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

THE SHAPE OF THE EARTH 187
siderable period of time. The layer immediately under the
earth's crust is subjected to high pressure, and therefore,
although it is liquid, it may be stiff. The stiffness can be expected
to be least immediately under the crust, and to increase
with increasing depth.
However, it cannot be assumed that the viscosity imme-
diately under the crust is very great. Bridgman has pointed
out that it depends to a great extent on the particular chem-
ical composition of the rocks, which necessarily is uncertain
(50). Moreover, though pressure increases viscosity, heat
diminishes it, again differently for different chemical sub-
stances. It is difficult to estimate the net effect of the operation
of these opposite influences at any point under the crust.
Daly presents evidence that the viscosity of the asthenosphere
must be very low. He cites, first, evidence from the
edges of the area recently occupied by the Scandinavian icecap.
According to isostatic principles, viscous rock must have
flowed out from under the section of the crust loaded by the
icecap. If the rock was very stiff, Daly argues, it would not
have flowed very far, but would have upheaved the crust
around the fringes of the ice sheet. Evidences of such upheaval
should be observable, but there are none. He thinks
that there should have been an upheaval of the Lithuanian
plain, but none occurred. Hence his conclusion is that the
asthenosphere must have low viscosity: ". . . And there is
no apparent necessity for excluding the possibility of effec-
tively zero strength*' (97:389).
The meaning of this geological evidence appears to be
that the asthenosphere must be a true liquid in terms of
pressure applied over periods of the length required for the
growth of the Scandinavian icecap, which would be the same
length of time that we suppose would be involved in a displacement
of the crust.
As a second line of evidence for a weak sublayer, Daly
points out (as already mentioned) that in mountain making
the crust is folded to its full depth, that horizontal sliding has
to occur to permit this folding, and that horizontal sliding