FRAMEWORK OF ARIZONA 
233 
tains it is possible perhaps to trace it around them, for the Rockies 
sharply terminate near the southern Colorado boundary . Correla- 
tively, then, the general geological sections of New Mexico and 
Arizona become the most important and most illuminating of any 
on the continent. The one is recently presented; the other is here 
outlined. To those who are familiar with the stratigraphy of the 
Continental Interior these sections present no very serious diffi¬ 
culties; but the geology of the Southwest is usually attacked by 
those who never worked in the Mississippi Valley. 
Although many of the minor relief features of the region are no 
doubt partly or wholly water-formed, the general facial expression 
of the country is distinctly a kind little observed in the pluvial lands 
with which most of us are most familiar. The larger contrasts of 
surface relief must now be regarded as mainly wind-graved. Once 
clearly discriminated wind-sculptured topography is seldom mis¬ 
taken for any other sort. Its individuality is as strong as it is strik¬ 
ing. Wind-beveled surfaces are smoother than water-formed 
plains possibly can be. The rock-floors which characterize so many 
desert plains are phenomena as novel as they are unexpected. Des¬ 
ert ranges rising out of a sea of earth about impart characteristic 
form to the enisled landscape. It is the inselherglandschaft of the 
Germans on South Africa veldt. The girdled mountain attests the 
vigor of natural sand-blast action, and its maximum effectiveness 
is always at the plains line. Plateau plains of the desert manifestly 
represent former levels of the general plains-surface. The notable 
absence of foothills around the mountain bases appears to be an 
idiosyncracy of arid lands. 
Throughout the world gradation and planation usually pro¬ 
ceeds from the higher to the lower levels. Arid planation, how¬ 
ever, takes place uphill as well as downhill. Antigravitational 
gradation is unknown where streams corrade. High gradients of 
the intermontane plains and the strong pitch of valley axes which 
are displayed on every hand are not possible in regions where wa¬ 
ter-action is directly the reverse of plains forming. Of minor relief 
features now attributable to wind-abrasion in the lands of little 
rain, there are a multitude that are commonly ascribed to normal 
corrasion, but which can never have known the touch of stream. 
Upon all these the wind marks, when once pointed out, are unmis¬ 
takable. 
