G. K. Gilbert—The Colorado Plateau Province. 91 
n 
Weathering 1s not directly influenced by slope, but it is 
o 
reached indirectly through transportation. lution and frost, 
(2.) Other things being equal, erosion is most rapid when the 
eroded rock offers least resistance; but the rocks which are most 
favorable to one portion of the process of erosion, do not neces- 
sarily stand in the same relation to the others. Disintegration 
by solution depends in large part on the solubility of the 
rocks, but it proceeds most rapidly with those fragmental rocks 
of which the cement is soluble, and of which the texture 1s 
Open. Disintegration by frost is most rapid in rocks which ab- 
sorb a large percentage of water and are feebly coherent. Dis- 
integration by mechanical wear is most rapid in soft rocks 
Transportation is most favored by those rocks which yield by 
disintegration the most finely comminuted debris 
(8.) The influence of climate upon erosion is less easy to 
formulate. The direct influences of temperature and rainfall 
are comparatively simple, but their indirect influence, t rough 
vegetation, is complex, and is in part opposed to the direct in- 
fluence of rainfall. 
emperature affects erosion chiefly by its changes. Where 
the range of temperature includes the freezing point of water, 
frost contributes its powerful aid to weathering ; and it is only 
where changes are great and sudden that rocks are cracked by 
their unequal expansion or contraction. 
