70 
OROGENY AND EARTH’S ROTATION 
As a counteractant of the centrifugal effects of rotation the 
force of gravitation, of course, serves to aid in the adjustment 
of all those minor and local crustal stresses which are a necessary 
consequence of the release of tangential tension. Curiously 
enough, normal faulting appears to be most frequent where we 
should least expect it. It seems, paradoxically, to be common 
where the manifestations of tangential compression are most ef¬ 
fective and impressive. Often it is found in broad plains-tracts 
where orographic disturbances are least in evidence. 
On the hypothesis of isostatic compensation gravity-faulting 
should be the predominant form of crustal adjustment. That it is 
not such is one of the strongest arguments yet urged against the 
universal applicability of the hypothesis. The Great Basin ranges 
are generally assumed to be par excellence examples of profound 
gravity-faulting. Since it is demonstrated that existing profiles 
are not the result of recent displacement genetic dependence can 
no longer be considered. That even the ancient faulting, such of 
it as is actually observed, may not be of the gravity type but of the 
thrust order seems never to have been surmised. Its critical ex¬ 
amination, with this possible aspect in mind, commands the most 
thoughtful attention. 
The prevalency of normal faulting in folded regions seems also 
to suggest that the phenomenon is really a direct result of the 
failure of orographic compression to sustain itself fully. Al¬ 
though a structure widely observed and easily explained on the 
hypothesis of a contracting nucleus its peculiar orographic relation¬ 
ships associate it with crustal adjustment that is really not in any 
measure dependent upon nuclear shrinkage. 
In the usual consideration of orographic compressive effects, 
both experimentally in the laboratory and observationally in the 
field, the treatment is that of simple lateral pressure such as is 
initiated in arriving at the crushing strength of rock. In a curved 
shell a large part of the crushing potentiality is converted into 
direct shearing action. The crushing stress is then concentrated 
along a plane instead of being diffused throughout the whole mass. 
Development of the shear in a crushing spherical shell necessarily 
proceeds from the inner concave face obliquely towards the outer 
convex surface. The line of direction of the localized stress, or 
rupture, beginning as a tangent on the concave face cuts the outer 
