Corallian Limestone is a coralliferous sedimentary rock, laid down in Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 times. It is a hard variety of "coral rag

Coral rag

Coral rag is a rubbly limestone composed of ancient coral reef material. The term also refers to the building blocks quarried from these strata which are an important local building material in areas such as the east African coast and the Caribbean basin .It is also the name of a member — the Coral...

". Building stones from this geological structure tend to be irregular in shape. It is often found close to seams of Portland Limestone (e.g. Abbotsbury

Abbotsbury

Abbotsbury is a large village and civil parish in the West Dorset district of Dorset, England; situated north-west of Weymouth. It is located from Upwey railway station and from Bournemouth International Airport. The main road running through the village is the B3157, connecting Abbotsbury to...

 in Dorset

Dorset

Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...

, England

England

England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

). It is a younger limestone than its near-neighbour, the Oolitic

Oolite

Oolite is a 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...

, as found in the Cotswolds

Cotswolds

The Cotswolds are a range of hills in west-central England, sometimes called the Heart of England, an area across and long. The area has been designated as the Cotswold Area of Outstanding Natural Beauty...

, in Gloucestershire

Gloucestershire

Gloucestershire is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn, and the entire Forest of Dean....

.

A ridge of Corallian Limestone rises above the Vale of Avon and the Thames Valley

Thames Valley

The Thames Valley Region is a loose term for the English counties and towns roughly following the course of the River Thames as it flows from Oxfordshire in the west to London in the east. It includes parts of Buckinghamshire, Berkshire, North Hampshire, Surrey and west London...

 in its Oxfordshire

Oxfordshire

Oxfordshire is a county in the South East region of England, bordering on Warwickshire and Northamptonshire , Buckinghamshire , Berkshire , Wiltshire and Gloucestershire ....

 stretch. The Oxfordshire Corallian ridge is an escarpment

Escarpment

An escarpment is a steep slope or long cliff that occurs from erosion or faulting and separates two relatively level areas of differing elevations.-Description and variants:...

 holding back the hanging valley that is the Vale of White Horse

Vale of White Horse

The Vale of White Horse is a local government district of Oxfordshire in England. The main town is Abingdon, other places include Faringdon and Wantage. There are 68 parishes within the district...

 and its hardness forced the River Thames

River Thames

The River Thames flows through southern England. It is the longest river entirely in England and the second longest in the United Kingdom. While it is best known because its lower reaches flow through central London, the river flows alongside several other towns and cities, including Oxford,...

 to take a wide northern detour, to cut through the low ridge at Oxford

Oxford

The city of Oxford is the county town of Oxfordshire, England. The city, made prominent by its medieval university, has a population of just under 165,000, with 153,900 living within the district boundary. It lies about 50 miles north-west of London. The rivers Cherwell and Thames run through...

. High points along the ridge are Cumnor Hurst

Cumnor Hurst

Cumnor Hurst, also known as Hurst Hill, is a wooded hill in the neighbourhood of the village of Cumnor, Oxfordshire, England. It lies to the north of Boars Hill. In 1974 it was transferred from Berkshire....

 and Wytham Hill. The outcrop known as Headington stone

Headington stone

Headington stone is a limestone from the Headington Quarry area of Oxford, England.- Geology :Around 160 million years ago, during the Late Jurassic period, Britain was located further south and was submerged beneath a subtropical sea. The warm conditions meant that coral reefs could flourish. When...

 was quarried at Headington Quarry

Headington Quarry

Headington Quarry is a residential district of Oxford, England, located east of Headington and west of Risinghurst, just inside the Oxford ring road in the east of the city. To the south is Wood Farm. Today the district is also known colloquially as "Quarry"...

 on the outskirts of Oxford and used for many of the historic University

University of Oxford

The University of Oxford is a university located in Oxford, United Kingdom. It is the second-oldest surviving university in the world and the oldest in the English-speaking world. Although its exact date of foundation is unclear, there is evidence of teaching as far back as 1096...

 buildings there.

Hilly outcrops above this corallian ridge, composed of Lower Greensand

Greensand

Greensand or Green sand is either a sand or sandstone, which has a greenish color. This term is specifically applied to shallow marine sediment, that contains noticeable quantities of rounded greenish grains. These grains are called glauconies and consist of a mixture of mixed-layer clay...

, occur at Badbury Hill

Badbury Hill

Badbury Hill is a hill in the civil parish of Great Coxwell near Faringdon in the English county of Oxfordshire. In 1974 it was transferred from Berkshire....

, Faringdon

Faringdon

Faringdon is a market town in the Vale of White Horse, Oxfordshire, England. It is on the edge of the Thames Valley, between the River Thames and the Ridgeway...

 (Folly Hill) and Boars Hill

Boars Hill

Boars Hill is a hill hamlet southwest of Oxford, straddling the boundariy between the civil parishes of Sunningwell and Wootton. It was part of Berkshire until the 1974 boundary changes transferred it to Oxfordshire.-History:...

.

Softer sandy deposits occur within the Corallian, found for example at Faringdon, Shellingford

Shellingford

Shellingford, historically also spelt Shillingford is a village and civil parish about south-east of Faringdon in the Vale of White Horse. It was part of Berkshire until the 1974 Local Government Act transferred it to Oxfordshire....

 and Hatford

Hatford

Hatford is a small village and civil parish of some in the Vale of White Horse. It was part of Berkshire until the 1974 boundary changes transferred it to Oxfordshire.-Amenities:...

 in Oxfordshire

Oxfordshire

Oxfordshire is a county in the South East region of England, bordering on Warwickshire and Northamptonshire , Buckinghamshire , Berkshire , Wiltshire and Gloucestershire ....

, where the sands and gravels are extensively quarried.

In England, Corallian Limestone is to be found in Dorset, Wiltshire

Wiltshire

Wiltshire is a ceremonial county in South West England. It is landlocked and borders the counties of Dorset, Somerset, Hampshire, Gloucestershire, Oxfordshire and Berkshire. It contains the unitary authority of Swindon and covers...

, Oxfordshire, Buckinghamshire

Buckinghamshire

Buckinghamshire is a ceremonial and non-metropolitan home county in South East England. The county town is Aylesbury, the largest town in the ceremonial county is Milton Keynes and largest town in the non-metropolitan county is High Wycombe....

, Cambridgeshire

Cambridgeshire

Cambridgeshire is a county in England, bordering Lincolnshire to the north, Norfolk to the northeast, Suffolk to the east, Essex and Hertfordshire to the south, and Bedfordshire and Northamptonshire to the west...

, Lincolnshire

Lincolnshire

Lincolnshire is a county in the east of England. It borders Norfolk to the south east, Cambridgeshire to the south, Rutland to the south west, Leicestershire and Nottinghamshire to the west, South Yorkshire to the north west, and the East Riding of Yorkshire to the north. It also borders...

 and Yorkshire

Yorkshire

Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...

.

The most noted scholar of the Corallian strata of England was the geologist W.J. Arkell

William Joscelyn Arkell

William Joscelyn Arkell M.A.; D.Phil.; D.Sc.; FGS.; FRS. was a British geologist and paleontologist, regarded as the leading authority on the Jurassic Period during the middle part of the 20th century.-Childhood:...

(1904–1958).