Neocomian

Neocomian, from Neocomum, the Roman name of Neufchatel, in Switzerland, is the name applied to the lower division of the Cretaceous system (q.v.), it being well developed in that district. It is there represented by several hundred feet of marls and massive limestones, the latter including the Caprotinenltalh, containing Caprotina and other Hippuritidaa (q.v.), the Brgozoenhalli, containing polyzoa, and the Orbitolitenhalh, containing foraminifera. These are all marine; but in England the series is represented by two distinct types of strata, one marine, and the other partly estuarine. The former is represented by the upper part of the Speeton Clay on the Yorkshire coast, and by the variable Tealby series in Lincolnshire. Besides ammonites (q.v.) characteristic of zones throughout the marine beds, the Middle Neocomian, including the Tealby beds, are characterised by the large scallop Pecten cinctus; and the Upper by the large oyster Exogyra sinuata and by Perna Mulletii. In the southern counties the fresh-water Hastings Sands (q.v.) correspond apparently to the Lower, and the Weald Clay (q.v.) to the Middle Neocomian, whilst conformably above this, and corresponding to the Upper Neocomian, come the marine beds of the Lower Greensand. [Greensand.] Neocomian rocks generally graduate conformably downwards into the Jurassic (q.v.); but are, sometimes at least, separated from the Upper Cretaceous by an unconformity.