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

: his
: rock
It is not easy to reconcile Jeffreys's views here with those
I have quoted above regarding the decline of strength
with increasing pressure in the crust. It is evident
iat if Jeffreys is right, the theory of isostasy is reduced to
shambles. But Daly presents a counterargument to show
iat he is not right. He suggests that at great depths the vis-
>sity would be so high that a comparatively
sudden ac-
imulation of strain from some cause could fracture the rock
if it were a solid. Laboratory experiments conducted by
ridgman have shown that solids subjected to pressures so
eat as to make them flow behaved in very peculiar fashion,
hey would flow, but the flow would, at times, be interrupted
f fracture and slip. Daly also quotes Gutenberg to the effect
iat ". . . Whereas at normal depths the accumulation of
rain is made possible by the strength of the rocks, at the
eater depths the high coefficient of viscosity is sufficient,
id no conclusion as to strength can be drawn" (97:403).
hus the counterargument is a strong one. All that is neces-
ry, in fact, both for the theory of isostasy and for the theory
: displacements of the crust is a thin layer of extreme weak-
*ss at the top of the asthenosphere, where the viscosity
ould be much less than at the greater depths.
According to Daly, Jeffreys adopted his view because he
>uld see no reason for the development of sudden stresses
the greater depths. Daly argues that this cannot settle the
atter; perhaps we shall eventually
discover a sufficient
Luse. Daly also says, when speaking of the earth's triaxiality,
iat it means "stress at depths of thousands of kilometers"
7:404). Putting two and two together, I would suggest that
ie deep-focus earthquakes result from the triaxiality, and
iat the stresses develop suddenly enough to exceed the lim-
5 of the viscosity at that depth and cause fracture, because
te triaxial bulges are not permanent features of the planet,
it recent deformations, which must set up strains at con-
ierable depths.
Archibald Geikie describes experiments done a long time