42 AQUEOUS AGENCIES. 



America, through the Caribbean Sea and into the Gulf of Mexico, from 

 which emerging it runs with great velocity through the narrow straits 

 of Florida and thence under the name of the Gulf Stream along the 

 coast of North America, turning more and more eastward in obedi- 

 ence to the law already mentioned, until it becomes an eastward cur- 

 rent, £?, about 50° to 60° latitude ; and then stretches across to the coast 

 of Europe, and turns again southward to join the equatorial current. 

 A portion of it, however, in its eastward course turns northward, e, and 

 returns as a cold polar current hugging the shore of North America as 

 a cold wall to the Gulf Stream, and thus passes south. 



Geological Agency of Oceanic Currents.— The velocity of oceanic 

 currents is generally small, although, in the case of the Gulf Stream, at 

 the Florida Straits, it reaches almost the velocity of a torrent, viz., 

 three and a half to five miles per hour. The volume of water carried 

 by them is almost inconceivably great ; it is estimated that the Gulf 

 Stream alone carries many times more water than all the rivers of the 

 globe. According to Croll, it is equal to a current fifty miles wide and 

 one thousand feet deep, running at a rate of four miles per hour. The 

 geological agency of these powerful currents in modifying the bottom 

 of the sea by erosion may be, and by sedimentary deposit must be, 

 very important, though as yet comparatively little known. 



One of the chief functions of oceanic currents is the transportation 

 and distribution over the open-sea bottom of sediments brought down 

 by the rivers. By far the larger part of the debris of the land is cer- 

 tainly dropped near the shore, and marginal sea-bottoms are everywhere 

 the great theatres of sedimentation ; but, without the agency of marine 

 currents, none would reach open sea, all would be dropped near shore. 

 By the agency of these, however, the finer portions are carried and 

 widely distributed over certain portions of deep-sea bottoms. We 

 have undoubted evidence of this in some cases. Thus the sediments 

 brought down by the Amazon are swept seaward by a strong tide, and 

 then taken by the oceanic current which sweeps along that coast, and 

 carried 300 miles and deposited much of it on the coast of Guiana. 

 According to Humboldt, the same stream carries sediment from the 

 Caribbean into the Gulf of Mexico.* There is little doubt, too, that 

 much of the sediments brought into the Gulf of Mexico by the Gulf 

 rivers is swept along by the Gulf Stream, and a part of it deposited on 

 Florida Point and the Bahama Banks. The surface transparency of 

 the Gulf Stream is no objection to this view, as a little reflection will 

 show. Ocean-currents differ from rivers, in the fact that the former 

 run in perfectly smooth beds of still water. There are, therefore, no 

 subordinate currents from side to side, or up and down, whereby in river- 



* Lyell's Principles of Geology. 



