Shield

The Precambrian Shield is an extensive structural unit of the Earth's crust composed of exposed basement rocks formed during the Archean or Proterozoic eons which together comprise the Precambrian Era ending 544 million years ago. Originally formed during several rounds of mountain-building activity, Shield rocks are now among the most stable on Earth. The Precambrian mountain belts have since eroded away, creating the low, rolling rock plain we see today. The best-known examples are the Canadian Shield and the Baltic Shield in Scandinavia.

Keywords

Landforms

Canadian Shield

The Canadian Shield covers about 4.8 million km². North to south it extends from the ARCTIC ARCHIPELAGO to the states of Wisconsin and New York; east to west from Labrador to the western Northwest Territories. Repeated advances of glacial ice have scoured its surface and left it strewn with countless lakes, rivers, streams and ponds. Along its edge lie many of the great lakes and waterways of Canada: the eastern shores of GREAT BEAR LAKE, GREAT SLAVE LAKE, LAKE ATHABASCA and LAKE WINNIPEG; the northern shores of LAKE OF THE WOODS, LAKE SUPERIOR and LAKE HURON; and the north shore of the ST LAWRENCE RIVER.

The origin and age of the Shield were among the great mysteries of Canadian GEOLOGY. Canada's oldest rocks (3.96 billion years) were found east of Great Bear Lake. The Shield's southern limits were traced by Alexander Murray, who, in 1851-52 examined the country below Gananoque, Bytown [Ottawa], the St Lawrence and Ottawa rivers and the perimeter from Kingston to Lake Superior. A.C. Lawson made an important contribution by working out the Precambrian succession in the 1880s, but a more current time scale was not developed until the 1950s, when geologists such as C.H. Stockwell had seismic and gravity measures at their disposal (see GEOLOGICAL HISTORY). Stockwell divided the Shield into 3 great provinces - Superior, Churchill and Grenville - and 23 subprovinces. It is now considered to fall into 5 provinces: Bear, Churchill, Labrador, Southern and Grenville (see GEOLOGICAL REGIONS).

The Shield has had a profound effect on Canadian history, settlement and economic development. In pre-European times it was the home of Algonquian nomadic hunters, who developed the birchbark CANOE to travel its myriad waterways. Similar canoes were used by the COUREURS DE BOIS, VOYAGEURS and explorers to penetrate the continent.

Abundant fur-bearing animals in frontier regions provided the basis of a colonial economy until the early 1900s. The hegemony of MONTRÉAL was thus extended far into the wilderness, via the Ottawa River and connecting waterways into the North-West, creating the precedent for future Canadian sovereignty over these lands.

Canadian Shield, Satellite Image
This remote sensing image shows the rugged surface of the Shield with myriad scratches and channels gouged by the ice sheets. Sudbury, Ontario, appears as a purplish patch in the lower right (courtesy Canada Centre for Remote Sensing).

Geological Regions

Barriers to Settlement

The bare rock, thin soils, MUSKEG and insects of the Shield have presented a barrier to settlement; the agricultural frontier of the prairie provinces and eastern Canada end abruptly at its perimeter. The railway link to the West literally had to be blasted through Shield rock, coincidentally exposing its great treasures: gold, silver, nickel, cobalt, zinc, copper and iron ore. Its coniferous forests and hydroelectric power support a large PULP AND PAPER industry. Gigantic power developments at CHURCHILL FALLS, Labrador; JAMES BAY, Québec; Kettle Rapids, Manitoba; and elsewhere feed electricity to the urban south.

Boreal Shield
Saskatchewan is heavily dependent on river flows and precipitation for agricultural production (photo by Menno Fieguth).

This land of bedrock and bush has left its imprint on some of Canada's best literature, art and drama. For generations, the stark and rugged beauty of the Canadian Shield has attracted cottagers and recreationists from the urban south as well as tourists from all over the world.

Author JAMIE BASTEDO

Links to Other Sites

Ecozones and Ecoregions of Canada
Interactive website with maps and detailed descriptions about Canada's ecozones and ecoregions. Developed by Environment Canada.

Boreal Shield
An informative overview of the Boreal Shield Ecozone from the Canadian Forest Service.

Tour Canada from Space
This website features an interactive map linked to spetacular images of various Canadian locations taken by Canadian research satellites. From Natural Resources Canada.

Lake Superior North Shore
Search this Ontario travel guide for information about the Lake Superior North Shore region.

The Prehistory And Early History Of The Southern Canadian Shield Region
A great information source about archaeological research in the Southern Shield region of Ontario. Covers the Paleo-Indian Period to the 19th Century. A City of North Bay website.

Geoscape Canada
An extensive information source about the geological history, human settlement patterns, earth and water resources, and natural hazards found in locations across the country. Click on the red symbols on the interactive map of Canada to explore aerial landscapes, maps, photos, colourful online posters, and more. A Geoscape Canada website from Natural Resources Canada.

Four Directions Teachings
Elders and traditional teachers representing the Blackfoot, Cree, Ojibwe, Mohawk, and Mi’kmaq share teachings about their culture. Animated graphics visualize each of the oral teachings. This website also provides biographies of participants, transcripts, and extensive learning resources for students and their teachers. In English with French subtitles.