is a coralliferous sedimentary
rock, laid down in Jurassic
times. 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
). It is a younger limestone than its near-neighbour, the Oolitic
, as found in the Cotswolds
, in Gloucestershire
A ridge of Corallian Limestone rises above the Vale of Avon and the Thames Valley in its Oxfordshire stretch. The Oxfordshire Corallian ridge is an escarpment holding back the hanging valley that is the Vale of White Horse and its hardness forced the River Thames to take a wide Northern detour, to cut through the low ridge at Oxford. High points along the ridge are Cumnor Hurst and Wytham Hill.
Hilly outcrops above this corallian ridge, composed of Lower Greensand, occur at Badbury Hill, Faringdon (Folly Hill) and Boars Hill.
Softer sandy deposits occur within the Corallian, found for example at Faringdon, Shellingford and Hatford in Oxfordshire, where the sands and gravels are extensively quarried.
In England, Corallian Limestone is to be found in Dorset, Wiltshire, Oxfordshire, Buckinghamshire, Cambridgeshire, Lincolnshire and Yorkshire.