One of the world's largest geologic continental shield s, centred on Hudson Bay and extending for 3 million sq mi (8 million sq km) over Canada from the Great Lakes to the Canadian Arctic and into Greenland, with small extensions into northern Minnesota, Wisconsin, Michigan, and New York.
It is the largest mass of exposed Precambrian rock on earth. The region as a whole is composed of ancient crystalline rocks whose complex structure attests to a long history of uplift and depression, mountain building, and erosion.