214 W, M. DAVIS- — NOMENCLATURE OF SURFACE FORMS 



One might easily deduce, from what is already understood of the action 

 of sea waves on coasts of different kinds, a series of ideal types dependent 

 on faulted coastal structures — for example, the development of fault- 

 line chasms by the attack of; the sea on the weak breccia of a sheared 

 fault ; or the more rapid advance of the marine cycle on a body of weak 

 rocks alongside of its less rapid advance on a neighboring body of hard 

 rocks, the two rock masses having been brought together by a fault, re- 

 duced to subdued forms, and then submitted to marine action by depres- 

 sion. Similarly, a valley glacier, while actively over-deepening its trough, 

 might develop a more, or less abrupt step in the trough floor on passing 

 across a fault from a resistant to a weak rock body; or a basin, on pass- 

 ing from a weak to a resistant rock body; likewise, the trough walls 

 might be well smoothed or matured in less resistant rocks, while they 

 still retained ragged or youthful features in more resistant rocks, as ap- 

 pears to me to be the case in certain glaciated troughs of the Snowdon 

 district in Wales, although the juxtaposition of the two rock masses was 

 not, as far as I know, in that case brought about by faulting. The fuller 

 discussion of these and many other examples may wait till it is wanted. 

 In all these cases the object in view and the principles to be observed 

 in reaching it remain the same. The object is the explanatory 'descrip- 

 tion of the visible landscape as directly as possible, with no more of past 

 geological history than is helpful in attaining this object. The principles 

 already illustrated regarding the description of the pre-faulting forms, 

 of the direct effects of faulting, and of the post-faulting forms may be 

 expanded so as to include the description of forms developed under the 

 action of different processes, as has already been implied in the mention 

 of coastal forms in earlier paragraphs. For example, when one process is 

 replaced by another, the description of the resulting forms should in- 

 clude the forms reached under the first process at the time of change, 

 then the change of process, and lastly the forms developed by the new- 

 process as modifications of the previous forms. In brief: here, as in all 

 other cases, let the physiographer answer the question, "What does it 

 look like?" in terms of the visible products of the work of processes on 

 structures, and his work will be accomplished. 



Definitions of Terms used in describing Forms ox faulted 



Structures 



It may now be better understood than at the beginning of this paper 

 why the nomenclature of surface forms produced by the erosion of faulted 

 structures — that is, the physiographic nomenclature of faults — was not 

 introduced by definitions of a geometrical kind. Such definitions might 



