TERTIAEY PERIOD BY MEANS OF THE MAMMALIA. 381 



Characteristics. 



VI. Historic, in which the events are re- 

 corded in History. 



Historical Kecord. 



V. Prehistoric, in which domestic ani- 

 mals and cultivated fruits appear. 



Man abundant. Domestic ani- 

 mals. Cultivated fruits. 



IV. Pleistocene, in which living species of 

 Placental Mammals are more abun- 

 dant than the extinct. 



Man appears. Living species 

 abundant. 



III. Pliocene, in which living species of 

 Placental Mammals appear. 



Living species appear. 



II, Miocene, in which the alliance be- 

 tween living and Placental Mam- 

 mals is more close than before. 



Living genera appear. 



I. Eocene, in which the Placental Mam- Living Orders and Families ap- 



mals now on the earth were repre- | pear, 

 sented by allied forms belonging to 

 existiug Orders and Families. 



This may be represented by the following diagram :- 



VI. HISTORIC STAGE 



LIVING SPECIZS 

 NO EXTINCT SPECIES 



V. PREHISTORIC 



IV. PLEISTOCENE 



III. PLIOCENE 



II. MIOCENE 



LIVING SPECIES 

 ONE EXTINCT SPECIES 



LIVING SPECIES 

 ABUNDANT 



SEVERAL EXTINCT SPECIES 

 LIVING SPECIES 



RARE 



EXT<NCT GPECIES 



A3UNDANT 



LIVING GZMERA, 



I. EOCENE 



LIVINQ FAMILIES 

 AND ORDERS 



SECONDARr PERIOD 



