CHAP. XIV.] SUMMARY OF GEOGRAPHICAL EVOLUTION. 313 



heaval was greater in the western than in the eastern part 

 of the British region, or the later Cretaceous subsidence was 

 deeper in the eastern area ; it is very likely indeed that 

 both movements contributed to the same result, i.e. of re- 

 ducing the whole eastern tract to a lower relative level than 

 it had occupied throughout Jurassic time. 



The early Cretaceous subsidence seems to have been 

 fairly equable, and the Vectian sea does not seem to have 

 encroached much on these eastern uplands, though it is 

 probable that the relative levels of the two areas were so 

 far altered that the sea covered a wider tract on the east 

 and a much narrower one on the west than would have 

 been submerged by a depression of the same vertical extent 

 in Jurassic time. In the succeeding epoch this was cer- 

 tainly the case, and we know that the whole of eastern 

 England sank below the waters of the Gault sea, while 

 there is good reason to believe that this sea did not extend 

 to Wales or over the north-west of England. The subse- 

 quent subsidence, however, was much more extensive ; not 

 only did it bury the remaining portions of the eastern land 

 under a continuous sheet of Chalk, but the western land 

 was converted into an archipelago, and great sheets of chalk 

 and greensand were deposited far beyond the limits of the 

 Jurassic strata over the slopes of the western and northern 

 highlands. 



The chief result of these changes therefore, so far as the 

 geographical evolution of Britain is concerned, was the 

 complete suppression and burial of the rocky land which 

 had previously existed over the areas now occupied by the 

 North Sea and the eastern counties of England. This land 

 has never again been uncovered, and its extent has only 

 been gradually revealed to us by the deep borings which 

 have been made in England, France, and Belgium. Its 

 coverings were indeed repeatedly added to in Tertiary 

 times, while erosion was busy over the rest of England. 



