CHAP. IX MILD ARCTIC CLIMATES 191 



Arctic highlands as now favour the accumulation of ice ; 

 while the interpenetration of the sea into any part of the 

 great continents in the tropical or temperate zones would 

 again tend to raise the winter temperature, and render any- 

 long continuance of snow in their vicinity almost 

 impossible. 



Now geologists have proved, quite independently of any 

 such questions as we are here discussing, that changes of 

 the very kinds above referred to have occurred during the 

 Tertiary period ; and that there has been, speaking broadly, 

 a steady change from a comparatively fragmentary and 

 insular condition of the great north temperate lands in 

 early Tertiary times, to that more compact and continental 

 condition which now prevails. It is, no doubt, difficult and 

 often impossible to determine how long any particular 

 geographical condition lasted, or whether the changes in 

 one country were exactly coincident with those in another ; 

 but it will be sufficient for our purpose briefly to indicate 

 those more important changes of land and sea during the 

 Tertiary period, which must have produced a decided 

 effect on the climate of the northern hemisphere. 



Geographical Changes Favouring Mild Northern Climates 

 in Tertiary Times, — The distribution of the Eocene and 

 Miocene formations shows, that during a considerable 

 portion of the Tertiary period, an inland sea, more or less 

 occupied by an archipelago of islands, extended across 

 Central Europe between the Baltic and the Black and 

 Caspian Seas, and thence by narrower channels south- 

 eastward to the valley of the Euphrates and the Persian 

 Gulf, thus opening a communication between the North 

 Atlantic and the Indian Oceans. From the Caspian also a 

 wide arm of the sea extended during some part of the 

 Tertiary epoch northwards to the Arctic Ocean, and there 

 is nothing to show that this sea may not have been in 

 existence during the whole Tertiary period. Another 

 channel probably existed over Egypt ^ into the eastern 



^ Mr. S. B. J. Skertchley informs me that he has himself observed thick 

 Tertiary deposits, consisting of clays and anhydrous gypsum, at Berenice 

 on the borders of Egypt and Nubia, at a height of about 600 feet above the 

 sea-level ; but these may have been of fresh-water origin. 



