TERTIARY HISTORY OF THE TENNESSEE RIVER 203 



the Alabama River. It follows from this that the Upper Tennessee 

 basin must formerly have drained out through the Coosa- Alabama 

 system by a river occupying the old valley across the divide south of 

 Chattanooga, that stream having since been diverted westward 

 through Walden Ridge by a branch of the Sequatchie River. 



If all of the sediment laid down in the sea opposite a given river is 

 brought there by that river alone, then this evidence would indeed 

 seem conclusive in favor of the theory of capture. It is believed, 

 however, that such an assumption would be contrary to what we 

 know regarding the behavior of river-brought sediment under marine 

 control. It would imply an absence of all appreciable transportation 

 and distribution under the action of oceanic and littoral currents, 

 the well-recognized drift to leeward produced by storm-waves, and 

 the small but long-continued action of the tides. That these agencies 

 have a very important influence seems well established by a large 

 number of concrete observations. According to LeConte, the sedi- 

 ment brought down by the Amazon is carried seaward by a strong 

 tide, taken up by the ocean currents, swept to a distance of 300 miles 

 or more, and much of it deposited on the coast of Guiana (p. 40). 

 It is estimated that the Nile carries out past its delta 36,600,000 

 cubic meters of silt every year. Yet this enormous amount of sedi- 

 ment apparently does not add to the seaward extent of the delta, 

 because of a powerful marine current that sweeps past the coast and 

 transports the sediment far eastward, where it is finally thrown down 

 along the coast of El Arich desert. Over a portion of Blake plateau, 

 southeast of Georgia, between depths of 100 and 600 fathoms, the 

 bottom seems to be swept clean of mud, ooze, and almost so of living 

 species. Agassiz attributed this to current action. And, again, 

 LeConte tells us that the sediments brought into the Gulf of Mexico 

 by the Gulf rivers are swept along by current action, and in part 

 deposited on Florida Point, and the Bahama Banks (p. 40), while 

 Mr. White (p. 36) refers to the fact that "after the formation of the 

 Nita Crevasse in 1890, fine mud from the Mississippi was deposited 

 in Mississippi Sound even up to the mouth of Mobile Bay, driving 

 out the fish and killing the oysters " (E. A. Smith et al., p. 30). Account 

 must also be taken of the numerous well- recognized cases of trans- 

 portation due to the set or drift given by storm-made waves and 



