EUROPE BEFORE ARRIVAL OF MAN 



adoption of the Missouri Compromise. We 

 may know that it is so, but in order to make it 

 seem so, most people will have to stop and 

 think. 



The case is somewhat similar when we try to 

 realize the relative duration of the successive 

 geological epochs in the history of the earth's 

 crust. We are naturally inclined to overrate the 

 relative duration of the later epochs. Familiar 

 as we are with the established classification of 

 periods as Primary, Secondary, and Tertiary, 

 we fall naturally into a habit of regarding these 

 three great groups of epochs as substantially 

 equal in value, so that the beginning of the 

 Tertiary period is apt to seem one third of the 

 way back toward the first beginnings of fossil- 

 bearing strata. Probably in our every-day think- 

 ing the Tertiary period occupies more than a 

 third of the space that is occupied by the whole 

 recorded life history of the earth, mainly for 

 the reason that it is so much more completely 

 filled for us with familiar and well-ascertained 

 facts. This may be partly because organic life 

 has really been more complex and multiform 

 since the beginning of the Tertiary period than 

 it was in earlier ages ; but it is also, no doubt, 

 because our sources of information are far more 

 abundant. On the whole, the geologic record 

 of the Tertiary period is much more completely 

 preserved than that of the two earlier periods ; 

 3 



