CHAPTER IX. 
ANCIENT GLACIAL EPOCHS, AND MILD CLIMATES IN THE 
ARCTIC REGIONS. 
Dr. 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 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 Paleozoic 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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