lopes of mountain valleys, so
does a study of the same class of facts in South America reveal new and
unlooked-for features in the history of the ice period. Some will say,
that the fact of the advance of ice-fields over an open country is by no
means established, inasmuch as many geologists believe all the so-called
glacial traces, viz. striae, furrows, polish, etc., found in the United
States, to have been made by floating icebergs at a time when the
continent was submerged. To this I can only answer, that in the State of
Maine I have followed, compass in hand, the same set of furrows, running
from north to south in one unvarying line, over a surface of one hundred
and thirty miles from the Katahdin Iron Range to the sea-shore. These
furrows follow all the inequalities of the country, ascending ranges of
hills varying from twelve to fifteen hundred feet in height, and
descending into the intervening valleys only two or three hundred feet
above the sea, or sometimes even on a level with it. I take it to be
impossible that a floating mass of ice should travel onward in one
rectilinear direction, turning neither to the right nor to the left, for
such a distance. Equally impossible would it be for a detached mass of
ice, swimming on the surface of the water, or even with its base sunk
considerably below it, to furrow in a straight line the summits and
sides of the hills, and the beds of the valleys. It would be carried
over the depressions without touching bottom. Instead of ascending the
mountains, it would remain stranded against any elevation which rose
greatly above its own basis, and, if caught between two parallel ridges,
would float up and down between them. Moreover, the action of solid,
unbroken ice, moving over the ground in immediate contact with it, is so
different from that of floating ice-rafts or icebergs, that, though the
latter have unquestionably dropped erratic boulders, and made furrows
and striae on the surface where they happened to be grounded, these
phenomena will easily be distinguished from the more connected traces of
glaciers, or extensive sheets of ice, resting directly upon the face of
the country and advancing over it.

There seems thus far to be an inextricable confusion, in the ideas of
many geologists, as to the respective action of currents, icebergs, and
glaciers. It is time they should learn to distinguish between classes of
facts so different from each other, and so easily recognized a