The Corallian Group or Corallian Limestone is a

geologic group Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe ...

. It is predominantly a coralliferous

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

rock, laid down in the Oxfordian stage of the

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

. It is a hard variety of "

coral rag Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and secr ...

". 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 is a village and civil parish in the English county of Dorset. The settlement is in the unitary authority of Dorset about inland from the English Channel coast. The village, including Chesil Beach, the swannery and subtropic ...

Dorset Dorset ( ; archaically: Dorsetshire , ) is a county in South West England on the English Channel coast. The ceremonial county comprises the unitary authority areas of Bournemouth, Christchurch and Poole and Dorset. Covering an area of , ...

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

Cotswolds The Cotswolds (, ) is a region in central-southwest England, along a range of rolling hills that rise from the meadows of the upper Thames to an escarpment above the Severn Valley and Evesham Vale. The area is defined by the bedrock of J ...

, in

Gloucestershire Gloucestershire ( abbreviated Glos) 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. The county town is the city of ...

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

Ancholme Group The Ancholme Group is a geologic group in England. It preserves fossils dating back to the Jurassic period. It has previously been referred to as the Ancholme Clay Group. The group consists of predominantly grey, marine mudstone and silty mudst ...

. A ridge of Corallian Limestone rises above the

Vale of Avon A vale is a type of valley. Vale may also refer to: Places Georgia * Vale, Georgia, a town in the Samtskhe-Javakheti region Norway * Våle, a historic municipality Portugal * Vale (Santa Maria da Feira), a former civil parish in the municipali ...

and the

Thames Valley The Thames Valley is an informally-defined sub-region of South East England, centred on the River Thames west of London, with Oxford as a major centre. Its boundaries vary with context. The area is a major tourist destination and economic hub, ...

in its

Oxfordshire Oxfordshire is a ceremonial and non-metropolitan county in the north west of South East England. It is a mainly rural county, with its largest settlement being the city of Oxford. The county is a centre of research and development, primaril ...

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. The terms ''scarp'' and ''scarp face'' are often used interchangeably with ''esca ...

holding back the

hanging valley A valley is an elongated low area often running between hills or mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers or streams over ...

that is the

Vale of White Horse The Vale of White Horse is a local government district of Oxfordshire in England. It was historically a north-west projection of Berkshire. The area is commonly referred to as the 'Vale of ''the'' White Horse'. It is crossed by the Ridgeway Na ...

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, se ...

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

Oxford Oxford () is a city in England. It is the county town and only city of Oxfordshire. In 2020, its population was estimated at 151,584. It is north-west of London, south-east of Birmingham and north-east of Bristol. The city is home to the ...

. High points along the ridge are Cumnor Hurst and

Wytham Wytham ( ) is a village and civil parish on the Seacourt Stream, a branch of the River Thames, about northwest of the centre of Oxford. It is just west of the Western By-Pass Road, part of the Oxford Ring Road ( A34). The nearest village is ...

Hill. The outcrop known as

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 ...

was quarried at

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 colloquia ...

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

University A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United Stat ...

buildings there. Hilly outcrops above this corallian ridge, composed of

Lower Greensand The Lower Greensand Group is a geological unit present across large areas of Southern England. It was deposited during the Aptian and Albian stages of the Early Cretaceous. It predominantly consists of sandstone and unconsolidated sand that were ...

, occur at Badbury Hill,

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. It extends to the River Thames in the north; the highest ground is on the Ridg ...

(Folly Hill) and

Boars Hill Boars Hill is a Hamlet (place), hamlet southwest of Oxford, straddling the boundary between the Civil parishes in England, civil parishes of Sunningwell and Wootton, Vale of White Horse, Wootton. Historically, part of Berkshire until the Local ...

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

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

and

Hatford Hatford is a 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 As Hatford is so small it has almost no amenities. Hatford has no v ...

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

aquifer An aquifer is an underground layer of water-bearing, permeable rock, rock fractures, or unconsolidated materials ( gravel, sand, or silt). Groundwater from aquifers can be extracted using a water well. Aquifers vary greatly in their characte ...

is present at outcrop in

Yorkshire Yorkshire ( ; abbreviated Yorks), formally known as the County of York, is a Historic counties of England, historic county in northern England and by far the largest in the United Kingdom. Because of its large area in comparison with other Eng ...

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. In England, Corallian Limestone is to be found in

Wiltshire Wiltshire (; abbreviated Wilts) is a historic and ceremonial county in South West England with an area of . It is landlocked and borders the counties of Dorset to the southwest, Somerset to the west, Hampshire to the southeast, Gloucestershire ...

Buckinghamshire Buckinghamshire (), abbreviated Bucks, is a ceremonial county in South East England that borders Greater London to the south-east, Berkshire to the south, Oxfordshire to the west, Northamptonshire to the north, Bedfordshire to the north-e ...

Cambridgeshire Cambridgeshire (abbreviated Cambs.) is a county in the East of England, bordering Lincolnshire to the north, Norfolk to the north-east, Suffolk to the east, Essex and Hertfordshire to the south, and Bedfordshire and Northamptonshire to t ...

Lincolnshire Lincolnshire (abbreviated Lincs.) is a Counties of England, county in the East Midlands of England, with a long coastline on the North Sea to the east. It borders Norfolk to the south-east, Cambridgeshire to the south, Rutland to the south-we ...

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 formations Geography of Dorset Jurassic System of Europe Oxfordian Stage {{England-stub

See also

References

External links