

346 



SINUOSITIES OF EIVERS. 



[Ch. XV. 





portion of these rocks began to be acted upon by rain 



summer 



and other causes. I could cite other regions in Georgia 

 and Alabama where the cutting down of the trees which 

 had prevented the rain from collecting into torrents and 

 running off in sudden land-floods, has given rise to recent 

 ravines from 70 to 80 feet deep in Tertiary and Cretaecous 

 formations. 





>/ 



— In proportion as such valleys are 



widened, sinuosities are caused by the deflection of the 

 stream first to one side and then to the other. The unequal 

 hardness of the materials through which the channel is 

 eroded tends partly to give new directions to the lateral force 

 of excavation. When by these, or by accidental shiftii 

 the alluvial matter in the channel, the current is made to 

 cross its general line of descent, it eats out a curve in the 

 opposite bank, or in the side of the hills bounding the valley, 

 from which curve it is turned back again at an equal angle, 

 so that it recrosses the line of descent, and gradually hollows 

 out another curve lower down in the opposite bank, till the 

 whole sides of the valley, or river bed, present a succession of 



salient and retiring angles, 

 from a straight course bv 



Am 



o 



mountainous regions to widen the valleys through which 

 they flow, may be mentioned the confluence of lateral 

 torrents, swollen irregularly at different seasons by partial 

 storms, and discharging at different times unequal quantities 

 of sand, mud, and pebbles, into the main channel. The 

 curves formed by the winding of rivers in their alluvial plains 

 increase in magnitude in proportion to the volume of the 



rivers. 



Mississij 



New Orleans, near Port Hudson, makes a circuit of 



twenty-six miles and returns to within one mile of the point 

 from which it set out ; this occurred at Eaccourci, which I 

 visited in 1846/ and in the same year, immediately below 

 the city of New Orleans, where the stream is about three- 

 quarters of a mile wide, there was a bend of eighteen miles, 

 after which the river came within five or six miles of the 



* Second Visit to the United Slides, vol. ii. p. 193. 







