DEGRADATION. 189 



cess; but the difference between greater or lesser rainfall is plainly manifest 

 in the topographic features produced little rainfall giving angular reliefs ; 

 much, rounded reliefs. 



Neglecting such a hypothetic condition as no rainfall, we have in nature 

 to consider only greater or lesser raiiffall. With greater rainfall we have a 

 greater power, but a lesser utilization of the power; with lesser rainfall we 

 have lesser power, but greater utilization; and in these varying conditions, 

 just where maximum degradation is found I am not able to state. Hence, 

 in the process of degradation which. I have called erosion, we have simply 

 to consider declivity, with exceptions so minute that they may be neglected. 



Now, it must be taken into consideration that this is the most import- 

 ant method of degradation, as it acts everywhere on the dry land; but, 

 because its operations are so greatly diffused, being universal in its action 

 on dry land, it is so subtle and minute in its manifestations within any area 

 which may come immediately under the eye that its efficiency is apt to be 

 underrated. 



CORRASION. This is the action of waters gathered into streams where 

 their operations are confined to more limited areas, that is, along the chan- 

 nels of such streams. Here the material supplied from the surrounding 

 surfaces by erosion is further transported by the streams, and in the process 

 of transportation becomes the instrument used in disintegrating the stream 

 beds; and the material thus disintegrated is added to that furnished by ero- 

 sion, and with it is transported by the streams, and this added material also 

 becomes an instrument of disintegration. 



The force used in disintegration is rock power and water power; load 

 is the instrument, water the agent. All processes of solution are neglected. 



The force of rock power and water power is measured by mass into 

 fall, and this may be considered as declivity; the specific gravity of the 

 instrument not being greatly variable may be neglected. There are other 

 conditions of instrument, such as hardness and angularity of particles, which 

 for any given particle might be of value in determining its efficiency; but, 

 in the multifarious particles of diverse hardness and form, a general average 

 will be established for streams, variable within such small limits that these 

 conditions also may be neglected. The only condition of instrument of 



