200 THE ANTIQUITY OF MAN 



thick sheet of ice, flowing more or less radiately 

 outwards from a central region situated in and 

 about the region of Hudson Bay (Sollas, p. n). 

 As to the extent of the American sheet of ice, it 

 is stated that the area covered was fully double 

 that in Europe, amounting to about four million 

 square miles ; while its depth is variously esti- 

 mated to have been from one to three miles. The 

 ice certainly was more than one mile deep over 

 New England, for marks of the movement are 

 found on the summit of Mount Washington, 

 which is more than six thousand feet high (Wright 

 G. F., p. 162). 



The duration of this period will be considered 

 further on ; meantime it may be stated that it 

 is tolerably generally* agreed that the Ice Age 

 was not one of uniform and continuous cold. On 

 the contrary, there were warmer intervals during 

 which the enormous glaciers receded and por- 

 tions of the earth till then locked up under arctic 

 conditions became once more habitable by man 

 and other mammals. This is not to say that all 

 the ice disappeared, but that conditions more 

 or less approximated to those which now exist. 

 Indeed, since we know nothing really about the 

 cause of the Ice Age, and as we are obviously 

 now existing in a genial period, there is nothing 

 to prove that it may not be merely an " inter- 

 val," and that a fifth Glacial Period may not 

 come upon this earth and wipe all the civilisation 



* But not unanimously, for whilst some admit but one inter- 

 glacial epoch, others doubt even that. See Lamplugh Address, 

 Sect. C, Brit. Assoc., 1906. 



