392 DAVIS — PLAINS OF MARINE AND SUBAERlAL DENUDATION. 



In his compendious volumes on the " Morphologic der Erdoberfliichc " 

 (1894), he considers plains of marine and of subaerial denudation, l^oth 

 as to process of origin and as to derivative forms, after elevation and dis- 

 section, but criteria for their discrimination are not discussed * 



De Lapparent, president of the French Geographical Societ}'', has 

 advocated subaerial erosion as the means of denuding the Ardennes and 

 the Central plateau of France, t and later says : 



" La notion des penc'jilaines est extrenienicnt fi'conde, et ce n'cst ])as nn d(' sos 

 moindres nierites d'avoir porte Ic coup de grace a la tlieorie des plaines de denuda- 

 tion marine, si fort en honneur de I'autre cote du detroit." J 



Comparison of the two Schools. 



It is notewortli y tlint, with few exceptions, the more recent writers liere 

 quoted do not discuss both processes by which smoothly abraded i)lains, 

 whether l)uricd or bare, ma}' be produced, but directly announce their 

 conclusion as to the origin — by marine or by subaerial agencies — of tlie 

 surface under consideration. This, of course, itn])lies that they regard 

 the (picstion as settled, just as for somi^ time l)ack it has been tlic l)al)it 

 of geologists on finding marine sliells in stratified rocks to conclude, witli- 

 out reviving the discussions of earlier centuries, that the strata are of 

 marine origin, and that their present i)()sition indicates a change in the 

 relative attitude of the land and sea. But in this latter exnmple all 

 geologists are today agreed, while in the problem of the origin of plains 

 of denudation each writer follows only the conclusion of his own school, 

 not the conviction of the world. It is chiefljj to arouHC attention to tfils aspect 

 of the problem that the present review is undertaken. 



It is furtlier noteworthy that, with few exceptions, the autliors who 

 discuss the matter at all do not attempt to discriminate between the two 

 possible classes of denuded surfaces by searching for features peculiar 

 to one or the other, but content themselves with a priori argument as to 

 the possibility of producing plains by marine or subaerial agencies. 



There is, however, a certain difference of attitude in the two schools 

 regarding the doctrine of the other. The English school hardly considers 

 at all the ability of subaerial agencies to produce smooth plains of denu- 

 dation ; their discussion of the question turned really on the possible 

 origin of valleys by sul)aerial agencies. The American school does not, 

 as far as I have read, deny tlie ability. of marine agencies, but attril)utes 

 greater ability, especiall}'' far in continental interiors, to subaerial agencies ; 

 their discussion of the question postulates the subaerial origin of ordinary 



* Vol. ii, pp. 145, 181, 489. 



t L'age des formes topographiquep, Rev. des quest, scicnt., Oct., 1804. 



J La g6omorphog6nie, ibid., April, 1895. 



