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 

 Hurt nations with alternate advance and retreat of the ice. 

 Modern geologists count four glacial epochs covering the 



From Oeiki* ' Th GnM Ice Af*." 



FJM RK ].". Kurnj.r dnriii" tin- Period of Maximum 



period of the Pleistocene (see <|nat'rnary in diagram ). Kl 

 The causes of these great climatic fluctuations which 

 brought about the ice ages are variously explained by 

 geologists in accordance with three hypotheses. 16 In the 

 course of these ice ages the glaciers pushed southward 



i Lull, R. 8. "Glacial Man," The Yale Review, vol. 1, N. 8., 1912, p. 

 377. 



"See Chamberlain and Salisbury, Geology, vol. iii, pp. 424-446. 



