460 STRATIGRAPHICAL GEOLOGY 



of Scotland were severed from their original connection with Norway 

 in the Jurassic period, or that any sea flowed between the two 

 areas until the great submergence of the Cretaceous period. 



The Corallian episode probably indicates a pause in the sub- 

 sidence or a diversion by some other means of the mud-bearing 

 currents, so that for a time they did not pass over Southern or 

 Northern England though they continued to traverse the intervening 

 space. But matters reverted to their former condition in 

 Kimeridgian time, and the geographical arrangement of land and 

 sea must have continued to be practically the same. 



The Portlandian deposits, however, give evidence of a great 

 change and of a reverse movement by which the sea-floor was 

 shallowed over the whole of Northern and Western Europe, large 

 parts of it being once more raised into dry land. Thus a western 

 land was formed again in the North Atlantic which included the 

 greater parts of Britain, France, and Spain ; the Anglo-Belgian 

 island again came into existence, and was only separated from the 

 western land by a narrow strait running through the counties 

 of Bedford, Huntingdon, and Cambridge. 



The Boreal Jurassic Sea must have retreated northward, but 

 for a time there still remained an arm or gulf extending from 

 Germany across the North Sea area into Yorkshire and Lincoln- 

 shire, but the later Portland and Purbeck deposits of Hanover show- 

 that this gulf was shallow and was soon converted into a plain 

 with lagoons and freshwater lakes. 



Southern Europe was much less affected by this Portlandian 

 and Purbeckian elevation, and marine limestones continued to be 

 formed in a southern (Tithonian) sea which was nearly as extensive 

 as it had been in Oxfordian and Corallian times. From this sea a 

 gulf extended through the east of France and across the Parisian 

 plain to terminate in the estuarine lagoons wherein the English 

 Purbeck Beds were deposited. 



The final phase of Jurassic geography was the establishment of 

 a North Atlantic and North European continent, and the gradual 

 transformation of the Purbeck lagoons into the Wealden lake by 

 the continued uprise of the whole surrounding region. 



In conclusion, reference should be made to Neumayr's theory 

 that there is evidence of the existence of climatic zones in Upper 

 Jurassic time. 26 From the brief review of European deposits which 

 has been given on pp. 451 to 455, it will be seen that they can be 

 grouped under three different facies: (1) a Mediterranean or Alpine; 

 (2) a more northern facies found in Germany and Poland, in 

 Northern France, and in England ; (3) a Boreal facies occurring in 

 the north of Russia, Spitzbergen, and Greenland. Neumayr has 



