iliar with the facts could suppose that floating
ice or icebergs had abraded, polished, and furrowed the bottom of narrow
valleys as we find them worn, polished, and grooved by glaciers. And it
must be remembered that this is a theory founded not upon hypothesis,
but upon the closest comparison. I have not become acquainted with these
marks in regions where glaciers no longer exist, and made a theory to
explain their presence. I have, on the contrary, studied them where they
are in process of formation. I have seen the glacier engrave its lines,
plough its grooves and furrows in the solid rock, and polish the
surfaces over which it moved, and was familiar with all this when I
found afterwards appearances corresponding exactly to those which I had
investigated in the home of the present glaciers. I could therefore say,
and I think with some reason, that "this also is the work of the glacier
acting in ancient times as it now acts in Switzerland."

There is another character of glacial action distinguishing it from any
abrasions caused by water, even if freighted with a large amount of
loose materials. On any surface over which water flows we shall find
that the softer materials have yielded first and most completely. Hard
dikes will be left standing out, while softer rocks around them are worn
away,--furrows will be eaten into more deeply,--fissures will be
widened,--clay-slates will be wasted,--while hard sandstone or limestone
and granite will show greater resistance. Not so with surfaces over
which the levelling plough of the glacier has passed. Wherever softer
and harder rocks alternate, they are brought to one outline; where dikes
intersect softer rock, they are cut to one level with it; where rents or
fissures traverse the rock, they do not seem to have been widened or
scooped out more deeply, but their edges are simply abraded on one line
with the adjoining surfaces. Whatever be the inequality in the hardness
of the materials of which the rock consists, even in the case of
pudding-stone, the surface is abraded so evenly as to leave the
impression that a rigid rasp has moved over all the undulations of the
land, advancing in one and the same direction and levelling all before
it.

Among the inequalities of the glacier-worn surfaces which deserve
especial notice, are the so-called "_roches moutonnees_." They are
knolls of a peculiar appearance, frequent in the Alps, and first noticed
by the illustrious De Saussure,