BY W. 0. CROSBY. 
1 -' 
I 
Inteoduction. 
The discussion of the origin of eskers seems to have subsided 
' almost as completely as the glacial streams by which it is universally 
conceded they ^vere formed. This is particularly true as regards the 
main question which glacialists have in recent years sought to 
determine; viz.: were subglacial or superglacial streams the princi¬ 
pal factors in the making of eskers? A large majority of geologists 
, are resting in the belief that these winding ridges of glacial gravel 
are the product chiefly, if not wholly, of the subglacial drainage of 
the ice sheet. In re-opening this discussion, as one of the still uncon¬ 
verted adherents of the superglacial theory, my main purpose is to 
. 1^ * show that under normal conditions the deposits of gravel and sand 
i ; formed in a superglacial channel may be let down upon jirma 
without obliteration and without loss of the distinctive features of 
an esker. In this connection I appeal especially to basal melting 
y: and to the principle, first enunciated by LTpham, that the ice beneath 
a superglacial river will be melted downward and the channel deep- 
I ened by the water which saturates and flows through the deposit of 
; f gravel and sand constituting the embryo esker. But I also hope to 
! " reinforce these principal arguments by others which, if less cogent 
i ^ or less vital, are yet essential to a complete theory of eskers. 
* • It is recognized by all that eskers must represent the waning stage 
t of the ice sheet; and although it is probable that the extent of basal 
melting during this stage is generally underestimated, but few will 
j ' question that it is to the surface melting or ablation of the ice that 
i ; we must look for the main source of water for the glacial streams, 
Whether superglacial or subglacial, 
: It is undoubtedly true that deposits which may be classed as 
i ^ eskers have' been formed under a variety of conditions: in super- 
’ V glacial channels, in subglacial channels, in ice-walled, earth-bottomed 
canyons, open to the sky, and with or without the active agency of 
' water. And all the theories are, no doubt, essential to a complete 
explanation of eskers, the main question now being as to their 
