186 STRUCTURAL GEOLOGY. 



i. e., size; for the ratio between the floating mass of a body, or the surface 

 presented downward, and the mass of the body, increases with the diminu- 

 tion of a body. Then if the body is smaller, the ratio between the floating 

 surface and mass is larger; and hence comminution promotes flotation. If 

 this comminution is great, approaching complete or molecular comminution, 

 the velocity of the water again becomes a small factor, and the amount of 

 transportation chiefly depends on the containing capacity of the water ; but 

 as comminution is less and the size of the particles larger, some force must 

 intervene to promote flotation, and this is derived from the water power ; 

 and to sustain the same amount of flotation more of this force must be 

 utilized as the size of the particles increase. The amount of this force from 

 which must be drawn the supply in supporting flotation depends, cceterispar- 

 ibus, on the velocity or declivity, but practically the whole force is rarely 

 utilized. 



The extent to which this force is utilized depends upon many complex 

 conditions by which the motion in the flowing water may be transmitted to 

 the load. To float, the particles of rock must be suspended in the water, and 

 as they fall from suspension during the process of transportation, they must 

 be resuspended, so that the water power must be used in lifting, and this is 

 done by the creation of secondary currents in regurgitation, eddying, boil- 

 ing, &c., or movements in the water transverse or oblique to the direction of 

 the flow, all of which impede the flow. If the flow is perfect no lifting can 

 be done ; so these secondary currents are produced by locally diverting the 

 flow from its normal course, and this diversion to secure lifting must be di- 

 rectly or indirectly upward ; the greater and oftener this diversion the more 

 lifting will be done. In other words, we may say that water power is ap- 

 plied to the lifting of the particles and thus promotes flotation by hetero- 

 geneity of flow, and this heterogeneity of flow is induced by the heterogeneity 

 of channel in both horizontal and vertical direction, but chiefly in the lat- 

 ter. And in obedience to well known laws of friction this heterogeneity of 

 flow is greatly increased by intensifying the flow, or in other words, increas- 

 ing the velocity of the water ; and velocity is due to declivity. And that 

 heterogeneity of channel, which by producing heterogeneity of flow utilizes 

 the water power in lifting the load, is also due to declivity ; and hence it 



