90 G. K. Gilbert—The Colorado Plateau Province. 
i i : Is are mud, 
The effective force is that of the current; the too nag 
sand, and bowlders. The most Important of them is eer yes 
chiefly by the impact and friction of Erie of sand that tl 
rocky beds of streams are disintegrated. 3 
Sivesias of clear water corrade their beds by solution. Muddy 
streams act partly by solution, but chiefly by attrition. 
Streams transport. the combined products of corasion ay 
weathering. A part of the debris is carried in so ee a 
part mechanically. The finest of the undissolved detri ee a4 
im suspension ; the coarsest is rolled along the bottom; a ee 
is a gradation between the two modes. There is a ¢ 
“ints: bbles, 
transportation is thereby accelerated. Bowlders and pe | 
while they wear the Micasisbeal by pounding and be 
worn still more rapidly themselves. Sand grains are bile a 
broken by the continued jostling, and their fragments 0 ne: 
suspended mud. Finally the detritus is all more or les 
solved by the water, the finest the most rapidly. - hy chin 
_In brief, (1) weat ering is performed by solution ; Ve vine 
of temperature, including frost; by rain beating; and by veg' 
tation. ‘ 
(2) Transportation is performed chiefly by running water. 
(3 i 
Corrasion is performed by solution, and by mechanical 
Corrasion is distinguished from weathering chiefly by Bo 
eluding mechanical wear among its agencies, and the py 
ance of the distinction will be apparent when we come to 
sider how greatly 
modifying conditions. ‘pee 
n the region of cafions, the rogress of corrasion ere 
Stripped that of Weathering, and to discover what con r A 
have determined this result, is to solve the problem o 
cations, 
B. The chief conditions which affect the rapidity of erosion 
are (1) declivity, (2) character of rock, and (8) climate. ak 
(1.) In general, erosion is most rapid where the slope is — 
but weathering, ‘trans ortation and corrasion are affecte 
different ways and in different degrees, 
ning water, and with that sons increase in its power to transport , 
undissolved detritus, 
The abili 
enhanced by ; 
mechanical wear kee the: 
may even increase more rapidly. For not only does the bot- 
Oes increase in the velocity of run- 
