On the gexer\l Cause^^ of the Ocean-Currents. 29 



the straits between the Danish ishinds can occasionally display almost 

 the same saltness as in the Skagerack, as far as we can judge from the 

 observations, taken at the stations established by D:r A. Meyer. Several 

 causes may contribute to this, and more especially the velocity with 

 which the under-current passes through the Kattegat; moreover under 

 certain circumstances the character of the streams in the Skagerack and 

 Kattegat may be completely changed, so that the superficial current also 

 runs into the Baltic. 



As regards the peculiar conformation of the sea-bottom in the 

 parts we have just been considering, or the deep trough-formed channel, 

 which extends along' the Swedish and Norwegian coasts, it appears to 

 me almost beyond a doubt, that it is the effect of the under-current, 

 which has prevented there the deposition of the sediments, which now 

 cover the bottom of the North sea. This however was most probably 

 principally done at an epoch, when both streams, the upper muddy 

 stream of riverwater, as will as the under-current, ran with far greater 

 force than at present. The causes of such a state of the streams may 

 be found in the latter part of the North-European glacial period. The 

 quantity of river-water, which, when contemporaneously with the land's 

 sinking the glaciers melted, was thrown into the ocean, must then have 

 been far greater, and more loaded with mud than now, and the reaction- 

 streams, occasioned by that river-water in the ocean, must have been all 

 the more powerful for that the sinking of the land was not yet comple- 

 ted, and therefore the area for the section of the reaction-streams was 

 smaller. That changes of this sort, such as channelling of the sea-bottom 

 where the under-stream is rapid, depositions where stillness of the water 

 prevails, etc., are still in progress is not to be doubted, and it would 

 be an interesting geological problem to investigate more accuratl}- the 

 effects of this kind, produced by under-currents. 



The inner basins of the system before us, the Baltic, the Bothnian 

 sea and the Gulf of Bothnia, unlike those above described, are charac- 

 terized by uniform saltness at the surface and variable in t/te deeper 

 water '). The quantity of fresh water flowing hither is subject to less 

 sudden variations, and differences of saltness, which may take place at dif- 

 ferent spots, are more easily equated by the effect of winds in the ex- 

 tensive very slowly flowing surface. But the approach of the salt under- 



'} This is the case at least in the Baltic, but as regards the «Bottonhaf» and 

 the Gulf of Bothnia deep water observations are as yet wanting. 



