11 IK CRETACEOUS SYSTEM 511 



beneath the Eocene and include the highest zone found in England, 

 that of Ottrea lunata. A change also takes place in the zone of 

 Holaster planus, for in Norfolk it passes into hard white chalk with 

 dark -grey flints, without any rocky or nodular beds. 



The following is a tabular view of the Upper Chalk of Norfolk, 

 but the thicknesses of the zones are only approximate : 



Itofc 

 Zone of Ostrea lunata. White with beds and patches of grey chalk. 



Ter. gracilis, Tfiecidium vermiculare, Trigonosemus elegans, 



and many Bryozoa ......... 110 



/.OIK- of Bel. mucronata. Soft white chalk with many Hints, some 



very large and cup-shaped ..... probably 250 

 /ours of Act. quadratus and Marsupites. Not yet separated from 



the zones above and below, Act. granulatus common . probably 400 

 Zones of M. coranguinum and M. cortestudinarium. Chalk with 



many flints, both nodules and courses ..... 340 

 Zone of Hoi. planus (as above described) ...... 50 



1150 



The Upper Chalk of Yorkshire, as exhibited in the cliffs at and 

 near Flamborough Head, has been the subject of special study first 

 by Mr. Lamplugh and more recently by Mr. Eowe, 25 from whose 

 account the following re"sum is taken : 



Feet. 

 Zone of Act. quadratus. Chalk without flints, partly seen in the 



cliffs near Sewerby and partly inland ..... 330 

 Zone of Marsupites, in two bands, without flints .... 208 

 Zone of M. coranguinum, the upper part flintless, the lower with 



many flints and marl seams ....... 260 



Zone of M. cortestudinarium. Hard chalk with many flints . .120 

 Zone of Hoi. planus. Hard chalk with grey flints, both nodules 



and in continuous courses ....... 125 



1043 



With regard to its fossils the Chalk of Yorkshire differs con- 

 siderably from that of Southern and Central England. Thus, 

 Holaster planus being just as common in the zone of Ter. lata as 

 in its own zone, one has to rely on its association with Echinocorys 

 vulgaris for the recognition of the latter. The zone of M. cortestu- 

 dinarium yields the usual assemblage, but in the overlying zone 

 M. coranguinum is a rare fossil and its place is taken by Infulaster 

 rostratus. Again no specimen of Actinocamax quadrat as has been 

 found in Yorkshire, and, Offaster pilula being also rare, the zone 

 finds a local index in Inoceramus lobatus ( = lingua auct, non 

 Goldf.). It is also characterised by the abundance of fossil sponges 

 belonging chiefly to the genera Bolospongia, Scytalia, Seliscothon, 

 Siphonia, Heterostinia, Pachastrella, Phymatella and Verruculina, 

 most of which do not occur in the south of England. 



