200 



GEOLOGY. 



axis, where the flow is strongest, the movement diverges more or less 

 to right and left. Since the velocity of the diverging water is reduced 

 more rapidly than that of the water which follows the axis of flow, 

 deposition is likely to take place fastel* on either side of the axis than 

 along the axis itself. The result is that the extra-debouchure current 

 tends to build up levee-like ridges on either side, making a sort of sluice- 

 way for itself. This sluice-way is gradually extended seaward, and at 





SCALE OP MiCEd 



Fig. 190. — The terminus of the delta of the Mississippi. (C. and G. Survey.) 



the same time gradually filled. As its capacity is reduced, more and 

 more of the water flows over its sides. Presently the escape of the 

 water over the little side-levees will develop a break at some point, 

 and a line of distinct flow then diverges from the main current. This 

 distributary repeats the history of its main. Thus the processes of 

 levee-building, channel-filling, and levee-breaking follow one another, 



