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 Sierra Nevada to south of San Francisco, the mountain centres developed local glaciers, which in some places were of very great size, perhaps exceeding any of those which now exist in Switzerland. It will thus be seen that nearly one half of the present land area of North America was beneath a glacial covering, though, as before noted, the region about the Gulf of Mexico may have swayed upward when the northern portion of the land was borne down by the vast load of ice which rested upon it. Notwithstanding this possible addition to the land, our imaginary explorer would have found the portion of the continent fit for the occupancy of life not more than half as great as it is at present.