Drift of the North German Lowland.—NSalishury. 309 
‘basins is, so far as the United States is concerned, much less gen- 
‘eral than Dr. Wahnschaffe seems to imply. While it is true that 
our terminal moraines surround lakes Erie, Michigan and Superior, 
it is also true that similar moraines frequently stand in no definite 
relation to well defined basins. The moraine loop which runs down 
into central Iowa, is not associated with any well-defined basin. 
‘The moraine crossing New Jersey and eastern Pennsylvania is al- 
together independent of any basin, and if such drift ridges are 
sometimes developed independently of basins, they cannot be said 
to be dependent upon them. The depressions were of course in- 
fluential in determining the course of ice movement, and so in de- 
termining the position and form of the ice’s edge, and it is the 
accumulation of drift made beneath the ice’s edge while it was 
‘stationary or oscillating, which constitutes, according to American 
usage, the main part of the terminal moraine. 
The conception of American geologists concerning the origin 
of the terminal moraines (‘‘ ground moraine landscape” ), is not 
very different from the view of Dr. Keilhack concerning the origin 
of the Baltic ridge. It is believed that beneath various parts of 
the ice’s edge, varying amounts of glacial debris accumulated dur- 
ing any given period of time. ‘This in itself, would give rise to a 
ssubmarginal ridge of unequal hight and width, wherever the edge 
of the ice remained constant in position for any considerable 
period. Every minor retreat of the ice may have been accompanied 
by changes in the details of the form of its edge, and as the mar- 
gin of the ice changed both in position and in form, new accumu- 
lations of drift would be made beneath it, comparable to the first. 
When the ice re-advanced, never so little, its form might be again 
changed, and the submarginal accumulations would be made in a 
new position and in a new form. Thus it is conceived that by re- 
peated retreats and advances within narrow limits,and by repeated 
alterations in the form of the ice-margin with or without general 
oscillations, the terminal moraine material was accumulated. The 
first condition for the development of a terminal moraine there- 
fore, is a stationary ice margin, or a margin which oscillates 
backward and forward within narrow limits, while the details of its 
form are continually changing. The extent of these oscillations 
will be one of the considerations determining the width of the mo- 
rainic belt. The waters issuing from the edge of the ice, which was 
always melting, often worked considerable changes upon the ma- 
