4*79 
[DaviS. 
.S92.] 
to transportation up-hill, as in the formation of dunes or in the 
wider distribution of dust by means of whirlwinds. 
On the other hand, in a climate characterized by cold and by 
a sufficient precipitation of snow for the production of extended 
ice-sheets, the waste of the land is again distributed in a peculiar 
way over the surface on its way to the sea. Although hidden 
from observation while the ice-sheet is present, these peculiar 
forms of land waste become very noticeable when climatic change 
melts the ice-sheet away and discloses the surface over which it 
was creeping. In this case the local accumulation of land waste 
in specialized topographic forms appears to result chiefly from 
the application of the glacial forces all over the land surfaces, so 
that the waste is not concentrated along the narrow drainage 
lines characteristic of transportation by water, but is dragged or 
carried or washed broadly across the country. As before, the 
accumulated waste frequently conceals the topographic forms pro- 
duced before the advent of the special climate under considera- 
tion; and curiously enough, some of the forms of accumulation 
again involve at least a local transportation up-hill, as in drum- 
lins or in a smaller way in the scattered boulders that are left at 
a higher level than their sources. 
It is important to notice that the climatic oscillations from 
warm to cold or from moist to dry are relatively rapid, occurring 
within a brief part of an entire geographical cycle or period of 
time during which a land mass is worn down from its early con- 
structional forms to the base-leveled monotony of old age. 
The forms assumed by the waste of the land on its way to the 
sea in an arid climate are for the most part remarkably simple 
and regular. The waste has a steeper slope of coarser material 
near its source of supply on the mountain sides, then a gentler 
slope lying at less and less angle of descent, until in the middle 
of enclosed basins or near the sea at a distance from the moun- 
tain foot, the surface becomes almost level. The forms accumu- 
lated under and at the margin of ice-sheets in a cold climate 
are, on the other hand, extremely varied, and it is to one of these 
that this essay is devoted. I do not propose to discuss here the 
evidence of glacial action. The conclusion that New England 
with a large part of northeastern North America was not long ago 
invaded by an ice-sheet is accepted as well demonstrated, and at- 
tention is given only to a special product of its action. 
