238 FRIDTJOF NANSEN. M.-N. Kl. 



The sinkinf4' of sc'a-lc\cl iluiiii^ tlic ^^^lacial pcriofls may, however, 

 hel]) lo explain ccrlaiii features of the continental shelves which seem 

 to iiKlicaie lliai tluy lia\c hci'u receiitl\- enier^cfj, c. ^. the occurrence at 

 dc'ptlis of 100 I0 150 metres of numerous water-worn shore fx;bbles ard 

 shells of littoral molluscs, Ixin^»- on or just hcneatli llie surface of the 

 continental shelf and harrlly covered hy later deposits. A great many river 

 channels and \alU'\s traversing the cont iiuiital slielves also indicate that 

 their surl'accs must luaxe heen emerged during sfjine recent perio'l, when 

 these channels were either formed or recjpeneil. 



In regions where the lanrl was covered by I'leislocene ice-caps the 

 continental shelves outside the coasts may also have been upheaved to 

 some limited extent wlien the land insifle was flepressed bv the weight 

 of the ice-caps Icf. H. Munthe, if;io. p. I20^)'. 



It is hardly ])ossil)le to compute the magnitude oi this periph.eral 

 upheaval. It seems probable that it reached its greatest heights during 

 the first period of the depression of the ice-covered region, when only a 

 comparatively narrow peripheral belt was pressed tip by the underlying 

 magma displaced by the depression. The height (jf this upheaved wave 

 gradualh' decreased again as the wave slowly extendecl its area outwards. 

 We have previously found that in the case of local equilibrium 



II >< 3 = d^o.<^ — // >■- 3 



where u is the average height of upheaval in the peripheral belt, d the 

 average thickness of the ice-cap, and /; the average height of the depression 

 under the ice-cap. This means that as tlie depression (li) gradually in- 

 creases the height of tipheaval (//) will decrease, and when // has reached 

 its full extent and 



/(X3 = c/> 0.9 



the upheaval ;/ will be zero, which will not happen before the whole crust 

 of the earth has regained its level of perfect equilil)rium. In that case 

 the upheaval of the crust compensating for its depression under the ice- 

 caps will have been entirely transferred to the floor of the Ocean the 

 volume of which was reduced by the formation of the ice-caps. 



In the case of the continental shelves of Norway and other glaciated 

 regions the development may have been the following: 



Bv the reduction of the volume of the Ocean there has been an im- 

 mediate sinking of the general sea-level, which during the maximum 

 development of the ice-caps may have amounted to 100 metres at least, 

 and perhaps to as much as 150 metres. By the gradual depression of the 

 interior areas of the land under the weight of the ice-cap the outer coast 

 and the region of the continental shelf have been upheaved. If this up- 

 heaval was as much as 50 metres, there may have been a negative shift 

 of the shore-line of as much as 150 or 200 metres. 



