

TI1K CRETACEOUS SYSTKM 



hind. Tlu- lower portion of the series ia often called the Neocomian, 

 from Ni'iirhutfl in Switzerland, where the beds were first studied 

 and described, but this Neocomian has since been subdivided into 

 two parts, the Valenginian and the Hauterivian, whicli seem to have 

 the value of separate stages. The Barremian takes its name from 

 llanvme in the Basses - Alpes, and the Aptian from Apt in 

 Vaucluse. 



The Upper Series includes the Selbornian, to part of whicli tin- 

 French Albian corresponds, and the several stages of the Chalk 

 which have received special names on the Continent, but are in 

 England generally known as the Lower, Middle, and Upper Chalk. 

 The stages recognised in Western Europe are tabulated below and 

 correlated with their British representativea 



W. 'stern Europe. Southern England. Northern England. 



Danian . . . Wanting . . Wanting. 



Senonian . . Upper Chalk . Upper Chalk. 



Turoniau (restricted) Middle Chalk . Middle Chalk. 



Cenoinanian . . Lower Chalk . . Lower Chalk. 



Albian . . . Selbornian . . Red Chalk. 



Aptian . . . Vectian . . . Upper Speeton clay. 

 Barremian } r^-jji < 



Hauteriviant . Wealden . . (Middle Speeton clay. 

 VKh-nginianJ V Lower Speeton clay. 



The relation of the Cretaceous strata to the underlying forma- 

 tions is an important matter. Throughout the greater part of 

 England there is a marked break and unconformity between the 

 Jurassic and Cretaceous Systems, and even in Yorkshire the 

 apparent conformity is probably deceptive, for there is nothing 

 there which can safely be correlated with the Portlandian, and it 

 is very doubtful whether there is any representative of the 

 Purbeck Beds. It is only in the south of England, where the 

 highest Jurassic Beds are fully developed, that a complete sequence 

 of deposits is found to fill up the gap between the two systems, but 

 these deposits are of freshwater origin and do not bridge over the 

 gap in the marine succession. 



This gap was undoubtedly caused by the elevation of the greater 

 part of the British region into dry land, a land which extended 

 southward into France and eastward through Belgium ; and it was 

 only after a long period of time, marked by the formation of 

 several thousand feet of marine deposits in the south of Europe, 

 that parts of this land were again submerged and that marine 

 deposits were laid down all across England. This change was the 

 commencement of a great subsidence which eventually carried the 

 Cretaceous Seas over the greater part of Europe. 



