I92I. No. II. THE STRANDFLAT AND ISOSTASY. II 



lower level, would wear away more or less the traces of the upper level, 

 and would produce a gradual transition from it towards the lower one. 

 But this is not the nature of the two levels. 



By marine denudation, working conjointly wnth subaërial denudation, 

 we get a simple explanation of the two levels of the strandfiat. The plane 

 of the lower one is cut backwards under the upper one, and both may exist 

 simultaneously, because the latter one will not disappear till it is entirelv 

 cut away by the lower level; and a more or less abrupt transition between 

 them may be found, unless it has been much modified by later erosion. 



An important reason why A. thinks that the Norwegian strandfiat has 

 not been formed by marine denudation, is that a plane thus formed could 

 not slope so very gently from its inner margin, at the foot of the moun- 

 tains, towards the outer skerries, as does the strandflat. Its inclination 

 must have become steeper, for else the weaves would not have got suf- 

 ficiently deep water to work in. Nevertheless he thinks that the innermost 

 parts of the very flat platforms on A'æroi, Rost, and probably also on 

 Træna, are formed by wave erosion. A. is obviously right in his view 

 that w'ave erosion alone cannot, as a rule, form wide planes sloping as 

 gently as these; but he has not considered the effect of shore erosion by 

 frost. Where this process, as described later, plays the leading rôle in 

 marine denudation, wide and nearly horizontal planes, like those of the 

 Norwegian strandflat, may certainly be formed along a much dissected 

 coast. 



On the other hand A. objects that, because in some places, c. g. in 

 the region of Rorvik, north of the Trondhjem region [1919, p. 197], the 

 low coastal border-land is not flat, there is no strandflat. For if this 

 "had been formed, wholly or mainly, through marine abrasion, the plain 

 would everywhere have the same main character," but "at Rørvik, and 

 at many other places, there occur, in complete contrast to this, all stages 

 from the most broken topography to the groups of small level islands." 



This is, however, just what might be expected to be a characteristic 

 feature of a strandflat formed by the joint action of subaërial denudation 

 and marine denudation, and also glacial erosion, along a much dissected 

 coast. Its degree of evenness will naturally depend on the degree of 

 maturity to which it has been developed. The less mature the more 

 ridges, hills, and stacks will surmount the general marine level. Where 

 the rocks are relatively resistant, or where initially relatively great masses 

 of rock surmounted sea-level, many islands and hills mav remain more or 

 less incompletely levelled, and their summits may vary much in height. 



On the whole, the surface of the strandflat may seem to be remarkably 

 level, considering that it has also been exposed to considerable glacial 

 erosion, perhaps during several periods, which has scoured the islands 

 and hills, rounding off their edges and sunnnits, and also considering 



