The Classification of Geographic Forms hy Genesis. 27 



THE CLASSIFICATION OF GEOGRAPHIC FORMS BY 



GENESIS. 



By W. J. McGee. 



Scientific progress may be measured by advance in the classi- 

 fication of phenomena. The. primitive classification is based on 

 external appearances, and is a classification by analogies ; a higher 

 classification is based on internal as well as external characters, 

 and is a classification by homologies ; but the ultimate classifica- 

 tion expresses the relations of the phenomena classified to all 

 other known phenomena, and is commonly a classification by 

 genesis. 



The early geologic classification was based chiefly upon simple 

 facts of observation ; but with continued research it is found 

 that the processes by which the phenomena were produced may 

 be inferred, and, accordingly, that the phenomena may be grouped 

 as well by the agencies they represent as by their own character-, 

 i sties. Thus the empiric or formal laws of relation give place to 

 philosophic or physical laws indicating the casual relations of the 

 phenomena, and the final arrangement becomes genetic, or a 

 classification by processes rather than products. 



The phenomena of geography and geology are identical, save 

 that the latter sciencejncludes the larger series : since the days 

 of Lyell the geologist has seen in the existing conditions and 

 agencies of the earth a reflection and expression of the conditions 

 under which and the agencies by which its development has been 

 effected ; the far stretching vista of geologic history is illumi- 

 nated only by knowledge of the earth of to-day ; and the stages 

 in geologic development are best interpreted in terms of geogra- 

 phy. So a genetic classification of geologic phenomena (which 

 is rendered possible and intelligible through geographic research) 

 will apply equally to geography, whether observational or of the 

 more philosophic nature which Davis proposes to call Systematic 

 Geography, and which Powell has called Geomorphology. Such 

 a classification is here outlined. 



The various processes or movements with which the geologist 

 has to deal fall naturally into two principal and antagonistic cate- 

 gories and five subordinate categ^ories ; and each category, great 

 and small, comprises two classes of antagonistic processes or 

 movements. 



