STAGES OF THE EARTH'S HISTORY 



435 



truth cannot be at once demonstrated, lies mainly in its working 

 qualities. 



(7) The gradational stage. .To complete the survey of stages, 

 it is necessary to note that after the growth of the earth had ceased 

 and volcanic action had passed its climax, the surface was no longer 

 subject to continual burial, but was exposed, age after age, to the 

 action of air and water. The material removed by these agents 

 from the higher parts was deposited in the basins. Throughout 

 all this remaining period, the dominant geologic processes were 

 therefore gradational. Vulcanism and diastrophism continued 

 to be important, but not dominant. This stage embraces the 

 Proterozoic and later eras. 



Synoptical View of the Earth's History 



The stages of the earth's history fall into two great groups, with 

 a transition period between. The first group includes the stages of 

 growth and the last the stages of maturity. In tabular form, and 

 numbered in chronologic order, these stages appear as follows: 



III. 



II. 



maturity) 

 The Extrusive f 



H 



The Paleozoic era 

 The Proterozoic era 



The Archeozoic era 



The better 

 known eras 



I. 



