66 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Alluvial Soils. The water falling on the ground and running 

 off on its surface, carries soil particles with it. Streams or rivers 

 take up particles of rocks or soil materials and carry them along. 

 In time of flood, when both the volume and velocity of the stream 

 are increased, this burden becomes much greater, since the carry- 



CULF or vex/ co 



Fig. 16. Sketch map showing the flood plain of the lower 

 Mississippi. U. S. D. A. 



ing power of water increases with the sixth power of the 

 velocity with which it moves. That is, a river moving at the rate 

 of four miles an hour may carry particles sixty-four times as 



