ORGANIC DEPENDENCE AND DISEASE 27 



TABLE OF GEOLOGICAL DIVISIONS ADAPTED TO NOETH AMEEICA 



ERAS AGES PERIODS CHARACTER OP LIFE 



Psychozoic 



Eecent 



Else of intelligence and age of man. 



Cenozoie 



Quaternary 



Pleistocene 

 (Glacial) 



Successive glaciation, wide extinction 

 of life through cold, followed by quick 

 readjustments and rapid evolution. 



Pliocene The vertebrate stock approaches phys- 



Miocene ical culmination; obscure mammals 



Oligocene achieve the erect position. The earlier 



Eocene mammals are of simple type. 



Tertiary 



Mesozoic 



Cretaceous 



Upper 



Lower 



Diminutive and priraitive marsupial- 

 like mammals continue to the close of 

 this period and start upon a specific 

 upward progress. 



The great reptiles are becoming fewer 

 after having governed the earth in 

 infinite variety. 



Jurassic 



The reptiles at maximum development. 

 In the period of their earlier and more 

 plastic expressions birdlike reptiles de- 

 veloped and started the race of birds, 



Triassic 



While their origin-stock is represented 

 by the primitive dinosaur reptiles. Here 

 are the first traces of the mammal stock. 



Paleozoic 



Permian 

 Carboniferous 



Climax of Cryptogamous plants. Land 

 reptiles and Amphibians fully estab- 

 lished. Stalked Echinoderms (crinoids) 

 at their maximum. 



Devonian 



Culmination of lung and armored fishes 

 and primitive sharks. Beginning of 

 forests. 



Silurian 



Scorpionlike arachnids (Eurypterida) 

 at their maximum. 



Ordovician 



Cambrian 



Eeign of invertebrates of all stocks, 

 largely alfected by dependence and loss 

 of function except in Cephalopod mol- 

 lusks and Crustacea, but locomotive 

 independence was more generally re- 

 tained in the older faunas. 



Proterozoic 



and 



Archeozoic 



Worms, Eadiolaria, Calc-algae, Bacteria. 



