184 



ISLAND LIFE. 



[part I. 



penetrates within the Arctic circle, is through Behring's Straits ; 

 but this is both shallow and limited in width, and the con- 

 sequence is that the larger part of the warm currents of the 

 Pacific turns back along the shores of the Aleutian Islands and 

 North-west America, while a very small quantity enters the 

 icy ocean. 



But if there were other and wider openings into the Arctic 

 Ocean, a vast quantity of the heated water which is now turned 

 backward would enter it, and would produce an amelioration 

 of the climate of which we can hardly form a conception. A 

 great amelioration of climate would also be caused by the 

 breaking up or the lowering of such 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 pre- 

 vails. It is, no doubt, difficult and often impossible to deter- 

 mine 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 CliwMes 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 



