550 



NATURE 



[October 6, 1904 



been no oscillation of sea level, but that the channels 

 may have been excavated by glaciers to their present 

 position below the sea surface"; and, although the 

 author does not regard this possibility as of much 

 weight, we may recall attention to the interesting 

 suggestion (quoted in Nature, July 7, p. 218) made 

 by Mr. G. K. Gilbert, from his observations on 

 Alaska, that glaciers, under certain conditions, may 

 excavate beneath sea-level. 



The continental shelf of the Norwegian coast is 

 somewhat irregular, the depth of the edge below sea- 

 level differing much between 80m. and 300m., and 

 it is only at a few places that it is as deep as 360m. 

 (200 fms.). The great valleys and fjords of the land 

 are often continued as submarine valleys or fjords 

 across the submerged continental shelf, and at some 

 points they open out at its edge, forming distinct 

 incisions in the continental slope? but they are not 

 as a rule traceable beyond the 400 metres line, and 

 seldom even so far. 



The Norwegian submarine channel at the southern 

 end of Norway is regarded as part of the bed of 

 the ancient " Baltic River," which drained the 

 Baltic basin and southern Scandinavian tracts. It 

 is pointed out that Prof. Amund Helland attributed 

 this channel to the erosion of the Scandinavian 

 glacier during the Great Ice Age, and the author, 

 while admitting the influence of that glacier, con- 

 siders that the present relative depth is due to the 

 adjacent areas having been to a great extent filled 

 up with glacial drift. 



After dealing briefly with the regions of the Faeroes 

 and Iceland, and with the continental shelves of 

 Britain, France, and North America, the author sum- 

 marises his views on the general subject of the origin 

 of continental shelves. He discusses also various 

 explanations that have been given. 



Regarding the continental shelves as having been 

 shaped prior to the submerged valleys, and consider- 

 ing the great extent of these shelves, and the im- 

 probability of regular and extended vertical move- 

 ments of the lithosphere, the author in 1901 had 

 concluded that they must be due to oscillations of 

 the hydrosphere. He now considers that the general 

 level of the sea must have remained near its present 

 position, despite many oscillations of the land, during 

 the later geological periods. The eroded parts of 

 the continental shelves must have been developed 

 when the shelves were near to sea-level, owing their 

 features partly to conjoint action of subaerial erosion 

 and marine denudation, partly to deposition of 

 terrigenous waste, and even locally to organic 

 agents. 



Attention is directed to the extensive coast plat- 

 forms that occur in part a little below sea-level and 

 extend above it, evidencing small oscillations of the 

 shore-line. The Norwegian coast platform has a 

 surface formed chiefly by solid rocks, and the depres- 

 sions in it are not filled up to any great extent by 

 waste or glacial drift. This platform was in the 

 author's opinion formed by marine denudation after 

 the fjords and channels now traversing it were cut; 

 but the sculpturing may have been facilitated by 

 NO. 1823, VOL. 70] 



the clearing away of debris by glacial action. He 

 believes that marine denudation is most potent when 

 coasts are being slowly submerged ; but that the 

 Norwegian platform can hardly have been formed 

 during one period of submergence. These platforms 

 were formed in comparatively recent times, whereas 

 the continental shelves were to a great extent 

 developed during Pliocene and Pleistocene times. 



With regard to the oscillations of the land, the 

 author leaves the explanation in a somewhat vague 

 state, observing in conclusion that 



" whatever the causes of the oscillations of the 

 shore-line may have been, the above facts seem to 

 prove that, after each disturbance in the relation 

 between land and sea, the earth's crust has a 

 remarkably strong tendency to return to a certain 

 position of perfect equilibrium, which is probably 

 determined by the buoyanc)' of the crust floating on 

 the underlying magma." 



H. B. W. 



FOREST ENGINEERING. 

 A Manual of Forest Engineering for India. By C. G. 

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