294 KRIDTJOF NANSEN. M.-N. Kl. 



As loiij^-- ,'is siicli fuDflaiiiciilai factors arc- unknown, it seems to be 

 somewhat liopclcss to make certain assumptions an*! then tr\- to finrl out 

 wliat can take place at the sin-face of the lithospliere. 



A more natural way max he t(; exannne a> clfjsely as possible what 

 has actually hapi)ene(l at tliis surface, anrl from this we may possibly draw 

 sonu' conclusions as to the state of the deeper strata. 



1 tliink that, for a better understanding of the isostatic problem, it 

 may be especially \aluable to study in all possible detail the vertical move- 

 ments of the crust in tlie rej^jions wjiere it has been depressed I>\' tlie load 

 (»f the ice-caps, and has again been u[)heaved after their removal. 



h^jr this kind of study there is at present hardly any better field than 

 l'\'nno-Scandia, and especiall}' the coast oi Norway, where the limits and 

 tlie process of the vertical nun-ements are now fairlv well established, 

 where tlie postglacial uphea\al of the lanrl is j)ractically completed, and 

 where there is a strandfiat indicating the le\el of the shore-line before 

 the land \\as depressed ])y the load of the ice. 



The Crust's Capacity of Isostatic Readjustment. 



I'here lias Ijeen much difference of opinion as to hfiw far the crust 

 may be able to approach its level of perfect isostatic equilibrium. Most 

 geologists have assumed that, owing to the rigidity of the crust, there can 

 only be a rough approximation to isostas}-. 



Hayford's computations seemed to indicate a high degree of local 

 isostasy of the continental crust inside even comparatively limited areas, 

 with a radius of no more than K) kilometres. He predicted that future 

 investigations would show tliat the horizontal extent which a topographic 

 feature may have witliout a corrcsponrling compensation of density would 

 be between one square mile (2.6 square kilometres) and one square degree. 

 The average vertical departure of the land surface from the elevation 

 giving perfect isostasy he stated to be less than j^ metres (250 feet). 



J. Barrell [1914, 191 5I although an adherent of the theory of isostasy, 

 does not consider local compensation to be probable, as he thinks that the 

 diameters of the areas of notable departure from normal gravity run up 

 to about 300 kilometres, and he and Putnam [1912] are of the opinion 

 that only regional isostasy may l)e attained inside areas with radial 

 distances of at least 167 kilometres. Even there Barrell thinks that the 

 distribution of compensation gives only a very rough approximation to 

 isostasy. 



Bowie [1917], however, finds that in mountainous regions regional 

 compensation with a radius of 59 kilometres satisfies the data as well as 

 does local compensation, but regional compensation to a distance of 167 

 kilometres does not do so quite so well, and he considers that local com- 



