86 
ICE-PERIOD IN AMERICA. 
path of the ice. Even pebbles imbedded in 
masses of pudding-stone, but rising sometimes 
above the level of the general surface, often 
have their northern side polished and scratched, 
while the southern one remains untouched. 
Moraines are not wanting to complete the 
chain of evidence respecting the ancient exist¬ 
ence of glaciers in this country, although we 
cannot expect to find them here so frequently 
as in Europe, where the many local glaciers in 
circumscribed valleys afforded special facilities 
for the building up of these lateral and trans¬ 
verse walls. Over the broad expanse of the 
United States, on the contrary, with such 
slight variations of level, the disappearance of 
the ice at its breaking-up would naturally be 
more complete and continuous than in a coun¬ 
try intersected by frequent mountain-chains, 
where the ice would linger in the higher val¬ 
leys long after it had disappeared from the 
plains below. Yet it is evident that here also 
in certain localities the boundary line of the 
ice underwent oscillations, pausing here and 
there long enough to collect mounds of the 
same character as those spanning the valleys 
of Switzerland and Great Britain. We have 
