46 
The Colorado River 
included) which may fall in the high mountains, the canyons 
themselves being in the drier districts. It is also clear that if, 
by some chance, the precipitation of the high sources should 
increase, the corrasion of the stream-beds in the canyons would 
likewise increase and outrun with still greater ease the erosion 
of their immediate surroundings. On the other hand, if the 
precipitation in the arid surroundings should increase, the 
wearing down of the side walls would for a time—till covered 
by debris and vegetation—go on more rapidly till, instead of 
canyons of the Colorado River type, there would be deep, sharp 
valleys, or wide valleys, according to the amount of difference 
between the precipitation of the low lands and the high. Where 
the two were nearly the same, that is, a balance of precipita¬ 
tion,' the slopes might be rounded and verdure-clad, though 
this would depend on the amount of precipitation. On lower 
Snake River a change seems to be going on. The former can¬ 
yon-cliffs are covered by debris and vegetation, but in places 
the old dry cliff-lines can be discerned beneath like a skeleton. 
The precipitation there has not been great enough to destroy 
the old lines—only enough to mask them. 
The “inner gorge “ of the Grand Canyon appears to have 
been cut far more rapidly than the outer one, and at a much 
later period. Were this not the case there would be no inner 
gorge. It is a singular fact that some side canyons, the 
Kanab, for example, while now possessing no running water, 
or at best a puny rivulet, and depending for their corrasion on 
intermittent floods, meet on equal terms the great Colorado, 
the giant that never for a second ceases its ferocious attack. 
Admitting that the sharper declivity of the Kanab would en¬ 
hance its power of corrasion, nevertheless we should expect to 
see it approach the Grand Canyon by leaps and bounds, like 
the Havasupai farther down, but, on the contrary, there are 
parts that appear to be at a standstill in corrasion, or even fill¬ 
ing up, and its floor is a regular descent, except for the last 
three or four miles where the canyon is clogged by huge rocks 
that seem to have fallen from above. The maximum height of 
^ There could be a balance of precipitation and still very little snow- or rainfall, 
or they might be very great. 
