i6 Tlic American Geologist. •'"^^'j- ^^^^• 
mountains, with a steep frontal slope, and feeling the thrust of 
powerful alpine glaciers, can become absolutely stagnant in a 
distance of only five to fifteen miles from the mountains, and 
while still retaining a thickness of a thousand feet or more, we 
need not doubt that the wasted margins of the Pleistocene ice- 
sheet, on the vast, dissected, peneplain tracts of extremely low 
gradient and scores and hundreds of miles from the nearest 
mountains and these never more than one-third as lofty as 
the St. Elias range, also became stagnant across a marginal 
zone of considerable breadth. This point of view seems to de- 
mand not only great thickness of the continental ice-sheet in 
its prime or before it ceased to move, but also overriding alike 
of the immature and of the old and washed margin as a means 
of inducing and renewing motion in the latter, and this over- 
riding must involve the transfer of englacial drift in great 
volumes to higher levels in the ice than many glacialists have 
heretofore been willing' to accept. 
Glacial potholes, it may be noted farther, are, in general, 
far more likely to be the products of subglacial streams than 
of moulins, for they lack the elongation which the latter ex- 
planation requires ; and the subglacial stream may or may not 
have originated in a moiilin. The assumption that it did is by 
no means necessary. That the glacial potholes were in general 
formed after the ice became absolutely and finally stagnant, 
must be obvious to anyone who has studied them in the field 
and noted the perfectly normal and unglaciated condition of 
their rims. 
To summarize, it appears probable that eskers were formed 
in connection with the sluggish or wholly stagnant, marginal 
portion of the waning ice-sheet, after the liberation by basal 
melting of all that part of the ground moraine, including drum- 
lins, showing evidence of having been pressed down and com- 
pacted by the movement as well as by the dead weight of 
the ice ; and after the upper part of the englacial drift had 
become superglacial through the superficial melting or ablation 
of the ice. Such crevasses as may have survived the cessation 
of flow, or resulted from local subsidence due to basal melting, 
were probably closed by drift washed into them from above. 
The general absence of modified drift interstratified with the 
till i'S an indication that subglacial streams or a concentrated 
