CHAPTER VIII. 
THE CAUSES OF GLACIAL EPOCHS. 
Various suggested causes — Astronomical causes of changes of Climate — 
Difference of Temperature caused by varying distance of the Sun — 
Properties of air and water, snow and ice, in relation to Climate — 
Effects of snow on Climate — High land and great moisture essential to 
the initiation of a Glacial Epoch — Perpetual snow nowhere exists on 
lowlands — Conditions determining the presence or absence of perpetual 
Snow — Efficiency of Astronomical causes in producing Glaciation — 
Action of meteorological causes in intensifying Glaciation — Summary 
of causes of Glaciation — Effect of clouds and fog in cutting off the 
Sun’s heat — South Temperate America as illustrating the influence of 
Astronomical causes on Climate — Geographical changes how far a 
cause of Glaciation — Land acting as a barrier to ocean-currents — The 
theory of interglacial periods and their probable character — Probable 
effect of winter in aphelion on the climate of Britain — The essential 
principle of climatal change restated — Probable date of the last 
Glacial Epoch — Changes of the sea-level dependent on Glaciation — The 
planet Mars as bearing on the theory of excentricity as a cause of 
Glacial Epochs. 
No less than seven different causes have been at various times 
advanced to account for the glacial epoch and other changes of 
climate which the geological record proves to have taken place. 
These, as enumerated by Mr. Searles V. Wood, Jun., are as 
follows : — 
1. A decrease in the original heat of our planet. 
2. Changes in the obliquity of the ecliptic. 
3. The combined effect of the precession of the equinoxes 
and of the excentricity of the earth’s orbit. 
