94 
DYNAMICAL GEOLOGY 
pied, instead of continuing to rise, or at least to remain stationary, 
proceeds to sink. Indeed, sinking of this area is in evidence long 
before base-level is reached. At any rate, depression is active 
until the old erosion plane attains a level of more than two miles 
below that of the surface of the ocean. Where once lofty moun¬ 
tains pierce the sky marine sediments 10,000 feet in thickness 
accumulate. Despite the removal of its former great load the 
net result of the regional vertical movement is notably negative. 
Insinking of the earth’s crust in this region appears not to 
have taken place pari passu with extensive transference of sedi¬ 
ments. Cretacic depression manifestly initiates itself long prior 
to the beginning of sedimental loading, perhaps even before the 
mountains are completely demolished. Then, curiously enough, 
so soon as the enormous loading is finished the region uplifts 
again into lofty ranges as towering possibly as any which appear 
before or since. Instead of the sequence of events satisfying the 
isostatic equations the very reverse is true all through. Thus, 
crustal down-sinking succeeds to regional unloading; and orogenic 
upraising goes on under maximum load. Surely some orographic 
force other than the isostatic one is at work. 
In all four of these orogenic cycles the procedure is the same. 
Removal of load is not accompanied by further upraising. Rolling 
of oceanic waters over the tract follows regional unloading. 
Maximum areal loading is succeeded by great uplifting. Every 
stage meets with phenomena diametrically opposed to that which 
isostasy logically and vitally postulates. 
A noteworth shortcoming of the mathematical theory of iso- 
stacy is the circumstance that no distinction is made between the 
physical behavior under telluric stress of the thin crustal shell of 
rock-fracture and of the thick interior mass of rock-flow. In 
view of the fact that any depression or insinking of the crust due 
to sedimental loading occasions removal of an equal thickness ' 
from the bottom of the affected prism through direct flowage it 
many be questioned whether any such rock-prism appreciably 
changes its specific gravity, so slightly in this respect do rocks 
in the zone of fracture differ from one another. What really, 
then, is mistaken for floatage phenomena is adjustment in the 
earth’s crust of the effects of centrifugal force arising out of a 
retardation of rotation of the geoid. 
