CHAP. XIV.] SUMMAET OF GEOGRAPHICAL EVOLUTION. 315 



of the Upper Eocenes (or Nummulitic series) the seas 

 which covered parts of England certainly opened southward 

 into a great southern or Mediterranean sea, whence per- 

 haps we may conclude that the sea of the London Clay 

 had a similar but narrower opening in the same direction. 



In Oligocene time the western and southern European 

 seas were greatly contracted, but a shallow northern sea 

 was gradually formed which extended over south-western 

 Russia, Prussia, Holland, and Belgium, but does not 

 appear to have reached quite so far west as England. 

 There was, however, a smaller and possibly isolated sea, 

 lying over northern France, and receiving the waters of a 

 large river which drained the western part of the British 

 region and had its estuary over Hampshire and the Isle of 

 Wight. 



Even after the early Miocene upheaval, and when subsi- 

 dence again led to the formation of deposits in France and 

 Belgium, the sea seems to have re-occupied portions of the 

 same basins, for the Miocene and early Pliocene beds occur 

 in similar positions and in the same localities as those of 

 Oligocene age. It is true that the sea of the Diestian Sands 

 spread westward into the east of England, and that the 

 precise limits of this sea are very doubtful, but there is no- 

 proof that it had any great northerly extension, or that the 

 belt of land enclosing the Arctic Ocean had as yet been 

 broken through either to the north or east of Scotland. 



But while the eastern and southern portions of the 

 British region were receiving here and there fresh acces- 

 sions of stratified material, a very different process was in 

 operation over the western and northern portions of the 

 same region. There can be little doubt that these districts 

 remained in the condition of dry land throughout the 

 duration of the Eocene, Oligocene, Miocene, and Pliocene 

 periods, and that their surface was profoundly modified by 

 the continued action of rain, frost, and running water. 



