194 



The Field of Geology — McGee. 



growth, life has existed, and by its traces has furnished the ac- 

 cepted geologic chronology; at first the organisms were simple and 

 lowly and affected the rocks chemically through the processes of 

 growth and decay as do the lower plants and animals of the pres- 

 ent; later, certain organisms came also to contribute largely of 

 their own bodily substance to the growing strata; and still later 

 the highest organisms, with man at their head, have come to inter- 

 fere with gradation, alteration and eolation by dynamic action, and 

 thus directly or indirectly to modify the various inter-related geo- 

 logic processes — indeed it is probnble that in populous plains, at 

 least, the several natural processes combined are less f)otent factors 

 in geologic development than human action alone. The vital 

 forces are too varied in action to be conveniently grouped and 

 comprehensively named. 



This simple classification of processes appears to traverse the 

 entire domain of geologic science, whether empiric or philosophic, 

 and sets forth the various parts in true relation. It is summarized 

 in the accompanying table. 



Classification of Geologic Processes. 



Principal J 



f 1. Deformation 



ion, \ ^ «^''"°°- 

 ' ( Depression. 



Categories. 



!^ 2. Gradation, 



1. Extravasation 



2. Alteration, 



Deposition. 

 Deofradation. 



Subordinate 

 Categories. 



^ 3. Glaciation, 



4. Eolation, 



5. Vital action. 



Efflux. 

 Collapse. 



Lith if action. 

 Delithif action. 



Glacial construction. 

 Glacial destruction. 



Eoiic construction. 

 Eolic destruction. 



Various constructive and 

 destructive processes. 



It is interesting to note in passing that the first subordinate 

 category is intimately connected with the first principal category 

 of movements, and that both tend to produce departures from the 



