CHAP. XIV.] SUMMARY OP GEOGRAPHICAL EVOLUTION. 307 



about the sequence of the great physical changes which 

 ensued in later Carboniferous and in Permian times that 

 we are hardly in a position to take the early Carboniferous 

 geography as the starting point for any connected evolu- 

 tional history of the British Islands. 



To the Carboniferous succeeded a great transitional 

 period, during which immense geographical changes seem 

 to have taken place throughout the northern hemisphere. 

 In Britain this is represented by two great stratigraphical 

 breaks with an intercalated group of peculiar deposits, and 

 opinion is divided whether the greatest physical changes 

 took place before or after the formation of these Permian 

 or Dyassic deposits. For our present purpose we may 

 regard the whole as one period, and the final pre-Triassic 

 movements may be considered as the culminating effort, 

 as it were, of the disturbing forces which had been set in 

 action at the close of the Carboniferous period, and which 

 seem to have acquired unusual power and energy from the 

 state of tension induced by the long antecedent period of 

 quiet accumulation. 



The general result was the formation of a large conti- 

 nental territory over the northern part of the European 

 area, and the platform on which the British Islands stand 

 formed part of this Triassic continent. Not only so, but 

 the regional blocks which form the more salient portions 

 of our islands had already been rough hewn, as it were, 

 and set up in the places which they now occupy to be 

 gradually carved and sculptured during the long Neozoic 

 ages into the forms and features which they now exhibit. 

 The principal hill-ranges of western and northern England, 

 of Ireland, and of Scotland, were then in existence, and 

 bore in most cases the same general relations to the lower 

 ground around them as they do at the present time. 



It is true that the east of England bore a very different 

 appearance from its modern aspect, forming as it then did 



