92 
ICE-PERIOD IN AMERICA. 
admit the possibility of the former existence 
of glaciers over such a wide, unbroken expanse 
of level land. This backwardness is, no doubt, 
partly due to the fact, that, as glaciers have 
hitherto been studied in mountainous coun¬ 
tries, their presence has been supposed to im¬ 
ply the presence of mountains, this impression 
being strengthened by the downward and on¬ 
ward movement of existing glaciers, so long 
supposed to be exclusively due to the slopes 
along which all modern glaciers advance. Were 
it true that glaciers move solely or mainly on 
account of the sloping bottom on which they 
rest, and that they can advance only on an 
inclined plane, all the phenomena concerning 
drift, polished and furrowed surfaces, boul¬ 
ders, etc., in America, would hardly justify us 
in assuming a moving sheet of ice as their 
cause. But we have seen that the phenomena 
of glaciers, like those of currents, are in great 
part meteorological. The Gulf Stream does 
not flow toward the English shore because the 
ocean-bottom slopes eastward; nor does the 
cold current of Baffin’s Bay run down hill 
when it pours its icy waters southward upon 
our northeast coast. Their course is deter- 
