The Corallian Group or Corallian Limestone is a geologic group in

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

. It is predominantly a coralliferous

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

rock, laid down in the Oxfordian stage of the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

. It is a hard variety of " coral rag". 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 in

Dorset Dorset ( ; Archaism, archaically: Dorsetshire , ) is a Ceremonial counties of England, ceremonial county in South West England. It is bordered by Somerset to the north-west, Wiltshire to the north and the north-east, Hampshire to the east, t ...

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

Cotswolds The Cotswolds ( ) is a region of central South West England, along a range of rolling hills that rise from the meadows of the upper River Thames to an escarpment above the Severn Valley and the Vale of Evesham. The area is defined by the bedroc ...

, in

Gloucestershire Gloucestershire ( , ; abbreviated Glos.) is a Ceremonial counties of England, ceremonial county in South West England. It is bordered by Herefordshire to the north-west, Worcestershire to the north, Warwickshire to the north-east, Oxfordshire ...

. It is laterally equivalent to and interfingers with units of the

Ancholme Group The Ancholme Group is a Group (geology), geological group in England. It preserves fossils dating back to the Jurassic Period (geology), period. It has previously been referred to as the Ancholme Clay Group. The group consists of predominantly gr ...

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

Oxfordshire Oxfordshire ( ; abbreviated ''Oxon'') is a ceremonial county in South East England. The county is bordered by Northamptonshire and Warwickshire to the north, Buckinghamshire to the east, Berkshire to the south, and Wiltshire and Glouceste ...

stretch. The Oxfordshire Corallian ridge is an

escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations. Due to the similarity, the term '' scarp'' may mistakenly be incorrectly used inte ...

holding back the hanging valley that is the

Vale of White Horse The Vale of White Horse is a Non-metropolitan district, local government district of Oxfordshire in England. It Historic counties of England, was historically part of Berkshire. The area is commonly referred to as the 'Vale of ''the'' White Hors ...

and its hardness forced the

River Thames The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, s ...

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

Oxford Oxford () is a City status in the United Kingdom, cathedral city and non-metropolitan district in Oxfordshire, England, of which it is the county town. The city is home to the University of Oxford, the List of oldest universities in continuou ...

. High points along the ridge are Cumnor Hurst and Wytham Hill. The outcrop known as Headington stone was quarried at Headington Quarry on the outskirts of Oxford and used for many of the historic

University A university () is an educational institution, institution of tertiary education and research which awards academic degrees in several Discipline (academia), academic disciplines. ''University'' is derived from the Latin phrase , which roughly ...

buildings there. Hilly outcrops above this corallian ridge, composed of Lower Greensand, occur at

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. The summit of the hill is the site of an Iron Age hill fort known as Badbury Camp. It ...

Faringdon Faringdon is a historic market town in the Vale of White Horse, Oxfordshire, England, south-west of Oxford, north-west of Wantage and east-north-east of Swindon. Its views extend to the River Thames in the north and the highest ground visib ...

(Folly Hill) and Boars Hill. Softer sandy deposits occur within the Corallian, found for example at

, Shellingford and Hatford in

, where the sands and gravels are extensively quarried. The Corallian Limestone

aquifer An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...

is present at outcrop in

Yorkshire Yorkshire ( ) is an area of Northern England which was History of Yorkshire, historically a county. Despite no longer being used for administration, Yorkshire retains a strong regional identity. The county was named after its county town, the ...

and in the

. In Yorkshire it consists of limestones and grits up to about 110 m thick, thinning to about 20 m towards the south of the region, where the limestones are progressively replaced by clay. It is typically well jointed and gives rise to numerous springs. Here it yields up to 15 L/sec. In the Cotswolds the aquifer is up to 40 m thick, give yields of 5 to 10 L/sec, with water quality becoming increasingly saline down dip as the aquifer becomes confined in the

Wessex Basin The Wessex Basin is a petroleum-bearing geological area located along the southern coast of England and extending into the English Channel. The onshore part of the basin covers approximately 20,000 km2 and the area that encompasses the Englis ...

. In England, Corallian Limestone is to be found in

Wiltshire Wiltshire (; abbreviated to Wilts) is a ceremonial county in South West England. It borders Gloucestershire to the north, Oxfordshire to the north-east, Berkshire to the east, Hampshire to the south-east, Dorset to the south, and Somerset to ...

Buckinghamshire Buckinghamshire (, abbreviated ''Bucks'') is a Ceremonial counties of England, ceremonial county in South East England and one of the home counties. It is bordered by Northamptonshire to the north, Bedfordshire to the north-east, Hertfordshir ...

Cambridgeshire Cambridgeshire (abbreviated Cambs.) is a Ceremonial counties of England, ceremonial county in the East of England and East Anglia. It is bordered by Lincolnshire to the north, Norfolk to the north-east, Suffolk to the east, Essex and Hertfor ...

Lincolnshire Lincolnshire (), abbreviated ''Lincs'', is a Ceremonial counties of England, ceremonial county in the East Midlands and Yorkshire and the Humber regions of England. It is bordered by the East Riding of Yorkshire across the Humber estuary to th ...

and

. The most noted scholar of the Corallian strata of England was the geologist W.J. Arkell (1904–1958).

References

External links

* Geological groups of the United Kingdom Geologic formations of England Jurassic England Limestone groups of the United Kingdom Geography of Dorset Jurassic System of Europe Oxfordian Stage {{England-stub

See also

References

External links