I92I. No. II. THE STRAXDFLAT AND ISOSTASV. I39 



Il niav be asked whether these extensive horizontal plains have 

 actually been cut in solid rock. The many hundreds of islets and skerries, 

 scattered over their surface and rising above sea-level, prove, however, 

 that they must be rocky plateaus, although this does not make it impos- 

 sible that their surface may to some extent be levelled by loose material. 

 The sharply defined channels traversing them, with well markel edges 

 and the sharply marked edges on their outer seaward borders where they 

 are exposed to the full fury of the ocean, creating a violent surf, se?m, 

 however, to prove that the horizontal plane of these plateaus is actually 

 to a very considerable extent cut in solid rock. 



It is obvious that horizontal, rocky plateaus, with wide dimensions 

 such as these, cannot have been formed in postglacial time, nor can they be 

 cut by wave erosion. They must have been finally planed by shore erosion 

 by frost at some period or periods before the last glacial epoch. As they 

 have so much wider an extent than the plains of the emerged strandfiat 

 on the islands and the mainland they may possibly have needed a longer 

 time for their formation than the latter, although we have to consider 

 that the previous strandflat over these now submerged plateaus was 

 probably low, and that it was much dissected. 



In the region of Donna and Heroi Sahlstrom [1915' has studied the 

 emerged strandflat. and has by very accurate levelling constructed some in- 

 structive profiles across the northern flat part of Donna, across Southern 

 Heroi. and across Blomsoi (Fig. 113). The strandflat forms her^ quite 

 remarkably flat and extensive planes. 



On the northern part of Donna (see Fig. 114. II) the plane is 9 to 10 

 metres above sea-level, and in some places (Rølvag) 1 1 metres. There are 

 numerous small depressions and small valleys, but they are as a rule only 

 some few metres below the uniform level of the solid bare rocks projecting 

 in the surface of the ground, and are often not so large that in my opinion 

 a great many of them may not more or less have been formed originally 

 when this strandflat was planed by the frost in the shore and by the waves, 

 and have only been slightly modified later by subaërial denudation and 

 by glacial erosion. As mentioned before, there is a great resemblarce 

 between these planes and the level surface of the submerged plateaus in 

 the sea outside. 



Some few isolated hills rise above this plane to heights of 21 to 35 

 metres above sea-level, and near the east coast of the island to 42 and 50, 

 or a few even higher. The plane extends horizontally to the foot of these 

 hills and there is as a rule a quite sharp demarkation line, almost like 

 a shore-line, which, however, is often covered by shore gravel, and talus 

 débris. 



The region of the strandflat of the northern part of Donna is built 

 up of mica-schist, gneiss, and to some smaller extent of crvstalline 

 limestone. 



