DEGRADATION. 185 



channel, both rock power and water power are employed, these two forces 

 acting in inverse ratio with the specific gravity of water and load; that is, 

 less water power is needed to drive the rock by the amount of the weight 

 of the water displaced by the rock, for to this extent, rock power is used. 



The amount of load which may be transported by the driving process, 

 or in other words, by water power, plus an amount of rock power, begins 

 with that degree of comminution which permits the load to be moved, and 

 is limited by the power of the water on one hand and by friction on the 

 other. And wherever the degree of comminution is such that the matter 

 is transported partly or wholly by the agency of flotation to such 

 extent as flotation is employed, the driving ceases and other limits are 

 imposed. 



We come now to the principal method of transportation ; that is, that 

 by flotation. Here the rock power is used in transportation, and the 

 water is the vehicle. If the matter to be floated is of the same or less 

 specific gravity than the water, a condition seldom obtaining, flotation is 

 perfect, and the water power is not used either in transportation or to pro- 

 mote flotation. But when the floating matter is of greater specific gravity 

 than the water, then the water power is used in promoting flotation. With 

 a given amount of water and sufficient supply of load, the extent to which 

 the water power will be utilized in promoting flotation will depend on two 

 conditions : First, the power of the water, which is measured by fall into 

 mass, or which may be expressed as velocity or again as declivity ; second, 

 it will depend on the relation which exists between the floating surface, or 

 surface presented downward, and the mass of each particle of the load. 

 In other words, it will depend on the specific gravity and comminution 

 of the load. If the specific gravity of the load is but little greater than 

 water, the velocity of the water becomes a very small factor, and the 

 amount which can be transported will be chiefly limited by the containing 

 capacity of the water, but this is a condition not actually found in nature. 

 The difference between the specific gravity of water and load is great, and 

 variable within such small limits that the variability may be neglected ; but 

 the relation between the floating surface and the mass of each particle of 

 load may be determined by another condition than that of specific gravity, 



