78 SECTIONAL ADDRESSES 
The most valuable contributions towards a solution are coming at 
present from the meteorologists, and Dr. Simpson and Dr. Brooks have 
each made important suggestions. ‘There is, as Dr. Simpson says, ‘ no 
formulated meteorological opinion,’ but he has personally come to a 
certain conclusion.5*? ‘Throughout geological time, he continues, there 
must have been climatic zones. The climate in a zone depends on two 
factors—the intensity of solar radiation, and the distribution of land 
and water. A study of the present climatic zones shows that the mean 
temperature in it is not affected by the distribution of land and water, 
though locally a range of 5° C. from the mean of the zone may occur. 
It is the annual range of temperature that is chiefly affected by the distri- 
bution of land and water. On these grounds he concludes that ‘ no 
change in the distribution of land and sea alone could have produced the 
large changes in climate shown in the geological record.’ 
Increases in solar radiation will cause (a) a greater temperature gradient 
from pole to equator, (b) an increase in the general circulation of the 
atmosphere, (c) increase in cloud and rainfall, (d) an increase in the 
mean temperature of all zones. Again he concludes that there is no 
evidence of sufficiently large changes in solar radiation to account for the 
facts of geological climates. Consequently, only a theory of continental 
drift will suffice. 
Dr. Brooks thinks that Simpson has under-estimated the effects of 
ocean currents. He attacks the problem from another point of view, 
namely, the question of Ice Ages. He shows that once an ice cap com- 
mences, it spreads rapidly, for its cooling effect increases with its area ; 
but a critical point occurs beyond which the effect is not proportional to 
the area, and consequently the ice cap finally terminates. He concludes 
then that the conditions that determine the temperature of Arctic and 
Antarctic areas is not the distribution of land and water, but the distribu- 
tion if there were no ice. ‘The most favourable distribution of land and 
water for high polar temperatures is a series of long narrow islands ex- 
tending meridionally from high to low latitudes, and separated by wide 
deep seas. The worst distribution would be lands stretching parallel 
to the lines of latitude. There are, in his opinion, only two possible 
polar climates, a mild type and a glacial type. Since the lands have 
mostly stretched from high to low latitudes, the mild type is normal and 
glacial periods exceptional. 
Wilhelm Ramsay, of Helsingfors, in 192454 advocated an increase in 
relief to explain glaciations, as others had done in former years. Orogenic 
movements, he claims, have preceded the chief periods of glaciations. 
The Caledonian, Hercynian, and Alpine periods of orogenic disturbance 
have each resulted in glaciations in the succeeding epochs. Mountain 
chains increase radiation because the layer of air above them is thinner, 
consequently there are colder conditions developed, and snow may 
accumulate, causing a still further reduction of temperature. Again, 
the greater amount of snow involves a removal of water from the ocean, 
and the lowering of level may amount to as much as 130 metres if we 
53 * Discussion on Geological Climates,’ Proc. Roy. Soc., 1930. 
54 Geol. Mag., 1924. 
