190 W. M. DAVIS NOMENCLATURE OF SURFACE FORMS 



lifts, depressions, warpings, foldings, and deformations of any kind, we 

 are further concerned, because one kind of deformation embraces faults, 

 which involve differential movements of the two parts of a severed mass. 

 The development of a systematic terminology, consistent with the rest 

 of the terminology of the method of "structure, process, and stage," for 

 forms developed on faulted structures is the object of this paper. 



Relation of Faults to the Cycle of Erosion 



It is manifest from what is known -of many well studied examples of 

 faulted structures that a fault may take place in any direction and with 

 any displacement in a structural mass of any kind, at any stage in its 

 physiographic development, under the action of any kind or kinds of ero- 

 sional processes on its surface. It is also clear that, just as the fault may 

 have any relation to the underground structures that it traverses, so its 

 surface expression in a fault scarp may traverse indifferently all other 

 kinds of surface forms. Further, it follows that on account of the new 

 positions given to the two parts of the faulted mass with respect to base- 

 level, the surface action of the erosional processes must be more or less 

 changed as a consequence of faulting. The cycle of erosion previously cur- 

 rent should, therefore, in accordance with the scheme above stated, be re- 

 garded as "interrupted" and the further work of erosion be treated as 

 belonging to a new cycle "introduced" by the faulting; but, unless the 

 displacement of the fault be large, so strict an application of the scheme 

 of the cycle is not necessary; small disturbances may be treated as mere 

 episodes of a single cycle. Nevertheless, if a long succession of small 

 faults occur, the sum of their movements must suffice to interrupt the 

 preceding cycle and to introduce a new one, and the work that the ero- 

 sional processes were previously performing will thus in time come to be 

 seriously modified and an altogether new series of sculptured forms will 

 result therefrom. 



In view of the object of that section of modern physiographic study 

 which is concerned with the description of land forms, it is evident that 

 the terminology of surface forms developed on faulted structures must 

 have especial reference to existing surface features that are actuallv 

 visible. This is hardly more than a truism, yet it deserves conscious 

 recognition and emphasis, because it often happens that in the attempt 

 to give explanatory description to land forms the complications of the 

 past processes involved in the explanation distract the attention of the 

 reader from their visible product in the features of the present land- 

 scape and direct it to the past action of inferred processes on invisible 



