II.

Geology

The oldest part of the North American crustal plate, its rocks contain fossils of some of the earliest forms of life, such as algae and bacteria from more than 2 billion years ago. During the most recent of the Ice Ages, beginning about 2.5 million years ago, continental ice sheets covered the region, stripping away soil, depositing glacial drift, and creating many lake basins and riverbeds. Present-day elevations in the shield are mostly between 300 and 600 m (984 and 1,969 ft) above sea level, except in limited areas, such as the Quebec-Labrador Peninsula, where they rise to about 1,070 m (3,510 ft). Where the shield has been tilted upwards, elevations are greatest—Mount Thule on Baffin Island reaches a height of 1,711 m (5,614 ft), while the highest point in the Torngat Mountains of Labrador is 1,652 m (5,420 ft).