680 T. C. CHAMBERLIN 
the same time heavier than the average, are inevitably bowed down- 
ward, unless these actions are thwarted by exceptional intercurrent 
agencies. This inevitable tendency is made the more certain of 
realization by the constant unloading of the lighter outward-bowed 
portions and the constant loading of the heavier sagged portions. 
This must hold true whether the process of deformation be con- 
tinuous or periodic. 
Now, if the process be strictly continuous, as must be the case if 
a nearly perfect and constant isostatic equilibrium is maintained 
between the oceanic and continental segments, and between their 
larger parts among themselves, the evolution of the continents may 
be followed with logical ease. The continents must rise as they are 
unloaded and the ocean basins must sink as they are loaded. A 
secondary result must be a counter movement of the suboceanic 
material by virtue of which it pushes beneath the eroded continents 
to compensate their loss. ‘The cbviousness of this appears at once 
if perfect fluidity, the condition of perfect isostasy, is substituted 
for the existing rigidity that masks the real trend of present ten- 
dencies. A perfect adjustment would then take place promptly by 
vigorous movements of the kind indicated. If a viscous condition 
were substituted for that of free fluidity, the process would be slower 
but none the less inevitable. If the viscosity were high, the process 
would be greatly delayed but would follow the same lines. If the 
inequalities of specific gravity hold for the larger topographic 
features, the tendency will be to reproduce them, for the most pro- 
tuberant portions are most eroded, in general, and suffer most from 
transportation. They are hence most lightened and must be most 
elevated in a strictly isostatic process. The continent is thus forced 
to reproduce itself automatically and, in theory, must continue to do 
so until the actuating agencies, the primitive differences in specific 
gravity, are removed. 
This alternative cannot apparently be accepted, for the grada- 
tional phenomena seem to be decisively against it. 
Ii we turn to the alternative view, and assume that the body of 
the earth is essentially crystalline, and is rigid up to the elastic limit 
of the most stressed points of the crystals, and that, aside from 
strain, the mass does not move until the elastic limit or the solution 
