188 W. M. DAVIS NOMENCLATURE OF SURFACE FORMS 



graphical problems of surface forms as determined by the action of ero- 

 sional processes on faulted structures. The terminology here suggested 

 for surface forms of this class is closely related to a systematic method 

 of physiographic description which may be called the method of "struc- 

 ture, process, and stage," in that it recognizes, first, the underground 

 structure — often called the geological structure— of the mass which ex- 

 hibits physiographic forms in its upper surface : second, the process or 

 processes which have worked on the structural mass so as to modify 

 its initial surface forms; and. third, the stage reached by the action of 

 process on structure in producing the actual forms under consideration, 

 in view of the whole series of stages from the initiation of erosional work 

 by the uplift of the structural mass to the completion of erosional work 

 by the reduction of the mass to a featureless plain. Belief, or local 

 inequality of altitude, and texture, or spacing of stream-lines, are also 

 given explicit attention in the fully developed application of this sys- 

 tematic scheme, but they will not be closely considered here. As the 

 proposed terminology for surface forms on faulted structures is thus 

 related to a comprehensive plan of treatment for all sorts of forms on 

 all sorts of structures, the terms can not be well understood from defini- 

 tions alone. Their meaning can be better gathered from the following 

 statement of the manner in which they are used. 



The Cycle of Erosiox 



It appears from the foregoing that an important feature of the scheme 

 of "structure, process, and stage" is the recognition of the systematic 

 sequence of surface forms that must be developed during the progre— 

 erosional work on structural masses. Various essential terms in the 

 scheme are related to the sequence in which surface forms are produced, 

 and the chief of these will now be concisely stated. The time required 

 for the completion of the whole series of erosional changes, between the 

 initiating uplift of a land-mass and its ultimate reduction to a feature- 

 less lowland or to a submarine platform, is called by American physiogra- 

 phers a cycle of erosion : and all the members of the systematic sequence 

 of forms produced during the normal progress of a cycle of erosion may 

 therefore be called sequential forms — the three terms, initial, sequential, 

 and ultimate, so appropriately related to one another in this scheme, 

 having been first introduced by Dr. F. P. Gulliver in his study of '"Shore- 

 line Topography" ( '99 | . 



It has become to be habitual with many physiographers to speak of 

 the early, intermediate, and late members of such a sequence as young, 



