THE ICE AGE 



century ago suggested that the cold may have been 

 due to the alterations in the shape of the earth's orbit, 

 alterations which astronomers tell us take place regularly, 

 though very slowly and at intervals of millions of years. 

 If so, this glacial period was only the last of many 

 glacial periods ; the traces of the earlier ones having, 

 however, been for the most part obliterated and de- 

 stroyed. 



Sir Charles Lyell has urged that geographical 

 changes (elevations and subsidences) would of themselves 

 be sufficient to bring about a glacial period, which (he 

 says) would be the result of a great continent being 

 formed round the North Pole while oceanic conditions 

 prevailed at the Equator. Another theory is that the 

 heat given out by the sun is not always equal, being 

 sometimes more (when even polar countries enjoy a warm 

 climate) and sometimes less (when only the equatorial 

 regions are habitable). The objection to this theory is, 

 of course, that we have no proof that our sun is of greatly 

 variable heat. Whatever may have been the cause of the 

 glacial period, we know as a proved fact that a long time 

 ago (as measured by years, although the event itself is 

 among the latest of the many changes recorded in the 

 geological history of the earth) the climate of the 

 British Isles was so intensely cold that the greater part 

 of this country was covered with ice and snow, and we 

 know also that this intense cold was sufficient to change 

 in many respects the habits and appearance of the 

 animals and vegetation of the earth. How much this 

 was the case can be gathered from the fact that in the 



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