552 FORMER EXISTENCE OF LOCAL GLACIERS 
A few flatter fragments with more angular outlines show only 
one kind of scratches, having evidently been held for a 
longer time in the same position. This drift, however it may 
vary in its mineralogical components in different localities, 
exhibits everywhere the same characteristic treatment over 
the whole country, from the shores of the Atlantic to the 
Rocky Mountains and beyond. In the White Mountain re- 
gion it has the same mineralogical character north and south 
of the range, and rests everywhere upon the well known 
roches moutonnées, in one word, upon the planed, grooved, 
polished and scratched surfaces of the rocks underlying it. 
Observation has taught us that materials such as those de- 
scribed above, so combined, exhibiting the same characters 
in their surfaces and having the same diversity.of composi- 
tion and absence of all sorting or regular arrangement, occur 
now at the bottom of the great glaciers of our time, and 
nowhere else; being found between the ice and the rocks 
over which it moves,—the result in fact of the grinding 
action of advancing glaciers. On account of their unvarying 
position I have called these deposits “ground moraines,” 
because they are always resting upon the rocky floor of the 
country, between it and the under surface of the ice. Our 
typical unaltered so-called northern drift is synonymous 
with. the ground moraines of the present day, differing only 
in its greater extension. It is in fact a ground moraine 
spreading over the greatest part of the continent. All its 
characteristics, identical in every detail with those of the. 
deposits underlying the present glaeiers, show that it can 
only have been formed under a moving body of ice, held 
between it and the underlying mass of rock. The great 
ice sheet of the glacial period which fashioned the drift 
must therefore have been co-extensive with the distribution 
of the latter. It is very important to distinguish this drift 
from the moraines formed under other circumstances, and 
from the so-called erraties and perched blocks. Moraines, 
as commonly understood, that is, lateral and frontal mo- 
