20 



THE AGE OF MAMMALS 



the sea were formerly elevated and furnished land bridges or connections 

 between the continents; he thus clearly adumbrated the idea of the migra- 

 tions of quadrupeds and of the subsequent separation of faunas, or animal 

 groups, by continental depressions and the submergence of old migration 



routes. 



The accompanying map, the dotted areas on which represent the land 

 bridges which would emerge through the elevation of the continental 

 borders to a height of two hundred fathoms, shows the reader that no 



Fig. 8. — Map of the world with existing outlines and 200 fathom lines (dotted areas) 

 showing former land connections at the last period of maximum elevation. 



very profound or cataclysmal changes are required to connect the northern 

 continents with each other and wth the outlying masses. With the south- 

 ern continents, South America, Africa, and Australia, it is different; an 

 emergence of 3040 meters, or 1662 fathoms, is necessary to connect them 

 as shown on the map on p. 77. 



Still more definitely Buffon placed the land separation between the old 

 and new worlds in his "Sixth Epoch," and in this connection clearly brought 

 out a theory of extinction of certain species, as of the mammoths of Sil)eria 

 and of North America. This problem of the interpretation of the giant 

 fossils of the north had been one of the first to attract the attention of 

 naturalists; Johann Georg Gmelin (1709-1755) left it as a legacy to Buf- 

 fon, Buffon handed it down to Blumenbach, the pioneer of vertebrate 

 palaeontology in Germany. Buffon attributed (Tome V, p. 172) the dis- 

 appearance of the great animals from the north partly to the refrigeration 

 of the temperature, and partly to migration to the south. Nous ne pouvons 



