OROGENY AND EARTH’S ROTATION 
77 
tainment of such a monstrous form in nature the bottom would 
flow away and lose itself in the physically homegeneous mass in 
the zone of rock-flow. 
The overturn flexure is, of course, an extreme among plicative 
phenomena. Artificially it is sometimes produced in crushing 
experiments, as a direct result of mass-compression wherein the 
layers are too pliant to break. That the overturn fold is also a 
normal product of release of tangential tension is a wholly unex¬ 
pected attainment. Still more striking is the fact that, in the roll- 
paper experiments, overturn phenomena seem confined to a thin, 
outer shell, and do not extend with diminishing effect into the 
interior. Presumably in both nature and laboratory relief from 
load largely controls. 
The experimental reproduction of these broad basinal areas 
that correspond to the oceanic depressions of the geoid is accom¬ 
panied by results having curious significance. It points to the fact 
that we shall have to modify our basic conceptions concerning the 
major deformations of the earth’s crust. Instead of distin¬ 
guishing between continental elevations and oceanic depressions, a 
circumstance imposed by an overweening importance attached to 
the presence of the sea, an idea that has come down to us from 
time immemorial, the proper discrimination to be made is between 
the cordilleran ridges of the continental borders and the inter¬ 
vening savannahs, whether just above, or just below, the level 
of the sea. On this basis the tracts which we are accustomed to 
designate as oceanic depths and the low-level basinal interiors of 
the continents are arranged in the same tectonic category. Con¬ 
sideration of any such datum plane as sea-level may be with full 
propriety entirely neglected. The meridional disposition of the 
continents thus comes to be readjusted as relatively narrow oro¬ 
graphic ridges in place of broad basin shaped plateaus. 
In nature the maximum depth of the oceanic infold is about one- 
eight-hundredth of the earth’s radius; in the laboratory this broad 
infolding amounts to one-fifteenth of the spheroidal radius (fig¬ 
ure 7). Here, as elsewhere, the tremendous values of the vertical 
component occasioned by the release of tangential tension is as 
unlooked for as it is striking. 
As already intimated the noteworthy feature of the experimental 
results is the novel change in which they involve our conceptions 
