THE ARRIVAL OF MAN IN EUROPE 



gradually becoming less severe; and upon this 

 would ensue another period of 10,500 years, 

 during which the climate would grow more and 

 more equable for 5250 years, thenceforward 

 gradually increasing again the differences be- 

 tween summer and winter ; and in a period of 

 160,000 years such 2i,ooo-year cycles would 

 naturally occur nearly eight times. So that, 

 upon a geological survey of what is called the 

 Glacial epoch, we might expect to find an alter- 

 nation of severe and mild climates in Europe, 

 an alternation of epochs in which Britain 

 was inhabited by the hippopotamus with epochs 

 in which the reindeer roamed to the south of 

 France. And this is, in fact, what we do find. 

 It is not long since the Glacial period in Eu- 

 rope was supposed to have been one long, 

 monotonous period of extreme cold ; but now 

 the foremost geologists such as Mr. James 

 Geikie, who has more than any one else illus- 

 trated this subject have discovered at least 

 four or five alternations of warm and cold pe- 

 riods in Europe during the Glacial epoch ; and 

 with further and more minute research we may 

 expect the agreement between observation and 

 deduction to become still more convincing. 



Enough has now been said to give the reader 



some idea of the magnificent line of reasoning 



by which Mr. Croll has unfolded the causes of 



the Glacial period. And it also becomes appar- 



57 



