CHAPTER IX. 



ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE 

 ARCTIC REGIONS. 



Dr. CroU'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 evi- 

 dence — 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 Palfeozoic Epochs — Warm Arctic climates 

 in early Secondary and Palaeozoic 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 — Esti- 

 mate of the comparative effects of geographical and physical causes in 

 producing changes of climate. 



If we adopt the view set forth in the preceding chapter as to 

 the character of the glacial epoch and of the accompanying 

 alternations of climate, it must have been a very important agent 

 in producing changes in the distribution of animal and vegetable 

 life. The intervening mild periods, which almost certainly oc- 

 curred during its earlier and later phases, were sometimes more 

 equable than even our present insular climate, and severe frosts 

 were probably then unknown. During the eight or ten thousand 

 years that each such mild period lasted, some portions of the 



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