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

350
EARTH'S SHIFTING CRUST
may just as well be looked at in the opposite way, as if the
icecap and crust stood still, or were under no horizontal
pressure, but force was being applied
to the butt end of the
wedge. Either way, the mathematics is the same. Campbell's
application of this principle to the problem of estimating the
bursting stress on the crust was discussed with physicists, including
Frankland, Bridgman, and Einstein (see below), none
of whom questioned its soundness.
After finding the quantity of the total stress on the earth's
crust produced by the centrifugal effect transmitted from
the icecap, Campbell reduced it to pressure per square inch
by dividing it into the number of square
inches in a cross
section of the earth's crust, assuming an average thickness of
the crust of about 40 miles. This estimate of the crust's thick-
ness is a liberal one, since some writers, including Umbgrove,
suggest that it may be no more than half as much. Since a
lesser thickness for the crust would mean a higher figure for
the bursting stress per square inch, an error in this direction
here may serve to counter the effect of the possible partial
isostatic compensation of the icecap, which we have disre-
garded in the tentative calculation of its centrifugal effect.
Thus, if half the icecap is isostatically compensated, but the
crust is only 20 miles thick, then Campbell's estimate of the
pressure per square inch will be unchanged.
Campbell found that the bursting stress on the crust per
square inch amounted to about 1,700 pounds (see p. 361). In
comparison with this, I found that the crushing point of
basalt at the earth's surface has been estimated, from laboratory
experiments, at 2,500 pounds. A number of points must
be considered in reaching conclusions regarding the possible
significance of these comparative figures. First, the crushing
strength of any rock is considered to be higher than its
tensile, or breaking strength. Thus, the tensile strength of
basalt, the principal constituent of the earth's crust, is probably
considerably closer to the estimated quantity
bursting
of the
stress. A second important consideration is that
the earth's crust is unequal in thickness and strength from