CONTENTS. 



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 — Per- 

 petual snow nowhere exists on lowlands — Conditions determining the presence or 

 absence of perpetual Snow — Efficiency of Astronomical causes in producing Glaci- 

 ation — 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 aiilielion 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 



Facje^ 121—162 



CHAPTER IX. 



ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE ARCTIC EEGIONS. 



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 Cretacious Period— Strati- 

 graphical evidence of long-continued mild Arctic conditions — The causes of mild 

 Arctic climates — Geographical conditions favouring mild northern climates in Ter- 

 tiary times — The Indian Ocean as a source of heat in Tertiary times — Condi- 

 tion of North America during the Tertiary Period — Effect of high excentricity on 

 warm Polar climates — Evidences as to climate in the Secondary and Palaeozoic 

 Epochs — "Warm Arctic climates in early Secondary and Palaeozoic times — Con- 

 clusions 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 Pages 163 — 202 



CHAPTER X. 



THE earth's AGE, AND THE RATE OF DEVELOPMENT OF ANIMALS AND PLANTS. 



Various estimates of Geological Time — Denudation and deposition of Strata as a 

 measure of Time — How to estimate the thickness of the Sedimentary Rocks — 

 How to estimate the average rate of deposition of the Sedimentary Rocks — The 

 rate of Geological change probably greater in very remote times — Value of the 

 preceding estimate of Geological Time — Organic modification dependent on 

 Change of Conditions — Geographical mutations as a motive power in bringing 

 about Organic Changes — Climatal revolutions as an agent in producing Organic 

 Changes — Present condition of the Earth one of exceptional stability as regards 

 Climate— Date of last Glacial Epoch and its bearing on the Measurement of 

 Geological time — Concluding Remarks . t . . . Fages 203—229 



