DYNAMICAL GEOLOGY. 237 



during the Pleistocene Age is most simply regarded as repre- 

 senting an extreme phase of existing climatic conditions. 



Charpentier thought at first that the glaciation might have 

 been due to the former greater height of the Alpine system ; 

 but he afterwards modified his opinion in so far as he regarded 

 an exceptionally high rainfall in addition to a low temperature 

 as a necessary condition in the accumulation of immense 

 masses of ice. Charpentier argued that the atmosphere must 

 have been loaded with moisture, which became condensed 

 over the high Alpine regions. 



Many attempts have been made to explain the Pleistocene 

 climate, sometimes cosmic causes, sometimes telluric causes 

 being selected as the more important. Sir Charles Lyell 

 ascribed the climates of geological epochs solely to telluric 

 influences (ante^ p. 192). He thought the Ice Age in Europe 

 and North America was explicable upon some such assump- 

 tion as a close grouping of islands round the North Pole, a 

 heightening of the continental territories between 70 and 80 

 latitude, a submergence of the temperate zone below the 

 ocean, and a diversion of the warmth-giving Gulf Stream. 

 Escher von der Linth and Desor brought forward (1863) in 

 support of this theory their conclusion that the Sahara had 

 been totally submerged during Pleistocene time, and that the 

 consequent absence of the warm Fohn wind must have lowered 

 the temperature of Central and Southern Europe. It has since 

 been shown by Dove that the Fohn wind -does not come from 

 the Sahara, and Zittel and other scientific explorers of the 

 Sahara have disproved the old idea that the Sahara was under 

 water during the Pleistocene age. 



The principle involved in LyelPs theory was accepted by 

 Sartorius von Waltershausen and Stanislas Meunier, who 

 assumed a much greater height and breadth of the mountain- 

 systems as the chief modifying cause. Meunier showed that 

 the accumulation of snow and ice on extensive mountain 

 plateaux would of necessity lower the temperature. The 

 Norwegian geologist, K. Pettersen, believed that an Arctic 

 continent existed between Greenland and Spitzbergen during 

 the Ice Age. 



The explanations which have received the widest recognition 

 are, however, based upon cosmic causes. The French mathe- 

 matician, Adhe'mar, in 1832 contributed a remarkable paper 

 on the "Revolution of the Sea: Periodic Deluges." He 



