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

VI :
THE
SHAPE OF THE EARTH
In the two preceding chapters we have considered the evidence
for displacements of the earth's crust provided by
mountain chains, earth fractures, volcanic zones, continents,
and ocean basins. We have had occasion to refer, a number
of times, to the effects of the force of gravity, and of the
earth's rotation, on the earth's crust. The understanding of
the theory of crust displacement presented in this book de-
pends entirely on a correct understanding of these two forces,
and of the operation of what we call the principle of isostasy.
The ideas are not difficult, provided certain essentials are
kept in mind.
j. Isostasy and the Icecap
The globe we live on is shaped primarily by the force of
gravitation. The weight of the materials of which it is com-
posed is greater than their strength, and they have therefore
been bent, broken, or forced to flow by this force until the
globe has become a sphere. It is not, however, a perfect
sphere. The earth deviates from being a perfect sphere because
it is rotating rapidly, and the rotation produces a cen-
trifugal
effect that tends to throw the materials outward at
right angles to the earth's axis, and against the force of gravity.
This slightly modifies the earth's shape, producing a
bulge around the equator and a flattening at the poles. The
earth modifies its shape until the two forces are in balance,
and the resulting oblate sphere is called the "geoid."
Of course, there is always a considerable amount of shift-
ing of materials going on on the face of the earth, rivers
bringing down sediment to the sea, icecaps growing and
melting, and these changes are constantly upsetting the bal-