A STUDY OF COBBLE ABRASION 



509 



The cobbles in the drums roll continuously down the upgoing 

 side of the barrel, practically under water, at its rate of peripheral 

 travel (i .84 miles per hour or 44 . 16 miles per day). 



The question of how closely the rolling of cobbles down this 

 incline simulates the actual travel of similar materials in streams 



Fig. 2. — Relation of rate of wear to size of cobble 



has not yet been carefully investigated. The chief difference, 

 however, will be a constant difference in rate of wear, i.e., i mile in 

 a drum equals more or less than i mile in the stream, and will not 

 detract from its value in making comparative studies. 



It is planned later to make experimental studies of wear 

 during actual transit in streams under natural conditions and 



