1 92 1. No. II. THE STRANDFLAT AND ISOSTASY. 53 



An essential condition for the formation of the present strandfiat of 

 Norway did, however, not exist before the coast had been eroded and dis- 

 sected by the glaciers of the Great Ice Age. The preglacial fluvial valleys 

 were then much deepened, the coast was dissected by numerous deep fjords 

 and channels, and was split up into thousands of peninsulas and islands, 

 the length of the shore-line, /. c. the line of attack of the shore erosion, 

 was enormously increased. The waste on the land was swept away, and 

 bare rock-surfaces were exposed to the attack of the erosion, especially 

 the disintegration by frost. 



During interglacial times there may have been cold periods favouring 

 erosion by frost, at least along some parts of the Norwegian coast. But 

 especially the climatic conditions preceding and accompanying each glacial 

 period, greatly increased the subaërial denudation as well as the shore 

 erosion, in all regions not covered by the inland ice, i. c. especially the 

 outer coastal border along western and north-western Norway. During 

 these periods, as long as the level of the shore-line remained fairly stable, 

 before the land was too much submerged by the weight of the inland ice, 

 the strandfiat was chiefly developed, along the much dissected coast, by 

 the joint action of subaërial denudation, particularlv by frost, and local 

 glacial erosion on the peninsulas and islands outside the inland ice. and 

 finally by the shore erosion by frost and wave action. 



The two first mentioned processes were of main importance for the 

 denudation of the land towards sea-level; because they attacked the whole 

 land-surface, while the shore erosion gave the thus denuded uneven islands 

 and peninsulas their nearly horizontal plane. By the repeated advances of 

 the margin of the inland ice and its glaciers all waste was swept away 

 seawards from the land, and bare rock-surfaces were exposed to fresh 

 attacks of the erosion when the glaciers retreated. 



But as the shore-line was not quite stable, at least not during some 

 part of the time, when the final planes of the strandfiat were developed — 

 because, for instance, the sea-level was gradually lowered by the accu- 

 mulation of water in the ice-caps on land — the strandfiat was not finally 

 planed at a perfectly fixed level of the shore-line. Besides this, it is also 

 probable that when the land had again attained its level of isostatic equi- 

 librium, after each glacial period, the shore-line may have stood at a level 

 somewhat lower than that of the preceding interglacial time, owing to the 

 removal of a great deal of rock material anrl waste by the eros'on during 

 each glacial period, as w^ill be mentioned later. 



It is not, therefore, to be expected that the strandfiat as we now see it, 

 should form one definite anrl sharply marked plane. The level of its 

 surface may vary somewhat according to circumstances. 



Then it has also to be considered that during each glacial period the 

 strandfiat has been largely exposed to a vigorous glacial erosion which 

 may have modified its surface more or less, and made it more uneven. 



