in the same orientation it lay underground if it is to last. Merstham firestone supplied some of medieval England's grandest building projects — the king's palace at Westminster in 1259, Windsor Castle in 1359, and Old St Paul's Cathedral and London Bridge. Operations were important enough in the Middle Ages that the mines were taken into Crown ownership, and the Prophete family controlled working here through the 14th century.

The Croydon, Merstham and Godstone Iron Railway, an extension of the Surrey Iron Railway — itself the world's first public railway — opened in 1805 to carry stone and lime from Merstham to Croydon by horse traction, closing around 1840 as the London to Brighton railway was being built. As building tastes and transport improved through the 18th and 19th centuries and other building stones became more easily available, the underground stone trade at Merstham declined, reviving only on a smaller scale as a source of hearthstone, used for whitening doorsteps, stone floors and hearths. In July 1868, Alfred Nobel gave a public demonstration of his newly invented dynamite in one of Merstham's chalk quarries, at Price's Grey-lime Stone quarry.

Geology

The Upper Greensand of east Surrey, which between Reigate and Godstone carries beds of building stone known as Reigate stone or firestone - a calcareous sandstone, soft to cut when freshly raised and hardening on exposure, lying in a bed up to forty feet thick at Quarry Dean. Above and within the same formation are the hearthstone layers, a softer variety cut for whitening doorsteps and hearths; the two can be told apart petrologically but not traced back to the particular mine they came from. This is not chalk country in the mining sense: Surrey has very few chalk mines and they are of very limited extent.

Workings

Underground quarries on the pillar-and-stall system, pillars of rock left standing to hold the roof, by which as much as eighty per cent of the stone was taken out at Reigate, Merstham, Chaldon and Godstone. Cast-iron plate rails ran in the Merstham and Godstone workings, though the accepted view since 1986 is that they did not come from the Croydon, Merstham and Godstone Iron Railway that served the surface works. Quarry Dean, at TQ 299 538, is the best documented of the Merstham mines: a section of its stone-brick lining carries Roman characteristics, and it worked until the end of the seventeenth century.

Closure

The underground stone trade declined from the 18th century as transport improved and other building stones became easier to source, surviving latterly as a smaller hearthstone trade before the last workings finally closed in 1961.

What remains

Many of the pillars have collapsed and weathered into the rock around them, so that stretches of the workings look more like natural cave than cut quarry; a 2020 visit to Quarry Dean reached it by rope. Quarry Dean's entrances were filled when it closed at the end of the seventeenth century and it was re-excavated by a farmer at Quarry Dean in the 1960s, since when it has remained open. The wider system of galleries between Reigate and Godstone runs to many miles and has been under detailed study since the 1960s.

The mines are underground and their surface traces are slight. What survives above ground belongs to the trade rather than the working: the line of the Croydon, Merstham and Godstone Iron Railway, opened in 1805 from the Merstham lime works and stone quarries to Croydon, and the lime-burning ground at Merstham itself.

Redevelopment

The abandoned galleries have been put to a series of later uses, among them mushroom-growing and wartime secure storage for precious items.

Related mines

• Godstone Mine — Two of the four main Upper Greensand firestone districts of east Surrey, worked on the same pillar and stall system and studied together; both had plate rails from the Croydon, Merstham and Godstone Iron Railway, and Peter Burgess's study of those rails covers the two side by side.

The underground workings are hazardous and not open to casual access — this entry describes history only, not an access guide.

Recorded claims

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

• Archaeological and documentary evidence indicates the stone mines were worked from the 7th or 8th centuries until 1961. ¹
• Merstham firestone was used at Westminster in 1259, Windsor Castle in 1359, and Old St Paul's Cathedral and London Bridge; the mines were important enough to be taken into Crown ownership in the Middle Ages. ¹
• The Croydon, Merstham and Godstone Iron Railway, an extension of the world's first public railway, opened in 1805 to carry stone and lime to Croydon by horse traction, closing around 1840. ²
• Alfred Nobel gave a public demonstration of dynamite in Merstham's Price's Grey-lime Stone quarry in July 1868. ²
• The stone worked underground at Merstham is Reigate stone, known to the trade as firestone: a calcareous sandstone from the Upper Greensand, found in a bed up to forty feet thick at Quarry Dean. Surrey, unlike Kent and Essex, has very few chalk mines, and those it has are very limited in extent; the Merstham workings are not among them. ^3,4
• The workings were nearly always underground and were developed on the pillar-and-stall system, leaving pillars of rock to hold the roof. By that method up to eighty per cent of the stone was removed from the workings at Reigate, Merstham, Chaldon and Godstone. Many of the pillars have since collapsed and weathered into the surrounding rock, so that parts of the workings read more like natural cave than quarry. ^5,4
• Quarry Dean, at TQ 299 538, carries Roman characteristics in a section of its stone-brick lining, but no record of it appears until 1522, in a reference to the nearby Quarrepitden farmhouse. It worked until the end of the seventeenth century, when it closed and had its entrances filled, and was re-excavated by a Mr Harrison who farmed at Quarry Dean in the 1960s. ^6,4
• Dating the individual workings is genuinely hard: mining technique changed little over the centuries, and the only pottery recovered from the mines older than the Victorian period is a mid-sixteenth-century jug from Bedlams Bank. Archaeological work at New Palace Yard, Westminster, found a fragment of Reigate stone rubble in a context associated exclusively with Roman ceramic building material - rare in Roman levels in London, though common in the medieval period. ⁶
• An attempt in 1994 to provenance Reigate stone samples in the Museum of London by X-ray diffraction, scanning electron microscope and inductively coupled plasma spectroscopy could distinguish firestone strata from hearthstone layers, and could tell which samples shared a source, but could not identify what those sources were. ⁶
• Cast-iron plate rails were used in the Merstham and Godstone quarries. Bean and Osborne concluded there was no evidence they had been acquired from the Croydon, Merstham and Godstone Iron Railway, which used plate rails throughout its nine or so miles; that has been the accepted view among those studying the Surrey firestone workings since 1986. ⁵
• The Croydon, Merstham and Godstone Iron Railway opened in 1805 from the lime works and nearby stone quarries at Merstham to Croydon, where it made an end-on junction with the Surrey Iron Railway running to the Thames at Wandsworth. It was never extended beyond Merstham to Reigate or Godstone as planned, and was effectively out of use once the London and Brighton Railway was completed in 1841. ⁵
• The abandoned galleries between Reigate and Godstone run to many miles and have been put to a variety of later uses, among them mushroom-growing and wartime secure storage for precious items; they have been under detailed study since the 1960s. ³

Photographs & further reading

Sources

1. (primary) Parishes: Merstham — Victoria County History (British History Online)
2. (secondary) History of Merstham — Reigate and Redhill Society
3. (primary) Underground Surrey — Wealden Cave & Mine Society
4. (observational) Quarry Dean Firestone Mine, Merstham, Surrey — June 2020 — 28DaysLater
5. (secondary) Plate Rails in the Surrey Firestone Quarries (Peter Burgess) — Railway & Canal Historical Society
6. (secondary) How Old Are Merstham Mines? (Martin Hatton) — Croydon Caving Club — Croydon Caving Club

Record created: 27 August 2026 · Last researched: 28 September 2026