236 THE CHAIN OF LIFE. 



My own conclusions, which I have advocated elsewhere,^ and 

 which are based on extensive study of the northern parts of 

 America, where the deposits of this age are more widely 

 developed than elsewhere, are that there was one great subsi- 

 dence, leading to a condition in which the lower levels of the 

 continents were covered with ice-laden water and the higher 

 regions were occupied with permanent snow and glaciers. This 

 submergence went on till even high mountains 4,000 feet or 

 more in elevation were under water. Then there was a gradual 

 though intermittent elevation, during which the climate became 

 ameliorated, and lastly there was a condition in which the land 

 of the northern hemisphere stood higher than at present, and 

 which immediately preceded the modern period. As these con- 

 ditions have great significance with reference to the appear- 

 ance of man, I have tabulated them for reference as they occur 

 in Scandinavia, Great Britain, and North America. The so- 

 called " Interglacial Periods " of some geologists are in reality 

 local results of the stages of intermittent elevation in which 

 were deposited beds which in some cases, as m Scotland, 

 Sweden, and Eastern Canada, hold sea-shells, and in others, 

 as in the central areas of North America, contain remains of 

 plants of northern species. 



We shall name, for convenience, the parts of this Pleistocene 

 revolution which include the great subsidence and glaciation, 

 the Glacial Age, that extending from the re-elevation to the 

 modern the Post-glacial. 



The Glacial Age proved fatal to a large proportion of the 

 land life of the previous periods. According to Professor Boyd 

 Dawkins, out of fifty-three species known in Britain in the 

 Post-glacial, only twelve are survivors of the Pliocene; and 

 probably the proportions would not be greater in any part of 

 the northern hemisphere. Some, however, did survive, either 

 by migrating southward or by being inhabitants of places 

 less severely affected than most by the general cold and 



* Notes on Post-Pliocene of Canada ; Acadian Geology^ 3rd edition. 



