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 Palaeozoic Epochs — Warm Arctic Climates 

 in Early Secondary and Palaeozoic Times — Conclusions as to the Climates 

 of Secondary and Tertiarj^ 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 Pro- 

 ducing 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 accom- 

 panying 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 occurred during its earlier 

 and later phases, may have been sometimes more equable 

 than even our present insular climate, and severe frosts 

 were probably then unknown. During the four or five 



