I92I. No. II. THE STRANDFLAT AND ISOSTASY. 24I 



It thus seems probable that thie continual deposition of sediment on 

 the sea-floor has in the course of time actually caused an appreciable rise 

 of the g-eneral sea-level. At the same time there has been a gradual sub- 

 sidence of the sea-floor and an upheaval of the continents. 



If we imagine that, to begin with, the outer border of the continental 

 surface was low and to some extent submerged below sea-level, then the 

 emerged parts of this continental border would be exposed to marine 

 abrasion as well as to subaerial denudation. By the joint action of these 

 two agencies the emerged portions of the land surface would after a long 

 time be planed down towards sea-level, while the depressions of the sub- 

 merged surface would be more or less filled up with the waste from these 

 emerged parts and from the continental surface inland. At the same time 

 there would be a continual deposition of sediment on the continental slope, 

 outside tlie submerged outer border of the flat continental surface. 



In the course of time the result of these processes would be that the 

 sea-floor of the continental slope would be gradually depressed under the 

 heavy weight of the increasing layers of sediment. On the submerged 

 continental border there has been a depositic i of waste from the inner 

 part of the continent in addition to the Avaste formed by the denudation 

 of the emerged portions of the coast. This border will consequently also 

 be pressed down to some extent. The emerged continental coast land 

 inside this submerged border, however, has been denuded by subaerial 

 erosion and A\ill be tipheaved. At the same time the general sea-level will 

 be somewhat raised by the general deposition of sediment on the Ocean 

 floor, and the submerged continental border will be still more sub- 

 merged. 



As the coasts would be continually exposed to the joint action of 

 subaerial denudation and marine abrasion they would gradually be cut 

 back; but this process would be extremely slow, as, owing to the general 

 subaerial denudation of the continental surface, the denudation of the 

 coastal land would be largely compensated for by its isostatic upheaval, 

 and it would therefore be chiefly the marine abrasion which would cut 

 T)ack the coast, as this denudation is limited to the shore and would 

 therefore create no appreciable upheaval of the land. 



Although weighty objections may certainly be raised against many 

 details of this theory, still I think it possible that on the whole it may 

 give a fairly feasible explanation of the formation of the continental 

 shelves. 



It would be easy to understand that along coasts where there was 

 no initial submerged border of the continental surface, the formation of 

 a continental shelf will be a difficult and extremely slow process. We 

 therefore find that the continental shelf is often very narrow outside such 

 high coasts, while it is, as a rule, broad outside coasts where the continental 

 surface is low and slopes gently towards the sea. 



Vid.-Selsk. Skrifter. I. M.-N. Kl. 1921. No. 11. 16 



