20 GEOLOGY. 



The purpose of this general survey is to bring the salient features 

 of the earth's structure into view preparatory to entering in more detail 

 into the study of particular processes and special formations and to 

 lay a foundation for the fuller apprehension of the successive stages 

 of the history of the earth, which constitutes the chief purpose of geo- 

 logical study. It is now advisable to turn to the detailed consider- 

 ation of individual processes and specific structures. The complexity 

 of the actions involved in the history of the earth is so great that such 

 separate consideration at the outset is helpful. 



