174 



A YEAR IN SCIENCE 



time, it can carry stones sixty-four times as heavy as 

 at the normal stage, for 2x2x2x2x2x2 = 64. Thus as 

 the velocity of some mountain streams is increased 

 many times during floods, we may easily account for 



Copyright 7020 T)y Perry Pictures Co. 

 FIG. 67. Arroyo Seco River, Sierra Madre Mountains, Southern 



California. 



Stones serve as tools for cutting river beds deeper and broader. 

 In this process the stones become smooth and rounded. 



the marvelous power that these streams exhibit in 

 transporting enormous boulders great distances. 



The amount of sediment carried by streams is enorm- 

 ous. It is calculated that the Mississippi River carries 

 more than 1,000,000 tons of rich soil into the Gulf of 

 Mexico every day. The yearly loss to the country of 

 this soil is said to be about $500,000,000. As this is a 

 very serious loss, and in some parts of the country soil 



