OROGENY AND EARTH’S ROTATION 
79 
axes. Not a single instance is recalled in all the world where 
a monoclinal flexure runs in the direction of the earth’s rotation. 
Applying the experimental principles established to the earth a 
rational scheme of orogeny seems to be evolved. That there 
should be in the outer thin shell of rock-fracture a slow, differ¬ 
ential lagging of the different strata, somewhat analogous, per¬ 
haps, to the retardation of the atmospheric shell, whence rise the 
trade-winds, is one of the necessary consequences of a diminishing 
rate of terrestrial rotation. Aside from the time-factor the main 
difference between the two phenomena is that one shell is homeo- 
geneous in its makeup; while the other is heterogeneous in its 
composition. 
Were the outer crust of the earth homogeneous in its resisting 
qualities as is its interior the great mountain chains would prob¬ 
ably all be disposed along more or less regular meridional lines. 
As it is, with thick resistant terranes interspaced with vast weak 
shale belts the release strains are necessarily irregularly deflected 
and the lines of maximum compression are directed every which 
way. Under such conditions it is small wonder that no satisfac¬ 
tory crystallographic symmetry among the mountain trends of the 
earth is ever discerned. Only on the hypothesis of a collapsing 
geoid is crystallographic form of interest. 
In a rock-shell of diverse resisting qualities in its various parts 
it is obvious that secular retardation of the earth’s rotation would 
set up stresses which would only find relief from time to time as 
there would be forward creeping of the hard or resistant layers. 
Release of this cumulative stress might find expression in local 
crustal rupture which is commonly called thrust-faulting, or by 
orographic folding of strata. The meridional corrugation would 
be also profoundly affected by the change in the ellipticity of the 
earth’s figure occasioned by the reduction of the rate of rotation. 
The feature which brings the precessional hypothesis of tectonics 
to a working basis is the fact that the stresses are capable of re¬ 
duction to an astronomical foundation and to exact mathematical 
expression. The mount of differential creep within the zone of 
rock-fracture which has taken place since Devonic times, or dur¬ 
ing a period of fifty millions of years, is indicated by the value of 
the retardation of the earth’s rotation since that ancient date when 
the sidereal day was only about one-fourth as long as at present. 
