principal glacial cover of North America during the Pleistocene Epoch (1,600,000 to 10,000 years ago). At its maximum extent it spread as far south as latitude 37° N and covered an area of more than 13,000,000 square km (5,000,000 square miles). In some areas its thickness reached 2,400–3,000 m (8,000–10,000 feet) or more. The Laurentide Ice Sheet probably originated on the Labrador-Ungava plateau and on the mountains of the Arctic islands of Canada, and centred over Hudson Bay. As it spread, the glacial ice mass appears to have combined with other ice caps that had formed on local highlands in eastern Canada and in the northeastern United States.