The Classification of Geogra/phic Forms hy Genesis. 35 



hof en, and other continental, as well as different British and Indian 

 geologists, and Lesley in this country, indeed recognize this type 

 of drainage, but they do not correlate it with the montanic types; 

 and Lowl's designation, derived from the manner in which he con- 

 ceives it to be generated (" rtickschreitende Erosion"), does not 

 apply to either the completed drainage, or the coincident topog- 

 raphy. 



Although its subordinate phases are not yet discriminated on a 

 genetic basis, this type or order of drainage is sufficiently distinct 

 and important to be regarded as coordinate with the type repre- 

 sented by the entire group of categories recognized by Powell 

 and clearly defined by Gilbei't. Such hydrography (which either 

 in its natural condition or superimposed characterizes many plains, 

 some plateaus, and the sides of large valleys of whatever genesis) 

 may be termed autogenoics ; while the drainage systems imposed 

 by conditions resulting from displacement (which charactei'ize 

 most mountainous regions) may be termed tectonic. Gilbert's 

 classification of drainage may then bo so extended as to include 

 topography as well as hydrography, and so amplified as to include 

 the additional type. 



Drainage systems and the resulting systems of topography (all 

 of which belong to the degradational class of forms) are accord- 

 ingly.— 



Type 1, Autogenous. - 

 Type 2, Tectonic— 



Order A, Consequent, upon 



Class a, Displacement before emergence, and 

 Class 5, Sudden displacement after emergence; 

 Order B, Antecedent ; and 

 Order C, Superimposed, through 



Class a, Sedimentation (when the superimposed drain- 

 age may be autogenous). 

 Class 6, Alluviation or subaerial deposition, and 

 Class c, Planation (in which two cases the superim- 

 posed drainage may simulate the autogenous 

 type). 



In brief, the entire domain of geologic science is traversed and 

 defined by a genetic classification of the phenomena with which 

 the geologist has to deal ; and the same classification is equally 

 applicable to geographic forms, as the accompanying table illus- 

 trates : 



