MESOZOIC AND CENOZOIC GEOGRAPHY 487 
rapid rate. The climate there is even now in process 
of change. What its outcome will be no one can tell; 
but surely at the present time the climate of the 
northern hemisphere shows signs of increasing moder- 
ateness. Possibly then, the time may come when, as 
in the Tertiary period, life can extend its zone of 
occupation further and further north following in the 
wake of the retreating ice sheets. 
The Glacial period has produced effects of the 
utmost importance to man. The ice has occupied a 
large part of the world in which the later history of 
mankind has been enacted. Northwestern Europe and 
northeastern America are the seats of two important 
civilizations, and the changes caused by the ice, and 
accompanying it, have been among the most notable 
of the influences upon which the development has 
taken place. The very soil that he tills, the har- 
bors of the coasts, the water power of the rivers, 
and much of the scenery of the land, have resulted 
from the conditions accompanying ice occupation and 
withdrawal. Man is dependent upon the earth, and 
everywhere we see close relation between his prog- 
ress and the geological conditions; but in no instance 
is this more strikingly shown than in the case of that 
latest great change, the Glacial period. 
