444 



WASTE OF THE BANKS. 



[Ch. XIX. 



swamps 



waters 



sediment 



streets of the great city. 



The cause of the uniform upward slope of the river bank, 

 d b, above the adjoining alluvial plain is this : when the 



pass over the banks in the 

 ■flood season, their velocity is checked among the herbage 

 and reeds, and they throw down at once the coarser and 

 more sandy matter with which they are charged. But the 

 fine particles of mud are carried farther on, so that at the 

 distance of two miles, a thin film of fine clay only subsides, 

 forming a stiff unctuous black soil, which gradually enve- 

 lopes the base of trees growing on the borders of the 



swamps. 



Waste of the banks. — It has been said of a mountain 



torrent, that ' it lays down what it will remove, and removes 



what it has laid down ; ' and in like manner the Mississippi, 



by the continual shifting of its course, sweeps away, during 



a great portion of the year, considerable tracts of alluvium, 



which were gradually accumulated by the overflow of former 



years, and the matter now left during the spring-floods will 



be at some 



After the flood season 



j 



when the river subsides within its channel, it acts with 

 destructive force upon the alluvial banks, softened and 

 diluted by the recent overflow. Several acres at a time, 

 thickly covered with wood, are precipitated into the stream ; 

 and large portions of the islands are frequently swept away. 



Hall 



s 



that some years 



Mississ 



islands were numbered, from the confluence of the Missouri 

 to the sea ; but every season makes such revolutions, not only 

 in the number but in the magnitude and situation of these 

 islands, that this enumeration is now almost obsolete. Some- 



melted 



themselves 



is the more correct statement, the interval has been filled 

 up by myriads of logs cemented together by mud and rub- 

 bish." * 



One of the most interesting features in the great 



* Travels in North America, vol. iii. p. 361. 



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