192 W. M. DAVIS NOMENCLATURE OF SURFACE FORMS 



strong faulting of a land mass of any structure that has already reached 

 any stage of erosional development in a preceding cycle. Be it noted, 

 however, that the "strong faulting" is not to be understood as accom- 

 plished all at once, but by a succession of small faults, each of which 

 alone would be, as already indicated, merely an episode, although all. 

 taken together suffice to interrupt the cycle previously current and to 

 introduce the new one. We then follow the sequential changes as far 

 forward through the new cycle and through later cycles as is profitable, 

 and give appropriate names to the more important forms that are asso- 

 ciated with the fault at successive stages during successive cycles in the 

 work of erosion on it. 



As long as our discussion is presented only in verbal form, its general 

 values, indicated in such phrases as "a land mass of any structure in any 

 stage of development" may be preserved : as soon as a diagram is added 

 to give graphic illustration of verbal meaning the discussion is in danger 

 of losing much of its generality, for a single diagram can show a land 

 form of only one structure and usually of only one stage. Nevertheless, 

 such are the advantages of graphic illustration that diagrams can not be 

 dispensed with ; their dangers may perhaps be lessened by using series of 

 composite diagrams, as in figures 1 and 2, the two series having different 

 structures and each series showing a number of successive tages. Fig- 

 ure 3 shows only a single mature stage of a mountainous district of 

 massive structure crossed by recent faults. The variety of faulted struc- 

 tures is evidently endless, yet a comparatively simple scheme of treatment 

 may be adapted to all of them. Step-faults may be best treated by giving 

 separate account of each of their members. Renewed faults may involve 

 several successive interruptions of cycles of erosion instead of a single 

 interruption. Hence all that need be done here is to develop a scheme of 

 treatment for a few simple examples ; the scheme may afterward be modi 7 

 tied as needed for complex examples. 



Initial and young Forms on faulted Structures 



Imagine, then, a surface of any kind- — for example, a young lava plain, 

 A, figure 1, or a district of subdued or old crystalline hills, A, figure 2, 

 or a mature, mountainous mass of deformed strata, figure 3. Let the 

 surface be traversed by a fault of moderate displacement, producing a 

 low fault scar]). B. For simplicity of introductory discussion, let the 

 lower part of the faulted mass remain for the present in its former atti- 

 tude with respect to baselevel, so that erosion is revived only in the up- 

 lifted part. 



