The Classification of Geographic Forms hy Genesis. 33 



the divides ; and, although these geologists have not dwelt upon 

 and perhaps have failed to perceive the relation, the same classi- 

 fication is as applicable to every feature of the local relief as to 

 the streams by which the relief was developed. 



In a general classification of the topographic forms developed 

 through gradation, it would be necessaiy to include the forms 

 resulting from deposition as well as degradation, and also to dis- 

 cuss the relation of base-level plains to antecedent and consequent 

 relief ; but in a brief resume it will suffice to consider only the 

 modifications produced by degradation upon a surface of deposi- 

 tion after its emergence from beneath water level as a regular or 

 irregular terrane ; and the influence of base-level upon the topo- 

 graphic forms developed upon such a surface may be neglected in 

 a qualitative discussion, though it is quite essential in quantitative 

 investigation. 



The hydrography developed upon terranes affected by displace- 

 ment both before and after emergence has already been satis- 

 factorily classified. Powell, years ago, denominated valleys estab- 

 lished pi-evious to displacement of the terrane by faulting or fold- 

 ing, antecedent valleys ; valleys having directions depending on 

 displacement, consequent valleys ; and valleys originally estab- 

 lished upon superior and subsequently transferred to inferior ter- 

 ranes, superimposed valleys ; and these valleys were separated 

 into orders determined by relation to strike and again into vai'ie- 

 ties determined by relation to subordinate attitude of the terranes 

 traversed. Gilbert adopted the same gei^eral classification, and 

 so extended as to include certain special genetic conditions. 

 Tietze, in the course of his investigation of the Sefidrud (or 

 Kizil Uzen) and other rivers in the Alburs mountains of Persia, 

 independently ascertained the characteristics of the class of water- 

 ways comprehended by Powell under the term antecedent ; 

 Medlicott and Blanford observed that many of the Himalayan 

 rivers are of like genesis ; and Riitimeyer, Peschel and others 

 have recognized the same genetic class of waterways ; but none of 

 these foreign geologists have discussed their taxonomic relations. 

 Lowl, who upon a priori grounds denies the possibility of ante- 

 cedent drainage, has recently developed an elaborate taxonomy of 

 valleys which he groups as (a) tectonic valleys, and (6) valleys of 

 erosion (Erosionsthaler). The first of these categories is separated 

 into two classes, viz : valleys of flexure and valleys of fracture, and 

 these in turn into several sub-classes determined by character of 

 the displacement and its relations to structure ; and the second, 

 3 



