48 THE GEOLOGICAL EVIDENCES 



genera are identical with the genera of to-day, and 

 even a limited number of living species appear 

 for the first time. One of these is the common 

 hippopotamus, which, consequently, represents 

 about the oldest type of existing quadrupeds. In the 

 Post-Pliocene period the correspondence between 

 the existing and extinct faunas is still further in- 

 creased through the large preponderance of recent 

 species. On the border-line of this and the pre- 

 ceding period we meet with the earliest unequiv- 

 ocal remains of man himself. 



The correspondence between the recent and 

 extinct mammalian faunas may be conveniently 

 summarized as follows : 



Post- Pliocene period. 

 Mammalia principally of living species. 



Pliocene period. 

 Mammalia principally of recent genera living 



species rare. 



Miocene period. 

 Mammalia principally of living families extinct 



genera numerous; species extinct. 



