CORNBRASH  , in

geology, the name applied to the uppermost member of the Bathenian stage of the Jurassic formation in England . It is an old English agricultural name applied in Wiltshire 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 by William Smith for a thin band of shelly limestone which, in the south of England, breaks up in the manner indicated . Although only a thin group of rocks (10–25 ft.), it is remarkably persistent; it maybe traced from Weymouth to the Yorkshire coast, but in north Lincolnshire it is very thin, and probably dies out in the neighbourhood of the Humber . It appears again, however, as a thin bed in Gristhorpe 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 dark shales in many places—the so-called " clays of the Cornbrash," with Avicula echinata . The Cornbrash is a very fossiliferous formation; the .fauna indicates a transition from the Lower to the Middle Oolites, though it is probably more nearly related to that of the beds above than to those below . Good localities for fossils are Radipole near Weymouth, Closworth, Wincanton, Trowbridge, Cirencester, Witney, Peterborough and Sudbrook Park near Lincoln . A few of the important fossils are; Waldheimia lagenalis, Peden levis, Avicula echinata, Ostrea flabelloides, Myacites decurtatus, Echinobrissus dunicularis; Macrocephalites macrocephalus is abundant in the midland counties but rarer in the south; belemnites are not known . The remains of saurians (Steneosaurus) are occasionally found . 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 York-shire it is a rubbly, marly, frequently ironshot oolitic limestone . In Bedfordshire it has been termed the Bedford limestone .

See JURASSIC; also H . B .

Woodward, "The Jurassic Rocks of Britain," vol. iv . (1894) ; and C . Fox Strangways, vol. i.; both Memoirs of the Geological Survey . (J . A .