(2) Both elevation and increase of land area resulted in a lowering of temperature, materially increased by the gradual development of great ice-sheets.
(3) These ice-sheets caused the development of subsidiary ice-sheets on their southern and western borders.
(4) The lowering of temperature in high latitudes increased the thermal gradient between equator and poles, resulting in:
(a) Increased snowfall, and hence increased glaciation on high mountains near the equator.
(b) Pluvial periods in the sub-tropical arid regions.
BIBLIOGRAPHY
Humphreys, W. J. “Physics of the air.” Philadelphia, 1920. [Pt. 4, pp. 556-629.]
Chamberlin, T. C. “An attempt to frame a working hypothesis of the cause of glacial periods on an atmospheric basis.” Journal of Geology (American), Vol. 7, 1899, pp. 545-84, 667-85, 751-87. [Carbon dioxide theory.]
Croll, J. “Climate and time in their geological relations.” London, 1875. “Discussions on climate and cosmology.” London, 1889. [Eccentricity of earth’s orbit.]