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

i86 EARTH'S SHIFTING CRUST
diminution of the tensile strength and rigidity of the rock.
The decline of strength continues to the bottom of the crust.
Dr. Jeffreys remarks: ". . . At some depth ... it begins to
decrease and may be a tenth of that of surface rock at a depth
of 30 miles. . . ." (238:202).
At the bottom of the crust, perhaps about 36 miles below
the surface of the earth, an important change of state
apparently takes place. The heat reaches the melting point
of the rocks, and the rocks can no longer crystallize. Since the
strength of rocks depends mostly upon a structure of strong,
interlocking crystals, the change of state implies a disappearance
of strength. For this reason Professor Daly considers the
asthenosphere to be "essentially liquid/'
". . . For it is
hardly to be doubted that a rock layer, too hot to crystallize,
has only a minute strength, or no strength whatever" (97:399-
400).
Jeffreys is in agreement that the melting point
of rock
should be reached about 36 miles down (238:140), judging
from the heat gradient.
If it were only a question of the crystalline or noncrystalline
structure of the rock, we would readily conclude that
the asthenosphere could offer no serious resistance to the dis-
placement of the crust. The crust would be truly (to use Einstein's
term) a "floating crust."
But we must also take into account another quality of mat-
ter, which is viscosity. Materials possess varying degrees of
viscosity. Viscosity can make a liquid act like a solid. If, for
diver hits the surface of the water at a bad
example, a high
angle he may kill himself, because the water, though liquid,
requires time to flow, and if the impact is too sudden there
is no flow and the liquid acts as a solid. Tar is an example
of a more viscous substance. Taffy candy is highly viscous,
and can be cut with scissors, and yet, given a certain amount
of time, it will flow like a liquid. The effect of pressure on
different substances is to increase their viscosity, to make
them stiffer. They will then resist sudden shocks better, but
will flow like liquids if subjected to steady pressure for a con-