RESIDUAL, GRAVITY-LAID, WATER-LAID DEPOSITS 33 



of rest of the detritus. The downward movement does not stop here, 

 for there is a certain amount of " creep " due to freezing and thaw- 

 ing, and the action of water aided by gravity (Fig. 23) that ulti- 

 mately reduces the slope so that it may be cultivated. These talus 

 slopes are small in extent and are of very little agricultural value 

 because of their stony character. 



2. Sedimental or Water-laid Soils. The material forming 

 these deposits has been carried in suspension or rolled along the 

 beds of streams for a greater or less distance from their place of 

 origin. When a body is immersed in water, it los.es weight equal 

 to the weight of the water displaced by it. This buoyant effect 

 enables fine particles to remain in suspension for a long time and 

 renders coarser material more easily moved than when in the 

 atmosphere. The total amount of material carried by running 

 water varies as the fifth 2 power of its velocity while the size of 

 particles carried varies as the sixth power, so that doubling the 

 velocity increases the amount of material thirty-two times and the 

 size of material carried sixty-four times. If the velocity wero 

 trebled the amount is increased two hundred and forty-three and 

 the size is increased seven hundred and twenty-nine times. Then 

 if a given current carries particles .1 mm. in diameter doubling 

 its velocity enables it to carry material (i.4 mm. in diameter, or 

 trebling the velocity enables it to carry particles 72. !> mm. in 

 diameter. The following table shows the character of material that 

 may l>e carried or 'swept along by the current. 



The Material Carried by Water of Varied Velocity* 



Inches per Miles per 

 second hour 



3 0.170 will just move fine clay. 



(5 0.240 will lift fine sand. 



8 0.4545 will lift sand as coarse as linseed. 



12 0.08 1U will sweep along line gravel. 



24 1.3038 will roll rounded pebbles 1 inch in diameter. 



30 2.045 will sweep along slippery, angular stones the 



size of an egg. 



Another factor in the transportation of soil material is given 

 by King. 4 When a particle is immersed, it attracts a film of water, 

 which becomes an essential part of the particle, moving with it 

 wherever it goes. The specific gravity of soil particles is approxi- 

 mately 2.65. The immersed solid-liquid body has such low specific 

 gravity that* very little force is required to keep it in suspension 

 and so it becomes possible for a particle to bo carried hundreds of 

 miles. This adherent film averages about .f>r> mm. in thickness. T>y 

 computation we find that a clay particle .001 mm. in diameter with 

 3 



