This is important to remember, because, when we
examine the drift in countries where the ice, during the glacier-period,
overtopped nearly all the mountains, so that few fragments could fall
from them upon its surface, we find scarcely any angular boulders, while
the drift is interspersed with larger fragments of this character,
carried under the ice, instead of on its back. Another distinction
between water-worn deposits and drift consists in the fact that the
former are washed clean, while the latter always retains the mud
gathered during its journey and spread throughout its mass.
In summing up the glacial evidences, I must not omit the moraines,
though I have described them so fully in a previous article that I need
not do more than allude to them here; but any argument for the glacial
theory which did not include these characteristic walls erected by
glaciers would be most imperfect. We need hardly discuss the theory of
currents with reference to the formation of terminal moraines, extending
across the valleys from side to side. Any current powerful enough to
bring the boulders and _debris_ of all sorts of which these walls are
composed to the places where they are found would certainly not build
them up with such regularity, but would sweep them away or scatter them
along the bottom of the valley.
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