122 



PHYSICAL GEOLOGY 



RiierBanks /8S3 

 Bars etc. I&6) 

 Rti'er Banks 1655-6 



in time of flood, the river may 

 straighten its course by cutting 

 a channel across this narrow 

 strip, leaving horseshoe or oxbow 

 lakes, or bayous, which are soon 

 separated from the new and 

 shorter channel by deposits of 

 silt. Brooks tend to develop a 

 greater number of bends than 

 larger rivers, since they are 

 easily deflected by accidental 

 disturbances, such as a fallen 

 tree or a landslide, while a larger 

 river tends to obliterate its 

 smaller irregularities and to 

 develop the larger ones. As a 

 result, we find many close-set 

 meanders in small brooks, while 

 in large rivers there are a small 

 number of well-spaced meanders 

 which grow to large size before 

 Fig. no. — Meanders of the Mississippi they are cut off. Many ex- 

 River. The successive positions of the amples might be cited of cities 

 river in 1883, .895, and later are shown. j v ;,, , j he banks 



1 he movement of the meanders down- to . 



stream and their tendency to increase are of meandering rivers, which have 

 shown. (After Salisbury.) been left far inland by the cut- 



ting off" of the meanders on 

 which they were situated. Because of their changing channels 

 rivers make very poor political boundaries. 



In the course of time the " oxbow " lakes formed by the " cut- 

 offs " are destroyed, 



as they are apt to 

 be filled with sedi- 

 ment when the 

 stream is at flood, 

 and at other times 

 sand is blown in by 

 the wind, and vege- 

 tation takes root 

 there. 



\ 



FlG. in. — An oxbow lake formed by the cutting 

 through of the neck of a meander. 



