Bath stone

How does it form?

In the Middle Jurassic, the Bath area lay beneath a warm, shallow sea. On the seabed, tiny shell fragments and sand grains rolled by waves and currents grew into round grains called ooids as layer after layer of lime settled on them. These grains piled up in thick beds together with fragments of shells and crinoids; then the spaces between them filled with crystalline calcite cement and the sediment hardened into rock.

Bath stone belongs to the Chalfield Oolite Formation in the rock sequence geologists call the Great Oolite Group, especially its Combe Down Oolite and Bath Oolite members. Because there is little mud between the grains and no strong grain direction, the stone can be sawn in any direction; masons call such stones freestones. Freshly quarried stone contains moisture known as “quarry sap”, which makes it soft and easy to work; it hardens as it dries.

What is it used for?

• Roman and medieval times: It was used in Roman villas at Box and Bathford and in parts of the Roman baths at Bath. In the Middle Ages it went into Lacock Abbey, and later into Longleat House.
• Georgian Bath: In the early 18th century the postmaster Ralph Allen bought the quarries at Combe Down and promoted the stone; the architect John Wood and his son designed buildings such as the Royal Crescent and the Circus in it. Pulteney Bridge and Bath Abbey are of Bath stone too. Today the whole city is a UNESCO World Heritage Site.
• Across the country and the world: The Kennet and Avon Canal (1794–1810) and the Great Western Railway made it easier to ship the stone to London. Buckingham Palace, Lancaster House, Apsley House, the Royal Pavilion in Brighton and, abroad, Cape Town City Hall all use it.
• Today: It is used for walling, ashlar facades, window and door surrounds, fireplaces and sculpture. It is not recommended for floors, because it wears quickly.

Where is it found?

Bath stone is quarried on the border of Somerset and Wiltshire, in the area between Bath, Bradford-on-Avon and Corsham. The main old quarries and mines were around Combe Down, Bathampton Down, Box, Monkton Farleigh and Limpley Stoke. Most of the stone was mined underground in chambers, with pillars left to hold up the roof; at Box, digging began in Roman times and went on until 1968. Demand fell in the economic depression of the 1930s, many quarries were handed over to the military in the Second World War, and the industry never fully recovered. Today the stone is taken mainly from underground quarries around Corsham, such as Hartham Park and Monk’s Park, and Stoke Hill mine is also still worked.