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 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 
