Perry.] 120 | [February 28, 
doubt, the movement northward was more rapid, in others less so, 
the ice in many spots, it may be for long years, seeming to be almost 
at a stand-still. Occasionally, perhaps, it advanced in places for a 
season, only afterward to.retreat; again, after a while, it moved for- 
ward, once more in due time to recede, and finally to disappear from 
a given level altogether. Amidst these various changes, of course, 
the wasting border would be very irregular; owing to such mutations 
in broken regions, it might be extremely rugged and ragged ; very 
similar, most likely, to an uneven and deeply-indented sea-coast, on 
which the ocean is making ceaseless inroads. 
Associated with the steadily advancing waste of the ice-mass are 
two results which claim brief attention in connection with the other 
phenomena of the Glacial period. ‘They should be particularly no- 
ticed since they relate to the deposits specially characteristic of the 
times, and serve to draw a sharp line of distinction between them. 
The first pertains to the drift connected with the main ice-sheet. The 
ice beginning to thaw, the detrital matter, which lay beneath it and 
is now frequently called typical drift, was uncovered on its southern 
limits, and in many places left substantially as we now find it. As 
the melting went on, and the wintry mass retreated, there would be 
more and more laid bare, and thus brought to light, the great under- 
lying blanket of heterogeneous and unstratified detritus, which had 
been forming and taking its place all through the great winter of 
ages. It probably prevailed nearly everywhere beneath the main ice- 
mass, and is now found spread in one almost unbroken sheet over the 
country. This properly constitutes the lower or glaciated drift, which 
I have described as a sort of disguised moraine. It is a vast morainic 
sheet of glaciated matter, having to a large extent a uniform charac- 
ter all over an immense region, thé materials, though of local origin 
and thus differing mineralogically according to localities, yet exhibit- 
ing substantially the same general characteristics, indicative of the 
widely extended action of ice under one all-prevailing set of con- 
ditions. Hence it should be unmistakably clear that Arctic icebergs 
could not have furnished the material of New England typical drift, 
since the latter was for the most part derived from the neighborhoods 
in which it is now found; while bergs of ice from the White Moun- 
tains could not have supplied it, for it is a continuous sheet, having a 
uniform glaciated character, spreading over vast areas lying far to the 
north as well as extending to the south of these mountains. So, 
again, on the wasting of the great ice-sheet, whatever of material it 
