144 



I"KIt)TJOr NANSF.N. M.-N. Kl. 



(j^-raiiitc), riMiiaiii. iii<licat in- llic initial lici.c^Iil oi' tlic- laiul, and haviiij^ oii 

 their lop often llie old surface, or l'alæic lanrl surface, extendinj^^ almost 

 unaltered lo the ed^^cs of the j)recij)itous mountain sifles, which is a con- 

 vincing,^ proof that, durini;- ihe time when ihe slrandflal was foriïied, the 

 effect (jf the suhaerial denudation was of but little importance as com- 

 pared with that of the sliore-erosion, where the latter was as effective as 

 in this rej^J'ion. 



Other convincin,«;- evidence of the efficacy of the shore-erosion are 

 the many big caves on the islands of Træna. As the floors of these caves 

 are at levels between 29 and 56, and some even at about 70 metres, above 

 the sea [cf. Oxaal, 1915, P- 72], and conse(|uently above the level of the 

 strandfiat, they must have been formed during- comparatively short periods 

 when the land was temporarily submerged to these levels. 



The fact that caves such as these formed in granite or gneiss, only 

 occur near the coast and especially on the most exposed parts of it. indi- 

 cates that they have been formed by shore erosion. 



In mv opinion, the chief agency which lias helped to form them i- 

 the frost. This is already indicated by the fact that such caves are 

 especially numerous in the northern parts of the Norwegian coast, and 

 the great majoritv of them do not occur near present sea-level, but at 

 levels to which the land was submerged during the glacial periods, and 

 when there were cold climates. In more arctic latitudes, e. g. on Bear 

 Island and Spitsbergen the caves occur mostly at the present sea-level. 

 As has been pointed out by Rekstad and Oxaal and previous writers, 

 the caves are formed along fracture lines, or line,s of weakness, in the 

 rock. Here the frost had easy work by breaking loose blocks along the 

 many fissures of the rock. Where the water in the rock was permanently 

 frozen, its temperature would be near melting point where the rock sur- 

 face was near the sea water, and frequent daily changes in temperature 

 above and below freezing point would be caused by the temporary con- 

 tacts with the warmer sea water, especially due to the tide, but also 

 occasionally to storms. 



The stones thus loosened by the active frost will tumble down from 

 the roof and the walls of the caves. They will also easily be broken away 

 by the waves, especially during storms, and where the caves have the 

 required shape for it, the alternate compression and expansion of the air 

 m the caves by the waves, may have a considerable effect in breaking 

 loose the stones, as was pointed out by Rekstad [1912, pp. 59 f"-. cf. also 

 Oxaal, 1915. pp. 74 f-1- The stones thus broken loose, will accumulate on 

 the floor of the caves, where they will be exposed to a vigorous dis- 

 integration by frost when the floor is alternately submerged and left dry 

 by the tide. Especially during winter, ice is also formed on the floor, and 

 when shifted and broken loose in summer, it may help to carry away 

 material. That the wave action generally is of little direct importance for 



