,'}()() OTTILCHER [CHA7'. 1 :{ 



glaciation, l)ecause of the oiitfiow of magma in the subcnistal zone ; and 

 conversely, after the mehing of the ice, the i)eri])heral belt must have sunk to 

 some extent when the central tract rose (Daly, 19'H). Thus, isostatic movements 

 contrary to those occurring in glaciated areas may account for block-faulting or 

 rifting outside the main hinge line separating the glaciated belt from the 

 ]ieripheral area. 



As to the origin of the shelf itself in Norway, in the diastrophic interpretation 

 it "may be regarded as a paleic surface formed i)rimarily during the Tertiary, 

 and probably subject to block-faulting and to denudation by marine and sub- 

 aerial agencies during periods of changing relative sea-levels" (H, Holtedahl, 

 1955, p. 197). In other words, it was a downfaulted part of the planation 

 surface which bevelled the Scandinavian higlilands with some further modifica- 

 tions. The same explanation may be suggested for other glaciated lands, in so 

 far as a subaerial planation is likely to have affected them before they were 

 uplifted. There has been much controversy about the origin of the Scandinavian 

 shelf and the strandjiat which occurs just below or above sea-level in the 

 Norwegian coastal area. Other strandflats have been reported from Bear 

 Island, Spitzbergen, Iceland and Greenland. (A review^ of the opinions con- 

 cerning the possible origins may be found, with references, in Guilcher, 1958, 

 ]). 160.) As O. and H. Holtedahl suggested, the strandflat may be either a large 

 downfaulted block or a coastal marine surface, partly developed by ice-foot 

 corrosion, as Nansen believed. It may, on the other hand, be the result of the 

 recession of glacial corries, as Dahl proposed, or an old subaerial peneplain 

 (Ahlmann) or Rumpftreppe (Evers, 1941), partly reworked by wave action. 

 Many authors admit a compound origin, with one prevailing factor. In the 

 writer's opinion, faulting is likely to have played a major part; H. Holtedahl 

 (1955, p. 49) has given strong evidence for an extreme slow^ness of wave abrasion 

 along the coast of Norw ay ; at greater depths in the same region, the sediments 

 are poorly sorted and point to a glacial marine, not true marine, origin (see 

 Chapter 24 in this volume) ; in East Antarctica, the shelf seems not to have 

 been much smoothed by ice erosion, except for some rare areas. 



The considerable depth of the shelf in many glaciated areas has been sup- 

 posed to be due to overloading by ice-caps and incomplete postglacial isostatic 

 adjustment. This implies that the whole shelf has been covered by non-floating 

 ice as far as the outer edge, which is by no means sure, and even improbable in 

 a number of regions. 



5. 



Conclusion 



So far as the present state of knowledge allows a conclusion, the continental 

 margins appear to have a mainly diastrophic or constructional origin. Marine 

 erosion in shallow^ and coastal w^aters, including a luimber of processes of which 

 wave abrasion is probably less important, is responsible for some of the features, 

 but its action has been of limited extent. Turbidity currents, slumping and 

 sliding, which are discussed in Chapters 27 and 28 in this volume, must be most 



