310 THE TRANSFORMATION'S OF THE ANIMAL WORLD 



between the various continents of the Earth, it is 

 necessary first to take a bird's-eye view of the general 

 features of the geography of Tertiary times. These 

 shields, to use the picturesque expression of Ed. 

 Suess, are distributed as follows. Three in the 

 Northern Hemisphere, to wit, the Canadian shield, 

 which includes a good part of the United States ; 

 the Scandinavian shield, including, besides Finland, 

 the Russian tableland, the north part of the British 

 Isles, and extending, at certain points, as far as the 

 Ardennes and the expanse of the Rhine ; and, 

 finally, the Sino-Siberian shield, or Angaran con- 

 tinent. In the Southern Hemisphere, the Brazilian 

 continent, the continent of Africa, Madagascar 

 and the neighbouring islands, the Indian peninsula, 

 and Australia constitute so many solid nuclei 

 which have, in a great measure, withstood the 

 invasion of the Tertiary seas and acted in the same 

 manner as the shields of the Northern Hemisphere. 

 To this enumeration must be added a great Ant- 

 arctic polar continent, the Antarctic. 



The history of Tertiary times may be summed up 

 as a series of connections followed by phases of 

 separation of these early nuclei under the influence of 

 the phenomena of the wrinkling or of the subsidence 

 of the earth's crust, and of the marine incursions 

 and retreats which were their consequences. It is, 

 therefore, quite natural that terrestrial animals 

 should have availed themselves of these temporary 

 bridges between continents, to spread afar, by 

 means of reciprocal changes, genera and families 

 till then restricted to a single region only. 



We are still a long way from being able to write 



