Origin of Eskers. — Crosby. 31 
hanging valleys, in which the aggrading will necessarily be 
unimportant. Stone says,* in this connection, "From what- 
ever point of view we look, the difficulties are immense in 
accounting for the branchings of the rivers of the ice-sheet, 
their directions and their relations to the relief forms of the 
land, the nature of their sediments, etc., on the theory that we 
are dealing with subglacial streams alone." 
Double and Reticulated Eskers. — That the superglacial 
deposits afford, in the case where the bordering ice disappears 
before the underlying ice, a complete and satisfactory explan- 
ation of the double eskers has been noted ; while as subglacial 
deposits they are essentially inexplicable, whether the adja- 
cent and parallel tunnels which must be postulated are regard- 
ed as contemporaneous or successive in their formation and ag- 
grading. Similarly, the reticulated eskers and kames are most 
easily explained as superglacial deposits, representing the 
delta-like branching of the superglacial stream at points where 
it was approximately base-levelled and the surface of the bor- 
dering ice had been reduced nearly to its level by general abla- 
tion. Another explanation would be that the deposit formed 
in a lake-like expansion of the river was split up into a net- 
work of ridges through the unequal melting of the subjacent 
ice, while it was being let down upon the ground. It is an es- 
sential part of the superglacial hypothesis that while, through 
subflavial and basal melting, the more or less perfectly aggrad- 
ed deposits may be let down on terra firiiia without being se- 
riously disordered, exceptions must occur of such character 
and frequency as, apparently, to explain every aberrant phase 
of esker formation. 
Stone showsf that the reticulated eskers, like the broad 
eskers and esker terraces, are most readily and satisfactorily 
explained by supposing that the subglacial streams became 
locally, at least, superglacial. Again, he saysj that ^subglacial 
streams crossing hills and ridges are inconsistent with the ex- 
istence of crevasses which might divert the water, which 
"bides its time and at the first eligible transverse crevasse 
steals off sidewise toward the lower ground." Also, that in the 
* V. S. G. S , Mon. 34, p. 324. 
t V. S. G. S.. Mon 34, p. 465. 
tlhid., p. 299. 
