PRELIMINARY CONSIDERATIONS. 65 



influence. The principal climatic disturbance is 

 generally supposed to have been the so-called " Ice 

 Age." So firmly rooted is the conviction, among 

 naturalists of the present day, of the enormous 

 destruction which this period produced on our 

 European fauna, so that all animal life practically 

 disappeared from large areas of our continent, that 

 it is desirable that we should now shortly review 

 the history of that remarkable period in order to 

 ascertain in how far these views are corroborated 

 by facts. Frequent reference, moreover, will be 

 made throughout this work to the theories con- 

 nected with the Glacial period. 



It has been stated by an eminent geologist that 

 during part of the Glacial period the climate was such 

 that neither plants nor animals could have existed in 

 the British Islands. If that had been so, it is evident 

 that very few organisms could have even survived in 

 France, though a number of Arctic species might 

 have dragged on an existence in Southern Europe. 

 At any rate, on the return of more genial conditions, 

 the Arctic species would undoubtedly have been the 

 first to gain admission to the British Islands, to 

 re-people the arid wastes. Our supposition that the 

 Lusitanian element in the British fauna is the oldest 

 would therefore be wrong. From early Tertiary 

 times onward, the climate of Europe, which was 

 then semi-tropical, gradually became more and more 

 temperate; until finally the Ice Age or Glacial 

 period arrived, during which, according to Professor 



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