222 FKIDIjOK NANSEN. M.-X. Kl. 



There arc several processes conlinually at work causiiij^- changes in 

 the Y(jlume of the Ocean. The continual emission of water vapour from 

 the volcanos a^lds new water to the Ocean, while on the other hand water 

 is substracted from it I)y the alteration of rocks which hinds water chemi- 

 cally. These processes are slow, however, and the one more or less checks 

 the fjther. Tt is, therefore, harrlly probable that, during- the periods we 

 are here consiflerinJ^^ they have prcjducerl changes of sufficient importance 

 to account for the (jl)served shifts of the shore-line after the formation 

 of the strandfiat. 



The displacement of sea-water caused by a volcanic eruption on tlie 

 sea-floor would probably only cause a temporary rise of the general sea- 

 level, as the effect would ])robably be more or less readjusted bv the 

 isostatic movements of the crust under the Ocean. Crustal movements 

 changing the size or depth of the Ocean basin would naturally also cause 

 changes in the general sea-level, Ijut as these movements would be finally 

 controled by isostasy, it is hardly probable that they can have produced 

 appreciable changes during the periods we are discussing. The deposition 

 of sediment on the sea-floor may gradually raise tlie general sea-level, as 

 will be mentioned later; but this is also a slow process and is partly 

 checked by crustal sinking. 



Changes in the position of the poles would cause changes in sea-level. 

 But if the lowering of sea-level since the first formation of the strandfiat 

 should be thus explained, we would have to assume, that the pole has come 

 nearer to the regions of the strandfiat, which would involve the probability 

 that the climate has become more arctic since that time, which is exactly 

 contrary to what might be expected. Changes in the earth's centre of 

 gravity might also change the sea-level, but is probably so slow a process 

 that it would not help much to explain the changes under consideration. 

 The same is also the case with possible changes in the earth's rotation. 



The subtraction of water from, and the addition of water to, the 

 Ocean caused by the formation and melting of the great present and 

 Pleistocene ice-caps have probably produced the most considerable changes 

 in sea-level during comparatively short periods. 



Much water is now^ accumulated in the extensive ice-caps of the 

 Antarctic and of Greenland. 



According to Hess, the area of the Antarctic ice-cap is about 13 mil- 

 lions square kilometres and that of Greenland 1.9 million sq. km. If we 

 add to this the glaciers of the rest of the world, we get an ice-covered 

 area of about 15,156,000 sq. km. altogether. We do not know what the 

 average thickness of these ice-caps may be. The ice-caps of Greenland 

 and the Antarctic with their general level surfaces standing at altitudes of 

 2,000 and 3,000 metres and more above the sea, must obviously have quite 

 considerable thicknesses. If we assume the average thickness of the ice- 

 caps to be 600 metres, the melting of them would increase the average 



