POST-TERTIARY PERIOD. 535 



Farther north in Europe the flora indicates the warm-temperate 

 climate characterizing the North American Tertiary, and it is also 

 prominently North American in its types. 



The difference in climate between North America and Europe is 

 fully explained if we suppose that in the former after the Creta- 

 ceous period an increase in the extent of the polar lands took 

 place ; for this would have given all the coolness to the climate 

 that the facts require. This is not a mere supposition ; for (1) the 

 elevation of a large part of the continent above the ocean beyond 

 doubt took place at that time (p. 533) ; and (2) no Tertiary rocks 

 have been observed in the Arctic to prove a submergence there in 

 that period, although Post-tertiary beds (proving a later submerg- 

 ence) are widely distributed. The extension of the American con- 

 tinent into the Arctic Zone is a prominent source of the existing 

 difference of climate between it and Europe. 



It is not surprising, therefore, that central North America should 

 have passed at once to a warm-temperate climate, while Europe, 

 although situated in higher latitudes, should have had in succession 

 a tropical, subtropical, and temperate climate. Admitting this ex- 

 planation, we understand why the Eocene plants of America are 

 analogous to the Miocene rather than to the Eocene of Europe. 



II. POST-TERTIARY PERIOD (20). 



Hitherto, through the ages to the close of the Tertiary period, 

 the continent of North America had been receiving a gradual ex- 

 tension to the southward, spreading itself southeastward on the 

 Atlantic side and southwest-ward on the Pacific. The scene of 

 prominent action here changes, and in the Post-tertiary the great 

 phenomena are mainly northern. The same general fact is true for 

 all the continents, north and south : the changes affect most de- 

 cidedly the higher latitudes of the globe. 



The Post-tertiary period in America includes two epochs : — 

 1, The Glacial, or that of the Drift ; 2, the Champlain. Next 

 follows (3) the Terrace epoch, — a transition epoch, in the course 

 of which the peculiar Post-tertiary life ends and the age of Man 

 opens. 



1. GLACIAL EPOCH. 



American. 



Material, Phenomena, and Distribution of the Drift. 

 Drift. — The term Drift, as it is commonly employed in Geology, 

 includes the gravel, sand, or stones, occurring over some parts of 



