AQUEOUS AGENCIES. 



49 



streams : In rivers, besides the general current, there are 

 partial currents, from side to side and up and down, which 

 keep the stream turbid to the surface ; while ocean-streams, 

 running on beds and between banks of still water, have no 

 such partial currents. There is nothing to prevent sedi- 

 ments settling exactly as in still water. Thus ocean-cur- 

 rents usually carry sediments, if at all, only in their deeper 

 parts. Deep-sea deposits are undoubtedly of great im- 

 portance, but only recently have attracted much attention. 

 Submarine Banks. These are formed by checking 

 the velocity of sediment-laden currents, whether tidal or 

 oceanic. The checking may be caused by the meeting of 

 two opposing currents, or by the current passing through 



PIG. 25. Tides of the German Ocean. 



a narrow strait into a wide sea. In other words, subma- 

 rine banks are formed under the same conditions as bars ; 



LE CONTE, GEOL. 4 



