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before crevasses extending up through the thick layers of 
yielding névé and snow to the surface could be formed ; and the 
latter condition must, of course, be realized before glacial 
moulins are a possibility. Third, that it is in the highest degree 
improbable that during the period of maximum glaciation such 
comparatively slight inequalities as the Cohasset ledges could 
have produced crevasses traversing the entire thickness of the ice- 
sheet ; just as in the case of inequalities in the bed of a river, 
the surface disturbance diminishes with the depth of the water. 
Fourth, that sinee the decay and final disappearance of the 
ice-sheet were due to a general amelioration of the climate, 
resulting in part it is probable from a depression of the land, 
it was probably aecomplished by such a general ablation of its 
upper surface as would have caused only a slight increase in 
the gradient, an increase that may have been neutralized, so 
far as its effect upon the rate of movement of the ice was con- 
cerned, by the greater depression of the land toward the north, 
and the steadily diminishing thickness, weight, and power of 
the ice. It certainly seems more reasonable to suppose that 
the rate of movement of the ice-sheet diminished as its weight 
and power declined, than that it continued to increase until the 
final disappearance of the ice. Fifth, that when the decay of 
the ice-sheet over any area was well advanced, it must have 
presented, at least during a considerable part of the year, a sur- 
face of hard, brittle ісе ; the conditions being thus more favor- 
able than at any previous period for the existence of superglacial 
streams and of crevasses traversing the entire thickness of the 
lee; and it is obvious that such crevasses are now consistent 
with a very slow movement of the ice over very slight inequal- 
ities of the ground, for the ice has lost, in its loss of weight, 
not only the power tó flow rapidly forward, but also the power 
to flow around the ledges and mold itself accurately against 
them without rupture of its mass. Sixth, that with the dimin- 
ishing thickness of the ice-sheet there must have come a time 
when it could no longer overcome the friction of so rough a 
