Proofs of the Recent Occurrence of a Glacial Epoch—Moraines—Travelled Blocks—Glacial Deposits of Scotland: the "Till"—Inferences from the Glacial Phenomena of Scotland—Glacial Phenomena of North America—Effects of the Glacial Epoch on Animal Life—Warm and Cold Periods—Palæontological Evidence of Alternate Cold and Warm Periods—Evidence of Interglacial Warm Periods on the Continent and in North America—Migrations and Extinctions of Organisms Caused by the Glacial Epoch
CHAPTER VIII
THE CAUSES OF GLACIAL EPOCHS
Various Suggested Causes—Astronomical Causes of Changes of Climate—Difference of Temperature Caused by Varying Distances 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
CHAPTER IX
ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE ARCTIC REGIONS
Mr. Croll's Views on Ancient Glacial Epochs—Effects of Denudation in Destroying the Evidence of Remote Glacial Epochs—Rise of Sea-level Connected with Glacial Epochs a Cause of Further Denudation—What Evidence of Early Glacial Epochs may be Expected—Evidences of Ice-action During the Tertiary Period—The Weight of the Negative Evidence—Temperate Climates in the Arctic Regions—The Miocene Arctic Flora—Mild Arctic Climates of the Cretaceous Period—Stratigraphical Evidence of Long-continued Mild Arctic Conditions—The Causes of Mild Arctic Climates—Geographical Conditions Favouring Mild Northern Climates in Tertiary Times—The Indian Ocean as a Source of Heat in Tertiary Times—Condition of North America During the Tertiary Period—Effect of High Excentricity on Warm Polar Climates—Evidences as to Climate in the Secondary and Palæozoic Epochs—Warm Arctic Climates in Early Secondary and Palæozoic Times—Conclusions as to the Climates of Secondary and Tertiary Periods—General View of Geological Climates as Dependent on the Physical Features of the Earth's Surface—Estimate of the Comparative Effects of Geographical and Physical Causes in Producing Changes of Climate.