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

THE ICE AGES 43
canic dust and carbon dioxide, and that is a displacement of
the crust. The extremely far-reaching consequences of a dis-
placement of the crust with respect to atmospheric condi-
tions, and the importance of the atmospheric effects of a
displacement for other questions, will be discussed in Chapters
VII and VIII.
The theories listed above were attacked by Coleman, who
complained that they were entirely intangible and unprovable.
He said:
Such vague and accidental causes for climatic change should be
appealed to only as a last resort unless positive proof some time becomes
available showing that an event of the kind actually took
place (87:282).
Another group of theories attempts to explain ice ages as
the results of changes in the positions of the earth and the
sun* These are of two kinds: changes in the distance between
the earth and the sun at particular times because of changes
in the shape of the earth's orbit, and changes in the angle of
inclination of the earth's axis, which occur regularly as the
result of precession. The argument that precession was the
cause of ice ages was advanced by Drayson in the last century
(117). The argument based on these astronomical changes
has been brought up to date in the recent work of Brouwer
and Van Woerkom (375: 147-58) and Emiliani (132). It now
seems that these astronomical changes may produce cyclical
changes in the distribution of the sun's heat, and perhaps in
the amount of the sun's heat retained by the earth, but it is
agreed, by Emiliani and others, that by itself the insolation
curve or net temperature difference would not be sufficient
to cause an ice age without the operation of other factors,
and so Emiliani suggests that perhaps changes in elevation
coinciding with the cool phases of the insolation curve may
have caused the Pleistocene ice ages. One weakness of this
suggestion is, of course, the necessity to suppose two inde-
pendent causes for ice ages.
There is another objection to be advanced against all