While the study of glaciers began in Europe, inquiries concerning
their ancient extension have been carried further and with more
accuracy in North America than in any other part of the world. We may
therefore well begin our description of the limits of the ice sheets
with this continent. Imagining a seafarer to have approached America
by the North Atlantic, as did the Scandinavians, and that his voyage
came perhaps a hundred thousand years or more before that of Leif
Ericsson, he would have found an ice front long before he attained the
present shores of the land. This front may have extended from south of
Greenland, off the shores of the present Grand Banks of Newfoundland,
thence and westward to central or southern New Jersey. This cliff of
ice was formed by a sheet which lay on the bottom of the sea. On the
New Jersey coast the ice wall left the sea and entered on the body of
the continent. We will now suppose that the explorer, animated with
the valiant scientific spirit which leads the men of our day to seek
the poles, undertook a land journey along the ice front across the
continent. From the New Jersey coast the traveller would have passed
through central Pennsylvania, where, although there probably detached
outlying glaciers lying to the southward as far as central Virginia,
the main front extended westward into the Ohio Valley. In southern
Ohio a tongue of the ice projected southwardly until it crossed the
Ohio River, where Cincinnati now lies, extending a few miles to the
southward of the stream. Thence it deflected northwardly, crossing the
Mississippi, and again the Missouri, with a tongue or lobe which went
far southward in that State. Then again turning to the northwest, it
followed in general the northern part of the Missouri basin until it
came to within sight of the Rocky Mountains. There the ice front of
the main glacier followed the trend of the mountains at some distance
from their face for an unknown extent to the northward. In the
Cordilleras, as far south as southern Colorado, and probably in the