48 DYNAMICAL GEOLOGY. 



Wilt or (jjirrietl by this ocean-stream is probably greater tban 

 that of all the rivers in the world. It is equivalent to a 

 stream fifty miles wide, one thousand feet deep, and run- 

 ning at a rate of three miles per hour. Its extreme 

 velocity, where it passes through the Straits of Florida, is 

 four to five miles per hour. 



Geological Agency. Oceanic streams run on beds and 

 between banks of still water, and therefore, probably, 

 have no erosive agency, but they are important agents in 

 the transportation and distribution of sediments. All the 

 debris of land-surfaces are brought by rivers to the water- 

 front and dumped there. Tides, in their retreat, may take 

 these seaward a few miles, but these also soon lose their 

 velocity and drop their freight. Were it not for oceanic 

 currents, therefore, the whole debris of land-surfaces 

 would be dropped within thirty to fifty miles of the shore- 

 line. As it is, nine tenths are so dropped. Marginal 

 sea-bottoms are, therefore, the great theaters of sedimenta- 

 tion. Nevertheless, a small portion of finest sediment is 

 carried within reach of oceanic currents, and by them 

 strewed broadcast over portions of deep-sea bottom. 



We find good examples of this in the course of the Gulf 

 Stream. The sediments of the Amazon may be traced 

 from its mouth seaward for a great distance. It is then 

 taken by oceanic currents and carried northward, and 

 much of it deposited on the coast of Guiana, three hun- 

 dred miles distant, and the remainder into the Caribbean 

 Sea. According to Humboldt, much sediment is carried 

 from the Caribbean into the Gulf of Mexico. The stream 

 receives there also, possibly, contributions from all the 

 Gulf rivers, especially the Mississippi, and may deposit 

 these again along the coast of Florida and the Bahama 

 Islands. 



The surface transparency often conspicuous in oceanic 

 currents is no evidence against their carrying sediments ; 

 for there is this difference between rivers and oceanic 



