54 SOCIAL EVOLUTION 



regions once inhabited by cold climate fauna, one finds 

 creatures whose structure and habits show them to have 

 been denizens of warmer lands. There were climatic 

 fluctuations with alternate advance and retreat of the ice. 

 Modern geologists count four glacial e])ochs covering the 



From Geikic "The Great Ice Age." 



FioriiK l.l. I'urope diniiiq- tlio Period of Mnxinium Glaciation. 



period of the Pleistocene (see quaternary in diagram). ^^ 

 The causes of these great climatic fluctuations which 

 brought about the ice ages are variously explained by 

 geologists in accordance with three hypotheses.^^ In the 

 course of these ice ages the glaciers pushed southward 



i^'Lull, R. S.— "Glacial Man," The Talc Review, vol. 1, N. S., 1912, p. 



377. 



16 Sec Chainbcrlain and HaYishury, —Gcolofjij, vol. iii, pp. 424-44G. 



