Bradford Clay in geology

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

, is a thin, rather inconstant bed of clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

 or marl

Marl

Marl or marlstone is a calcium carbonate or lime-rich mud or mudstone which contains variable amounts of clays and aragonite. Marl was originally an old term loosely applied to a variety of materials, most of which occur as loose, earthy deposits consisting chiefly of an intimate mixture of clay...

 situated in 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...

  at the base of the Forest Marble, the two together constituting the Bradfordian group in the Bathonian

Bathonian

In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma...

 series of 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...

 rocks. The term "Bradford Clay" appears to have been first used by J. de. C. Sowerby in 1823 as an alternative for W. Smith's, "Clay on Upper Oolite". The clay came into notice late in the 18th century on account of the local abundance of the crinoid Apiocrinus Parkinsoni. It takes its name from Bradford-on-Avon in 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...

, whence it is traceable southward to the 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...

 coast and northward towards Cirencester

Cirencester

Cirencester is a market town in east Gloucestershire, England, 93 miles west northwest of London. Cirencester lies on the River Churn, a tributary of the River Thames, and is the largest town in the Cotswold District. It is the home of the Royal Agricultural College, the oldest agricultural...

. It may be regarded as a local phase of the basement beds of the Forest Marble, from which it cannot be separated upon either stratigraphical or paleontological grounds. It is seldom more than 10 feet thick, and it contains, as a rule, a few irregular layers of limestone

Limestone

Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

 and calcareous

Calcareous

Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...

 sandstone

Sandstone

Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

. The lowest layer is often highly fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

iferous; some of the common forms being Arca minuta, Ostrea gregaria, Waldheimia digona, Terebratula coarctata and Cidaris bradfordensis.