I92I 



. No. II- THE STRAXDFLAT AND ISOSTASV 



the same depth. The side slopes are g-eneraU}' vei-\ ^tccp and there are 

 often channels and hollows with considerable depths just outside or on 

 the sides of these plateaus. 



It mav seem difficult to find a satisfactory explanation of this 

 difference between the two kinds of plateaus. One mig^ht have expected 

 that the plateaus of less resistant rocks should have been more attacked 

 bv recent erosion, and more denuded, and consequently lower, than the 

 granite plateaus. 



The only explanation I can find, is that the plateaus of rocks with 

 little power of resistance have formerly had a greater extent, and have 

 formed fairly compact land masses rising above the sea. After the land 

 had been more or less worn down, the outer part of these plateaus have 

 been much cut back, also during the last glacial period, by the glaciers 

 excavating the deep channels and hollows outside them where the weak 

 rocks offered especially favourable conditions for the glacial erosion. 

 This is the reason why there are often such deep channels and hollows 

 with very steep side slopes outside these plateaus. 



It is probable that the erosion of glaciers in rocks with comparatively 

 little power of resistance to frost erosion, produces a very different sculp- 

 turing above and below the water surface. Above the sea the mountain 

 slopes on the sides of the glaciers are much attacked In- the frost erosion. 

 and the result is comparatively broad valleys with sloping sides. Below 

 the sea this is entirely different, the rocks are protected by the sea against 

 the frost erosion, and there will onlv be erosion on the under side of the 

 moving glaciers. They will therefore cut narrower channels with steeper 

 side slopes, and sharply defined edges bounding the flat plateaus which 

 will not in interglacial time be attacked and rounded off by frost erosion 

 or subaëria! denudation against which they are protected by the sea. 

 The still remaining middle parts of the plateaus were truncated by 

 the shore erosion comparatively recently. They are, therefore, very level, 

 standing near present sea-level, as there has been but little time for the 

 wave erosion or for glacial erosion to wear them down to greater depths. 

 It might be asked where are the older plateaus cut in this kind of 

 rock? and why do we not find them at lower levels? The answer may be 

 that where the older plateaus were cut in weaker rocks, thev have b3en 

 more or less cut back by the glaciers during the subsequent glacial periods, 

 and they no longer exist as parts of the submerged strandfiats. 



The map Fig. 113 also shows that the outer edges of the plateaus of 

 mica-schist and limestone, e. g. at Flovær and Skjærvær, are cut back 

 more than the edges of the granite plateaus at Lyngvær, Slaggrunnen. and 

 Floholman to the north, and at Sjola and Steinan to the south. The 

 plateaus at Ertenbraken and Storbraken are also cut back with deep 

 channels and hollows round tiiem. 



