ches moutonnees_, trending in a continuous ridge from east to west,
over which the masses of northern ice have moved unimpeded to the
latitude of the Ohio.

Owing to the absence of high mountain-ranges over this vast expanse of
land, the glacial phenomena of America are not grouped about special
centres of dispersion, or radiating from them, as in Europe. During the
greatest extension of the ice-fields, there were but few prominent peaks
rising above them, and dropping here and there huge boulders on their
surface, to be transported to great distances without losing their rough
angular character. And when the temperature under which these vast
frozen masses had been formed rose again, the wasting ice must have
yielded first on its southern boundary, gradually and uniformly
retreating to the Arctic regions, without breaking up into distinct
glacial regions, separated from one another, each with its local
distribution of erratic boulders and glacier-marks radiating from
circumscribed areas on higher levels, as they occur everywhere in
Europe. It is true that there are a few localities within the Alleghany
range, on the Green and White Mountains, and in parts of Maine, where it
is evident that local glaciers have had a temporary existence; but even
throughout this eastern coast-range the elevation of the mountains is so
slight, and their trend so uniform in a northeasterly and southwesterly
direction through twenty degrees of latitude, that the localization of
the phenomena is less marked than in Norway, Great Britain, or
Switzerland. In short, the ice of the great glacial period in America
moved over the continent as one continuous sheet, overriding nearly all
the inequalities of the surface. Thus the peculiar physical character of
the country gives a new aspect to the study of glacial evidences here.
The polished surfaces stretch continuously over hundreds and hundreds of
miles; the rectilinear scratches, grooves, and furrows are unbroken for
great distances; the drift spreads in one vast sheet over the whole
land, consisting of an indiscriminate medley of clays, sands, gravels,
pebbles, boulders of all dimensions, and so uniformly mixed together
that it presents hardly any difference in its composition, whether we
examine it in New England, New York, Pennsylvania, Ohio, Michigan,
Indiana, Illinois, Wisconsin, in Iowa beyond the Mississippi, in the
more northern Territories, or in Canada.

In Europe, boulders of large d