608 STRATIGKAPHICAL GEOLOGY 



The change from the conditions of Lower Pliocene to those 

 of Middle Pliocene (or Astian) time seems to have been produced 

 by a general uplift of what may be termed the central axis of 

 Europe, in other words, across the whole of that part of Europe 

 which lies between the parallels of 40 and 51 ; while further 

 subsidence took place both in the southern Mediterranean and 

 also in the northern region. Thus the Italian area continued 

 to sink, permitting a great thickness of marine deposits to be 

 accumulated, and the Pontian lakes continued to exist, but probably 

 they had shrunk in size. The whole of France and the English 

 Channel became dry land, and all direct communication between 

 the Atlantic and the Belgian Sea was thus cut off ; but farther 

 north subsidence was taking place, forming and widening a channel 

 between Scotland and Norway which opened into the Arctic 

 Ocean. 



The facts which relate to this gradual formation of the North 

 Sea Basin and to the extension of the great delta of the Rhine 

 may be mentioned more fully. Having regard to the present 

 position of the Lenham Beds, and the progressive overlap of the 

 newer crags toward the north, as well as the great thickness of the 

 Pliocene deposits in Holland, we may infer that the crust move- 

 ment in the Anglo-Belgian area had the effect of a tilt, which 

 caused a subsidence on its northern side, while its southern Border 

 was raised through at least 780 feet. 



Thus all connection with more southern seas was severed. 

 On the other hand, the subsidence to the northward allowed the sea 

 to spread farther north than in the earlier part of the period, and 

 before the epoch of the Newbourn and Butley Crags it would 

 seem that part of the land which had hitherto united Scotland 

 and Scandinavia was submerged, so that an opening was formed into 

 the Arctic Ocean. 



The Red Crag is generally regarded as a shore deposit, and by 

 Mr. Harmer it is compared with the shelly banks and beaches 

 which are now being formed all along the coast of Holland. These 

 accumulations of sand and shells are attributed by Dutch geologists 

 to the prevalence of gales from the west, and as no such shell-beds 

 exist now on our eastern coasts this seems to explain the facts, but 

 if such was the origin of the Red Crag we must suppose that in 

 Pliocene time the prevalent gales were from the eastward and not 

 from the westward, as is now the case. 26 



As the sea extended its area northward and the land rose 011 its 

 southern border, the valley of the Rhine must have prolonged 

 itself northward over the southern part of the North Sea plain, 

 and we have seen .(p. 600) that the Chillesford Beds may possibly 



