932 THE JOURNAL OF GEOLOGY. 
RELATION OF THE CURRENTS TO THE SUBGLACIAL TOPOGRAPHY. 
It seems from the above to be fairly well proven that differ- 
ential currents, vertical and horizontal, do exist in the bottom 
portion of the ice, and recognizing their existence it is possible 
to attempt the explanation of certain features of subglacial 
topography. It can be shown that great drumlin-covered drift 
deposits lie in the lee of escarpments, or other irregularities of 
the surface, composed of hard rocks, over which the ice has just 
passed. 
The upward currents produced at the front of an escarpment 
and extending over it in an arch have already been pointed out. 
The active portion of the ice bottom is undoubtedly in the region 
of the descending currents and the portion below the arch must 
be one of very slight activity. Inspeaking of drumlins Professor 
Chamberlin mentions this curve and says, p. 216: ‘‘I suspect that 
this is the true drumlinoid curve and that it represents the balance 
or the accommodation between the force of the overthrust of the 
over-riding ice on the one side and the friction and resistance of 
the ice and débris against the embossment on the other. I sus- 
pect that the progressive tendency in such a case is toward the 
accumulation of débris below the drumlinoid line, which was 
apparently a line of shearing, and that the result of such an 
accumulation would be a drumlin.” 
This idea was also entertained by the author and applied to 
the formation not only of drumlins but to the larger deposits of 
drift. It will be easily seen that in passing large escarpments the 
base of the proportionally large arch currents would be thrown 
into minor arching currents by minor irregularities on the escarp- 
ment. The large arches would have under them regions of rela- 
tively smaller ice motion with consequent deposition of débris ; 
the point of descent of the current would determine regions of 
erosion. This action will be clearly seen by reference to the 
diagram, Fig. 11. A line was taken from Sodus Bay on Lake 
‘Ontario to a few miles south of Ithaca, N. Y., taking in the deep- 
est part of Cayuga Lake. Upon this line is projected the 
extremes of elevation in surface a few miles to each side of it. 
