30 National Geographic Magazine. 



There is a final category which is in part allied to alteration 

 but is in part unique, viz : the chemic, mechanical, and dynamic 

 action of organic life. Ever since the terrestrial crust become so 

 stable as to retain a definite record of the stages of world- 

 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 their pro- 

 cesses of growth and decay, as do the lower plants and animals 

 of the present ; later, certain organisms contributed largely of 

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

 the highest organisms, with man at their head, have by dynamic 

 action interfered directly with gradation, alteration, and wind- 

 action, and thus, perhaps, indirectly with the more deep-seated 

 processes of world growth. The vital forces are too varied in 

 operation to be conveniently grouped and named. 



These categories comprise the various processes contemplated 

 by the geologist, and collectively afford an adequate basis for a 

 genetic classification of geologic science. Their relations are 

 shown in the accompanying table : 



Classification of Geologic Processes. 

 r-^ ^ fl. — Def or- J Antecedent<Epeirogenic ^ 5 ^l^vation 





mation. ^ Consequent>Orogenic. ^ ^Depression. 



3. — Gradation. j Deposition. 



I Degradation. 



f 1. — Vulcanism. j Extravasation. 



(Antithesis of Extra v.) 



2. — Alteration | Lithif action. 



} Decomposition. 



3. — Glaciation. | Glacial construction. 



] Glacial destruction. 



4. — Wind action. \ Wind construction. 



] Wind destruction. 



5. — Vital action. ( Various constructive and 



] destructive processes. 



On applying this classification to geographic forms, the various 

 phenomena immediately fall into the same arrangement. The 

 continents, great islands, mountain systems, and non-volcanic 

 ranges and peaks generally, the oceans, seas, and some bays, gulfs 

 and lakes, evidently represent the diastatic category of move- 

 ments. These greater geographic features have long been named 



