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

NORTH AMERICA AT THE POLE
he could see any logical alternative to crust displacement
as the explanation of these facts. He replied that he was persuaded
of the soundness of the method of crust radioelement
dating developed by Professor Urry, and that he saw no other
reasonable explanation of the evidence (see page 364). A third
line of evidence is that presented by Dr. Pauly, already dis-
cussed (Chapter III).
A fourth line of argument is developed by Lawrence Dil-
lon, who shows, first, that the essential condition governing
the growth of ice sheets seems to be not the average year-
around temperature, nor the amount of annual precipitation,
but the mean summer temperature (114:167). He points out
that no ice sheets form at the present time in areas with mean
summer temperatures of 45 F. or higher, and suggests that
they probably didn't in the past. He cites, as a good illus-
tration of this principle, the northeastern section of Siberia,
which is unglaciated despite the fact that it is the "cold pole"
of the world, and although it has a higher annual precipita-
tion than Greenland or Antarctica. But the summer tempera-
ture is high, and this he thinks is the controlling factor.
Dillon points out, next, that the existence of the Wisconsin
glacier would have demanded a decrease of 25 C. in average
summer temperatures as they exist now (114:167). But he
notes that according to Antevs the average temperature de-
crease in late Pleistocene time along the iO5th meridian in
southern Colorado and northern New Mexico as compared
with the present was only 10 F., while (according to Meyer)
the average temperatures during the glacial period in the
equatorial Andes were only 5 or 6 F. lower than at present
(114).
Thus Dillon shows that there was no uniform decrease of
summer temperatures during the glacial period. No world-
wide factor, such as variations in solar radiation, reduced the
temperature. The range of summer temperatures
would be
understandable if the ice sheet were a polar icecap, however,
and the range appears to require that assumption.