| Cornbrash Formation | |
|---|---|
| Stratigraphic range:Bathonian-Callovian168–164 Ma | |
 Cornbrash Formation at Shorncote Quarry inGloucestershire | |
| Type | Geological formation |
| Unit of | Great Oolite Group |
| Underlies | Kellaways Formation,Cayton Clay Formation |
| Overlies | Forest Marble Formation,Blisworth Clay Formation,Scalby Formation |
| Thickness | 0-10.5 m |
| Lithology | |
| Primary | Limestone |
| Location | |
| Region | England |
| Country | United Kingdom |
| Extent | Dorset coast toYorkshire coast |
TheCornbrash Formation is aMiddle Jurassic geologicalformation in England. It ranges in age fromBathonian toCallovian, the uppermost part of the Middle Jurassic.[1]Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specificgenus.[2] The name Cornbrash is an old English agricultural name applied inWiltshire to a variety of loose rubble or brash which, in that part of the country, forms a good soil for growing corn. The name was adopted byWilliam Smith for a thin band of shellylimestone which, in the south of England, breaks up in the manner indicated. Although only a thin group of rocks (10–25 feet c. 3–7 m), it is remarkably persistent; it may be traced fromWeymouth to theYorkshire coast, but innorth Lincolnshire it is very thin, and probably dies out in the neighborhood of theHumber. It appears again, however, as a thin bed inGristhorpe Bay,Cayton Bay,Wheatcroft,Newton Dale and Langdale. In the inland exposures in Yorkshire it is difficult to follow on account of its thinness, and the fact that it passes up into darkshales in many places the so-called clays of the Cornbrash, withAvicula echinata. The Cornbrash is of little value for building or road-making, although it is used locally; in the south of England it is not oolitic, but in Yorkshire it is a rubbly, marly, frequently ironshot oolitic limestone. InBedfordshire it has been termed theBedford limestone.[3]
The Cornbrash is a veryfossiliferous formation; the fauna indicates a transition from the Lower to the MiddleOolites, though it is probably more nearly related to that of the beds above than to those below. Good localities for fossils areRadipole nearWeymouth,Closworth,Wincanton,Trowbridge,Cirencester,Witney,Peterborough andSudbrook Park nearLincoln. A few of the important fossils are:Waldheimia lagenalis,Pecten levis,Avicula echinata,Ostrea fiabelloides,Mycicites decurtatus,Echinobrissus clunicularis.Macrocephalites macrocephalus is abundant in the midland counties but rarer in the south;belemnites are not known.[3] Indeterminatestegosauriandinosaur material (sometimes known under theLexovisaurus) have been discovered in this formation. The teleosaurid crocodyliformesYvridiosuchus,Seldsienean,Clovesuurdameredeor andDeslongchampsina are known from the formation.[4]
This article incorporates text from a publication now in thepublic domain: Chisholm, Hugh, ed. (1911). "Cornbrash".Encyclopædia Britannica. Vol. 7 (11th ed.). Cambridge University Press. p. 163. | This article about a specificstratigraphicformation in the United Kingdom is astub. You can help Wikipedia byadding missing information. |
