I 92 I. No. II. THE STRANDFLAT AND ISOSTASY. I 45 



the disintegration of the stones is proxed hy the tact that as a rule little 

 rolled material, pebhles or boulders, are found in the caves. 



The often cirque-like valleys with precipitous sides on the Træna 

 Islands have also, in mv opinion, been formed by the shore-erosion to a 

 verv great extent. Oxaal [1915- I'- 79] thinks they have been formed by 

 the wave erosion, but I consider it j^robablc that in their formation also 

 the frost has been the chief causal agent, although it has been effectively 

 assisted by the wave action. It may be doubtful whether it is justifiable 

 to make such an absolute difference between these kind of formations 

 and the ordinary cirf|ue valleys. I think the first commencement of these 

 valleys may often have been small regular cir(|ues eroded by small local 

 glaciers or accumulations of snow and ice, in the manner I have discussed 

 before (cf. p. 2' , and Fig. 8). This erosion has then been continued by 

 the frost erosion in the shore, of the kind described in C"hap.\' (pp. 28 ff.), 

 which is to some extent of the same nature as the erosion of the small 

 cirque g;laciers. The shore-erosion l\v frost has at times been vigorously 

 aided bv the violent wave actioit, breaking and carrying away all loosened 

 material. In this manner the combined erosion of frost and waves ad- 

 vances comparativelv rapidlv along- the lines of fracture and weakness of 

 the rock, and forms small cir(|ue vallevs which may develop into narrow 

 passes breaking through the mountain ridges. 



Considering the vigorous marine denudation, to which the Træna 

 Plateau has been exposed, it was to be expected that it would have a well- 

 developed strandfiat, although it is to a great extent built up of compara- 

 ti\'ely resistant rocks. 



It would have been of much interest to know exactlv the height of 

 the emerged strandfiat and especially its upper limit in this region, as 

 we might expect to find it fairlv sharply defined at the foot of the steep 

 mountain sides. Oxaal mentions this strandfiat, but unfortunately he does 

 not seem to have actually measured its heights, and neither his description 

 nor his illustrations give any clear indication of the actual altitude of its 

 level i^lane or of its upper limit at the foot of the mountains. 



According to the maps ("Cjradavdelingskarter", in scale 1 : 1 00000) 

 marked "Trænen" and "Luroy", the many islands are in general less than 

 30 metres above sea-level, and only on some few of them does the low 

 lanrl rise to heights of between 40 and 45 metres. The probabilitv seems 

 to me to be that on the many low islands there is, to a great extent, 

 a low le\el similar to that measured by Sahlstrom on 1 )onna and Heroi. 

 Whether there is also a somewhat higher le\el approaching 30 or 40 

 metres is doubtful, but may be possible. 



The method employed by Oxaal, consisting in measuring with a 

 planimeter the areas between the contours for each thirty metres of height 

 above the sea, and for each ten metres of depth l)elo\v sea-level, and then 

 drawing a profile of the heights and depths of the plateau accordingly 



Vid.-Selsk. Skrifter. 1. -M.-N. Kl. 1921. No. 11. 10 



