510 STKATIGEAPHICAL GEOLOGY 



The same zones with a total thickness of about 1000 feet are 

 found in Dorset, where Mr. Eowe has recently identified the zone of 

 Marsupites and has been able to separate the zone of Act, quadratus 

 from that of Bel. mucronata, assigning a thickness of 354 feet to 

 the former and not less than 250 to the latter, 24 the characteristic 

 fossils of the one being Actinocamax granulatus, Act. quadratus, and 

 Offastcr pilula, while those of the higher zone are Belemnitella 

 mucronata, B. lanceolata, Cardiaster ananchytis, Magas pumihis, 

 Crania costata, and Rhynchonella Umbata. 



In Wiltshire and all along the inland outcrop from Salisbury 

 Plain to Suffolk the Micraster zones are exposed in numerous chalk 

 pits and the higher zones are all present in South Wiltshire, but 

 north of the Vale of Pewsey the zone of Bel. mucronata does not 

 occur, and that of Act. quadratus is gradually cut out by the pre- 

 Tertiary planation, till the Eocene comes to lie on the Marsupites 

 zone. 



In all these counties the lower part of the Hoi. planus zone 

 consists of several beds of very hard compact chalky limestone, 

 generally of a creamy colour, and each bed having a layer of 

 calcareo-phosphatic nodules at the top. This limestone is known as 

 " The Chalk Rock " ; above it there is from 15 to 20 feet of greyish 

 nodular chalk consisting of hard lumps embedded in a soft matrix. 

 The total thickness of the zone seldom exceeds 26 feet, so that it 

 may be regarded as a condensed equivalent of the more expanded 

 zone to the south. 



The Chalk rock frequently contains grains of glauconite and is 

 often full of fossils, among which Gastropods are noticeable, for 

 these are rarely found either in Middle or Upper Chalk. The 

 most characteristic fossils are Pachydiscus peramplus, Prionocyclus 

 Neptuni, Scaphites Geinitzi, Heteroceras reussianum, Turbo Geinitzi, 

 and Solariella gemmata. Holaster planus, Micraster precursor, and 

 M. Leskei are also common. 



The zones of M. cortestudinarium and M. coranguinum have 

 the same characters and fossils as in the South Coast sections, as 

 have also the higher zones as far as they can be traced, except in the 

 case of the Marsupites zone which in Berkshire and the Thames 

 Valley presents some peculiar features ; for it contains two beds of 

 brown phosphatic chalk, one at the base of the Uintacrinus band and 

 one at the base of the upper division. These beds are well exposed 

 in the large quarry at Taplow near Maidenhead, where the upper 

 bed is 8 feet thick. The phosphatic matter is in the form of 

 grains, some of which are casts of Foraminifera and others are 

 phosphatised portions of Inoceramus shells. 



In Suffolk and Norfolk the higher zones come in again from 



