When the Greenland section is included, the Canadian Shield is approximately circular, bounded on the northeast by the northeast edge of Greenland, with Hudson Bay in the middle. The northeastern portion, however, became tilted up so that, in northern Labrador and Baffin Island, the land rises to more than 1,500 metres (5,000 feet) above sea level. During the Pleistocene Epoch, continental ice sheets depressed the land surface (creating Hudson Bay) but also tilted up its northeastern "rim" (the Torngat), scooped out thousands of lake basins, and carried away much of the region's soil. Today it consists largely of an area of low relief 300–610 m (980–2,000 ft) above sea level with a few monadnocks and low mountain ranges (including the Laurentian Mountains) probably eroded from the plateau during the Cenozoic Era.
The metamorphic base rocks are mostly from the Precambrian (between 4.5 billion and 540 million years ago) and have been repeatedly uplifted and eroded. It is the Earth's greatest area of exposed Archean rock. The Canadian Shield was the first part of North America to be permanently elevated above sea level and has remained almost wholly untouched by successive encroachments of the sea upon the continent. The Canadian Shield is a collage of Archean plates and accreted juvenile arc terranes and sedimentary basins of the Proterozoic Eon that were progressively amalgamated during the interval 2.45–1.24 Ga, with the most substantial growth period occurring during the Trans-Hudson orogeny, between c. The Canadian Shield once had jagged peaks, higher than any of today's mountains, but millions of years of erosion have changed these mountains to rolling hills. The age of the Canadian Shield is estimated to be 4.28 Ga. The Canadian Shield is a U-shaped subsection of the Laurentia craton signifying the area of greatest glacial impact (scraping down to bare rock) creating the thin soils. The shield extends into the United States as the Adirondack Mountains (connected by the Frontenac Axis) and the Superior Upland. The Canadian Shield is a physiographic division comprising four smaller physiographic provinces: the Laurentian Upland, Kazan Region, Davis and James. As a deep, common, joined bedrock region in eastern and central Canada, the Shield stretches north from the Great Lakes to the Arctic Ocean, covering over half of Canada and most of Greenland it also extends south into the northern reaches of the United States. Glaciation has left the area with only a thin layer of soil, through which exposures of igneous bedrock resulting from its long volcanic history are frequently visible. It forms the North American Craton (or Laurentia), the ancient geologic core of the North American continent. The Canadian Shield ( French: Bouclier canadien ), also called the Laurentian Plateau, is a geologic shield, a large area of exposed Precambrian igneous and high-grade metamorphic rocks.
It spans eastern, northeastern, and east-central Canada and the upper midwestern United States. The Canadian Shield is a broad region of Precambrian rock (pictured in shades of red) that encircles Hudson Bay.
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