230 KKIDTJOF XAN.SF.N. M.-N. Kl. 



assumed hy I't-nck ;iiii| tlic i^ciicral sca-lc\cl iiia\- |)ossiij|\- have been sunk 

 as mucli as kk) niclrcs hy llicir format i'^ii. \\ il bf assume! that 

 simultaneously there was a ^Teat cxlension of ice-caps in the southern 

 bemispliere, aiul tlie antarctic ice-cap liar] a f^reater thickness, T thouj^-ht 

 it "concci\ablc that tlie le\el of the Ocean was at times lowered as much 

 as 200 metres or even more". 



Ren;-inald A. Daly [1910, 1915, \). 173] has estimated that by the 

 nultinj;- of the I'leistocene ice-caps since their maximum development 

 "the general sea-le\'el lias been raiserl by an amount ran^-ini,'' betwe.-n 

 23 and 129 metres". He thinks that this minimum estimate is likely 

 to be too small, while the maximum estimate is too large. He thinks 

 a rise of sea-level of the order of 50 to 60 metres to be most probable. 



I think Daly's estimate is too low. It seems to me to be probable 

 that during their maximum development the T'leistocene ice-caps had a 

 greater average thickness and a greater extent than assumed even by 

 Drygalski and Penck. 



The Thickness of the lee-eaps. 



During the last glacial epoch Fenno-Scandia was depressed l)y the 

 weight of the ice-cap iirobably about 350 metres in its central region 

 about Bottenviken (the Gulf of Bothnia). If the specific gravity of the 

 plastic magma underlying the rigid crust be 3, the specific gravity of 

 the ice 0.9, and the thickness of the ice-cap /i, we have: 



//X0.9 = 350 3 -^ M 

 where M is a certain quantity due to the pressure counteracting the de- 

 pression created by the upheaval of the peripheral areas surrounding the 

 ice-caps, as will be mentionerl below. If for the moment we leave this 

 quantity out of consideration we have: 



H = ^^ ^ = 1 167 metres. 



0.9 



This is, however, a minimum value. First, it is improbable that the 

 land had been depressed to the full extent corresponding to the weight 

 of the ice-cap before the latter began to decrease. 



Secondly, there is considerable evidence to prove that the depression 

 of the areas covered by the ice-caps causeri an upheaval of the regions 

 surrounding the ice-caps. This upheaval will gradually spread outwards 

 from the ice-caps over wider and wider areas, and the elevation will thus 

 be reduced again very slowly. It is, however, obvious that as long as it 

 lasts, the weight of the elevated magma under these upheaved regions 

 will counteract to some extent the depression of the ice-caps, and will 

 reduce accordingly the depth to which the underlying crust can b? de 

 pressed bv their weight. The wave of upheaval surrounding a depressed 

 area will as it were temporarily raise the level of e(|uilibrium of this area 



