Smith.] 



Some Aspects of Erosion. 



177 



delta deposits, or submarine abrasion. Even if beveling were sub- 

 stituted entirely for peneplanation it would not follow (as Professor 

 Davis asserts *) that plains of marine abrasion would be discarded 

 as well. The question as raised by Professor Tarr is one of causes 

 rather than of results; and because one cause is discarded, it by no 

 means follows that similar results due to another cause are discarded 

 along with it. 



Finally (as already suggested, p. 156), in accounting for many 

 instances of the uniformity usually expressed by the term pene- 

 plain, it is quite possible that a combination of two or more of the 

 available explanations may be called for. An intelligent opinion 

 can be formed, in many cases, only after a study of the geology in 

 connection with the topography of the region. No broad general 

 rule can be laid down, but each field must be interpreted by itself. 



University of California, October, i8gg. 



*Loc. cit, p. 233. 



