Bath Stone is an Oolitic Limestone comprising granular fragments of calcium carbonate. Originally obtained from the Combe Down and Bathampton Down Mines under Combe Down, Somerset, England, its warm, honey colouring gives the World Heritage City of Bath, England its distinctive appearance. An important feature of Bath Stone is that it is a freestone, that is one that can be sawn or 'squared up' in any direction, unlike other rocks such as slate which forms distinct layers.

Bath Stone has been used extensively as a building material throughout southern England for churches, houses and public buildings such as railway stations.

Some of the quarries from which the stone was taken are still in use; however the majority have been converted to other purposes or are being filled in.

Geological formation

During the Jurassic Period (195 to 135 million years ago) the region that is now Bath was under a shallow sea. Layers of Marine sediment built and individual spherical grains were coated with lime as they rolled around the sea bed forming the Bathonian Series of rocks. Under the microscope, these grains or ooliths (egg stone) are sedimentary rock formed from ooids, spherical grains composed of concentric layers. The name derives from the Hellenic word òoion for egg. Strictly, oolites consist of ooids of diameter 0.25–2 mm: rocks composed of ooids larger than 2 mm are called pisolites. They frequently contain minute fragments of shell or rock and sometimes even decayed skeletons of marine life.

Use as a building stone

Ralph Allen promoted its use in Bath in the early 18th century, including his own mansion at Prior Park, but it was used long before then. Example include religious, residential and industrial buildings. The Royal National Hospital for Rheumatic Diseases, which was founded in 1738 was designed by John Wood the Elder was built with Bath stone donated by Ralph Allen. It is a Grade II listed building. There is a fine pediment, in Bath stone, on the building depicting the parable of the good Samaritan.

St Stephens church situated on Lansdown Hill in Bath was constructed from a limestone sourced from the Limpley Stoke mine which is situated in the Limpley Stoke Valley. It has recently been restored.

The material has also been used widely outside of Bath itself. Claverton Pumping Station at Claverton which was built of Bath Stone around 1810, pumps water from the River Avon to the Kennet and Avon Canal using power from the flow of the River Avon. The stone was also used for the Dundas Aqueduct, which is long with three arches built of Bath Stone, with Doric pilasters, and balustrades at each end.

Much of Bristol Cathedral was built of Bath Stone and the Wills Tower, which is the dominant feature of the Wills Memorial Building, is reinforced concrete faced with Bath and Clipsham stone. Bristol's Cabot Tower was also faced with Bath Stone. Arno's Court Triumphal Arch was built from Bath stone around 1760 and later dismantled before being moved to its current location and rebuilt.

Bath Stone was also favoured by architect Hans Price who designed much of 19th century Weston-super-Mare.

In London the neo-classical Georgian mansion Lancaster House was built from Bath Stone in 1825 for the Duke of York and Albany, the second son of King George III. The brick of Apsley House was fronted with Bath Stone, and several churches including Church of Christ the King, Bloomsbury were built from the material.

In Barnstable the 1855 construction of Butchers Row used Bath Stone.

In Reading the original building Royal Berkshire Hospital of 1839, together with the wings added in the 1860s, are now listed grade II* by English Heritage. They are built of Bath Stone with slate roofs, and the main building comprises 2 storeys and a basement. The frontage has 11 bays, with the central 7 bays forming a projecting pedimented hexastyle portico with Ionic columns. In 1860 the nearby Reading railway station building, in Bath Stone and incorporating a tower and clock, was constructed for the Great Western Railway, who also used it for Chippenham railway station.

Other mansions which have used Bath Stone include: Gatcombe Park, Goldney Hall, Tyntesfield, South Hill Park, Spetchley Park.

In 2002 the East End of Truro Cathedral was completely renovated and restored with some of the ornate Bath stone replaced with harder wearing Syerford stone. In 2005 the West Front was restored similarly. Both projects were supervised by MRDA Architects of London, the Cathedral architects.

Quarries

Bath Stone was mined underground at Combe Down and Bathampton Down Mines, in Somerset; and as a result of cutting the Box Tunnel, at various locations in Wiltshire, including Box and Corsham.

Underground extraction of Bath Stone continues in the Corsham area but on a smaller scale than previously. For example, Hanson plc operates Hartham Park Quarry in the Hudswell district (southwest of Pickwick). Other quarries have been re-used. Current examples include primarily defence establishments, but also a wine cellar at Eastlays (near Gastard) and storage for magnetic media (for Off-site Data Protection) at Monk's Park (near Neston).

