CHAPTER X. 



THE CRETACEOUS PERIOD. 



IN the south of England, where the highest Jurassic beds 

 are fully developed, there is a complete sequence 

 through the freshwater Purbeck and Wealden groups to 

 marine deposits of Cretaceous age ; but elsewhere through- 

 out Britain and the north of France the marine deposits of 

 the two systems are separated by a marked break and un- 

 conformity, representing the interval during which the 

 older rocks were upheaved and remained in the condition 

 of dry land. 



In the south of France this gap is filled by a complete 

 series of marine deposits, which are known as the Neocomien 

 and Urgonien groups, and these, therefore, are the marine 

 equivalents of our Wealden series. In Yorkshire and 

 Lincolnshire also the freshwater series is partially repre- 

 sented by marine deposits, some of which are probably as 

 old as the upper part of the French and Swiss Neocomian, 

 but there is still an unconformity at their base. The 

 following is a tabular view of the members of the Creta- 

 ceous system in the south and north of England respec- 

 tively, with the names of their French equivalents ; the two 

 lower stages of the English succession being grouped as the 

 Lower Cretaceous series, and the four upper constituting 

 the Upper Cretaceous series. 





