ts 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. That this is actually the case is seen
in the lower course of the valley of the Rhone, where there are no
transverse moraines, while they are frequent and undisturbed in the
upper part of the valley. This is no doubt owing to the fact, that, when
the main glacier had already retreated considerably up the valley, the
lateral glaciers from the chains of the Combin and the Diablerets still
reached the valley of the Rhone at a lower point, and barred the outlet
of the waters from the glaciers above. A lake was thus formed, which,
when the lower glaciers retreated up the lateral valleys, swept away all
the lower transverse moraines, and formed the flat bottom of Martigny.
In this case, the moraines were totally obliterated; but there are many
other instances in which the materials have been only broken up and
scattered over a wider surface by currents. In such remodelled moraines,
the glacier-mud has, of course, been more or less washed away. We have
here a blending of the action of water with that of the glacier; and,
indeed, how could it be otherwise, when the colossal glaciers of past
ages gradually disappeared or retreated to the mountain-heights? The
wasting ice must have occasioned immense freshets, the action of which
we shall trace hereafter, when examining the formation of our
drift-ponds, of our river-beds and estuaries, as well as the
river-terraces standing far above the present water-level.

And now, if it be asked how much of this evidence for the former
existence of glaciers is to be found in Great Britain, I answer, that
t