Non-quarrying re-use of quarries

During the 1930s there was a recognition of a need to provide secure storage for munitions in the south of the United Kingdom, a large area of the quarries around the Corsham area was renovated by the Royal Engineers as one of three major munitions stockpiles. This ammunition depot was serviced by a spur railway line from the main London to Bristol line, breaking away just outside the eastern entrance to Box Tunnel. A portion of the underground quarry complex was developed as an aircraft engine factory, to act as a fallback should the Bristol Engine company Factory at Filton should be taken out of action by hostile bombing. In practice this factory was never used. Another area of the quarry Royal Air Force Box was established as the Headquarters of No10 Fighter Group, Royal Air Force. RAF Box was later renamed RAF Rudloe Manor and expanded to encompass a number of communications functions including No1 Signal Unit, Controller Defence Communications Network, No1001 Signal Unit Detachment and Headquarters RAF Provost & Security Service. No1SU and CDCN were both housed in bunkers within the quarry complex, which also included an RAF Regional Command Centre for the South West of England. Corsham Computer Centre was built into Hudswell Quarry during the 1980s.

British defence doctrine during the early Cold War period indicated a requirement for a fallback location for central government outside London, to assume national control in the event of London being destroyed. The quarry complex at Corsham was chosen for this location and development of the site commenced in the 1950s. In the event of imminent nuclear attack, it was assumed that the government would be evacuated from London by rail or helicopter. The facility would provide a safe haven for the Prime Minister, the Cabinet, commanders of the Royal Air Force, Royal Navy, and British Army and supporting civil servants and military personnel. Facilities inside the complex included accommodation and catering for nearly 4,000 people, including a hospital, organic electrical generation and the ability to seal the complex from the outside environment, contaminated by radiation or other threat.

The defence facilities known as Hawthorn and various code name including; Stockwell, Turnstile and Burlington have been built in quarries include Military Command & Control, storage and a fallback seat of national government. Some areas of the quarry complex were hardened and provided with support measures to ensure resilience in the event of a nuclear attack. The site was decommissioned and placed in a state of care & maintenance in the mid 1990s following the fragmentation of the Soviet Union and the end of the cold war. The site has been offered for sale, conditional on a Private Finance Initiative for the continued use of above ground facilities.

Box Mine

The Box Mine consists of a network of tunnels, which originate from stone mining work, initially started during the Roman occupation of Britain. The mine has now been taken over by bats. Up to 10% of the total British population of greater horseshoe bat uses the mine at times; a maximum of 230 individuals of this species have been counted at the site. Lesser Horseshoe Bat also uses the mine, as do the four Myotis species - Whiskered, Brandt's, Natterer's and Daubenton's bats.

Combe Down and Bathampton Down Mines

Combe Down and Bathampton Down Mines date from the 17th and 18th century when stone was extracted by the "room and pillar" method, by which chambers were mined, leaving pillars of stone between them to support the roof. The mine contains a range of mine features including well preserved tramways, cart-roads and crane bases. The walls and pillars of the mine are studded with pick and tool marks and show evidence of the use of huge stone saws, all of which bear testimony to the variety of techniques used to extract the stone over the mine's three hundred year history. No mine abandonment plans of - either the tunnels or the caverns, known as voids - were made prior to the 1872 Mining Act.

Following their closure were used for a variety of purposes, including a mushroom farm and as an Air-raid shelter during the World War II Baedeker raids on Bath. During 1989 a utilities contractor unexpectedly broke through into part of the mines complex whilst excavating a trench, which raised concerns locally which resulted in the then Bath City Council commissioning studies to survey the condition of the mines. It was clear that the mines were in a very unstable state and some experts considered them to be the largest shallowest and most unstable of their kind in Europe. Approximately 80% of the mines, which are up to high and cover a total area of about , had less than cover and as little as in some places.

In March 1999, the then Department of Environment, Transport and Regions (DETR), now known as the Department for Communities and Local Government, announced a Land Stabilisation Programme, based on the Derelict Land Act 1982. A Parliamentary Statutory Instrument (2002 No. 2053) was needed before the work could be undertaken. Foamed concrete has been selected as the solution for the large scale infilling of the old mine works. It is planned that over of foamed concrete will be placed in the shallow underground mines, making it the single largest application of foamed concrete on a project in the United Kingdom.

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