The Earth's Shifting Crust by Charles Hapgood - wire of information

THE SHAPE OF THE EARTH 159
ance and requiring readjustments. The crust of the earth,
being very thin as compared with the whole diameter of the
globe, is correspondingly weak, and usually gives way if much
material is accumulated on it at any one spot. The layer
under the crust is considered to be quite weak, and it permits
the crust to give way by flowing out from under. This
process is called "isostatic adjustment/' Funk and Wagnalls
define isostasy as follows:
Theoretical condition of equilibrium which the earth's surface
tends to assume under the action of terrestrial gravitation as affected
by the transference of material from regions of denudation to those
of deposition, and by difference of density of various portions of the
earth's mass near the surface.
In the last chapter we considered at length the effects of
the differences of density of rocks under oceans and con-
tinents, and how heavy rocks tend to reach equilibrium at
lower elevation, and lighter rocks tend to be found in con-
tinents and mountain chains.
According to the principle of isostasy, it has been widely
assumed that an icecap such as the one in Antarctica should
be in good isostatic equilibrium. Of course, if this were true,
the centrifugal effect of the icecap would be balanced at
every point by the force of gravity, and there would be no
effect left over to tend to shove the crust over the plastic
layer below. There might be a slight effect resulting from
the elevation of the continent and the icecap above the
mean earth surface, but it would be too small to consider.
Thus, our theory depends upon our ability to show that
isostasy has not operated effectively in Antarctica. The question
becomes one of estimating the difference between the
rate of growth of the ice sheet, the rate of yield of the crust,
and the rate of flow of the plastic layer under the crust. The
calculation must also take account of the amount of load
that may be borne by the crust, indefinitely, out of isostatic
adjustment, because of its degree of tensile strength. Campbell's
calculations of the centrifugal effect of the icecap, and
of the resulting bursting stress on the crust (Chapter XI),