190 



GEOLOGY. 



Flood-plain meanders. 



path. The water flowed eastward through Lakes Pontchartrain and 

 Borgne, and entered Mobile Bay with such volume, velocity, and load 

 of mud, as to destroy for a time the oyster and fish industries of that 

 locality.^ 



Cut-and-fiU. — A stream with an alluvial 

 plain is likely to meander widely (PL XVI). 

 In general terms this may be said to be 

 the result of low velocity, which allows it 

 to be easily turned aside. Were the course 

 of such a stream made straight, it would 

 soon become crooked again. The manner 

 of change is illustrated by Figs. 180 and 

 181. If the banks be less resistant at 

 some points than at others, as is always 

 the case, the stream will cut in at those 

 points. If the configuration of the chan- 

 nel is such as to direct a current against 

 a given point, a (Fig. 180), the result is 

 the same, even without inequality of 

 material. Once a curve in the bank is 

 started, it is increased by the current 

 which is directed into it. Furthermore, 

 as the current issues from the curve, it 

 impinges against the opposite bank and 

 develops a curve at that point. The 

 water issuing from this curve develops 



Fig. 180. — Diagram illustrating another, and SO On. 



an early stage in the develop- Otipp c-tnrtprl ihp mrvpq or meflndera 

 ment of meanders. The shaded ^^^^ starteo, xne curves or meanaers 



part represents the area over tend to become more and more pro- 

 which the stream has worked. ,. -r^. ^^rk j-ioi\ 



nounced (compare Figs. 180 and 181). 



In the case represented by Fig. 1, Plate XVI (Missouri River near 



Brunswick, Mo.) the narrow neck of land between curves is almost 



cut through. When this is accomplished, the stream will abandon 



its wide curve. A later stage in the process is shown in Fig. 2, 



Plate XVI (the Osage River near Schell, Mo.). 



iL. C. Johnson. Bull. Geol. Soc. Am., Vol. II, pp. 20-25, 1891. 



