Origin of Eskers. — Crosby. 9 
He finds in Maine, where exists the finest and most extensive 
development of eskers on this continent, that while they freely 
climb slopes and cross ridges from one hundred to two hun- 
dred, and more rarely three hundred and four hundred feet 
in hight above the ground on which they rest to the north- 
ward, they are constrained to follow still deeper valleys or 
wind around still higher hills, usually seeking the lowest gap 
in a ridge or water parting. Valley eskers are very rarely 
found in the true axis of the valley or resting on the lowest 
part of the till or bed-rock profile, even where, as often hap- 
pens, the channel of the modern stream is remote from or well 
above the real bottom of the valley. But the normal position 
of the esker is lateral or along one side of the valley; and 
even the base of the esker is, not infrequently, well above, 
sometimes a hundred feet or more above, the level of the 
modern flood-plain, which may in turn overlie a great depth 
of modified drift. The indifference of eskers to the contours 
of the surfaces on which they rest is farther seen in the fact 
that they may appear first on one side of the valley, and then 
on the other, but rather rarely on both sides simultaneously; 
and the same continuous esker, broken only by the modern 
stream, may cross and recross the valley from side to side. 
Eskers seldom, if ever, occupy channels in either the bed- 
rock or till which may reasonably be regarded as due to the 
erosive action of the streams that formed the eskers. And, 
in general, distinct evidence of erosion by esker streams is 
wanting, except, perhaps, in the notching of the protruding 
drumlins or other nunataks of the waning ice-sheet. 
Eskers commonly terminate southward in the delta and over- 
wash plains formed along the southern margin of the ice-sheet, 
and to these they hold the relation of tributaries or feeders ; 
and an approximate agreement in hight of these terminal de- 
posits with the proximal portions of the eskers has often been 
noted. Also, eskers commonly widen as they approach the 
plains and merge gradually with the latter. 
Probable Status of the Ice-Sheet During the Formation 
of Eskers. 
That eskers were formed by glacial streams in, on or under 
the ice-sheet and during the waning stage of glaciation, when 
