A massive dome of Precambrian rock dominates the Canadian landscape. Called the Canadian Shield, it lies at or near the surface of the Earth. Shaped somewhat like a giant inverted saucer, it sweeps from the Amundsen Gulf southward and eastward across the top of the Prairie Provinces, around Hudson Bay to the Atlantic Ocean, encompassing most of Ontario and Quebec and all of Labrador. The sedimentary rocks that make up the remainder of the country's surface and near surface rest on this ancient base, though it may be necessary to penetrate deeply into the Earth to find it. In the Paleozoic era (570 million to 225 million years ago) and later in the Mesozoic era (225 million to 65 million years ago), ancient seas invaded the depressed areas of the Canadian Shield and gradually formed layer upon layer of sediment. In the course of millions of years, these layers were solidified, then uplifted and broken by tremendous geologic forces. Tiny marine life trapped in the sediment formed oil and natural gas deposits that gathered in the folds of the rock. Giant dinosaurs also were covered, and they too became part of the rock layers. Some rock was melted and re-formed, and some molten rock invaded the massive cracks in the Earth's crust, where slowly it cooled and formed massive deposits of minerals. Wind and water and glacial ice wore away the rock, laying down the particles in valleys and depressions, where over the centuries living organisms have turned it into soil.

Canada may be divided into several natural regions based upon geologic history. The easternmost is the Appalachian Region, which includes the Atlantic Provinces and the Gaspe Peninsula in Quebec. This region is a northern extension of the Appalachian Mountains of the United States and, like them, is an area of lakes, rivers, and tree-clad hills. Deposits of coal, gypsum, and other nonmetallic minerals as well as metallic ores may be found in the region. Offshore in the Atlantic Ocean the frigid waters of the Labrador Current, rich in the tiny organisms upon which larger ocean life feeds, meet the warmer waters of the Gulf Stream. The resulting conditions and the presence of the continental shelf have led to the formation of one of the world's most bountiful fishing areas, the Grand Banks. In the Arctic archipelago, the frozen islands of the Canadian north, mountains similar to the Appalachians are found. Named the Innuitian Mountains after the northern indigenous people, they are largely unexplored because of the hostile climate. Thus little is known of their economic potential. Westward from the Atlantic, sandwiched between the Canadian Shield and the Appalachians, lies the region known as the Great Lakes-St. Lawrence Lowlands. Here the Mesozoic limestones, sandstones, and shales are overlain by glacial drift, the sediments left when glacial lakes drained away 11,000 years ago. This region's Point Pelee on the Ontario shore of Lake Erie, the most southerly part of Canada, is farther south than the northern boundary of California. The richness of its soils and the presence of abundant building materials have helped make this region the most populated in Canada and the center of the country's economic activity. The projection of the Canadian Shield known as the Frontenac Axis slices the St. Lawrence Lowlands in two to form the Thousand Islands in the St. Lawrence River and the Adirondack Mountains in the United States. Here the ancient granites of Precambrian rock rise above the surrounding sedimentary materials and mark the beginning of the vast expanse of barren rock, forest, muskeg swamps (grassy bogs), and beautiful lakes that are characteristic of the shield. Covering nearly 2 million square miles (5 million square kilometers), this region accounts for almost half of Canada's land area. Here are found most of the major mining activities and the evergreen forests that provide for Canada's huge forest products industry. The flow of water in numerous rivers is the source of hydroelectric power for the cities of the lowlands and for export to the United States. In a wide belt between the Canadian Shield and the western mountains, stretching from the border with the United States to the shores of the Arctic Ocean, is the region known as the Interior Plains and Lowlands. Thick, almost horizontal layers of sedimentary rock form a low, rolling landscape that rises gradually to the west. Cereal-growing areas of the eastern and central part of the region give way, as the land rises, to the cattle ranches of the west and the forests of the north. The sedimentary rock layers in Alberta yield petroleum, natural gas, and coal; in Saskatchewan they yield potash. Two other lowland areas border the shield: the Hudson Bay Lowlands and the Arctic Lowlands of the archipelago. In both the underlying sedimentary rocks are similar to those found bordering the lower Great Lakes in southern Ontario. As is also the case in the south, deposits of salt and hydrocarbons have been found, but the inhospitable climate has kept Canadians from exploiting them. A huge section of the mountainous spine of the Western Hemisphere forms the Cordillera, or Canadian Rocky Mountains, the last natural region of Canada. Monstrous geologic forces buckled and folded ancient sediments to form these chains of mountains that run roughly parallel to the Pacific shore. Rising from the interior plains and forming the Continental Divide, the Rockies were a formidable barrier to the westward expansion of the nation and continue to present problems. Only three natural passes exist--Yellowhead, Kicking Horse,
and Crowsnest--and it is through these that the produce of the prairies must pass to reach the markets of the Pacific rim. Further west, the Columbia and Skeena mountains, the interior plateaus, and the deep gorges of the Fraser and Thompson rivers also have made travel difficult through the years. Finally, the massive Coast Mountains plunge into the Pacific, forming sheer walls and a deeply indented, fjordlike coast. Vancouver Island and the Queen Charlotte Islands, projections of another fold of the Earth's crust, form the Island Mountains. In the St. Elias Mountains in the Yukon Territory to the north, Canada's highest point Mount Logan soars nearly 20,000 feet (6,000 meters) above sea level. It is almost on the border of Alaska. The Cordillera contains Canada's wettest place--Estevan Point on Vancouver Island--with more than 120 inches (300 centimeters) of precipitation each year, and one of its driest regions--the plateau in south-central British Columbia near Kamloops. Minerals and forest products and the abundant harvests of farms, rivers, and ocean make this region important to Canada.

00
Rivers and Lakes

More than 8 percent of Canada's area is covered by water, and this is still the key to the prosperity of the nation. All its major cities and towns are located on a main river or lake. Two main watersheds, or ridges that account for differences in the direction of water drainage, divide Canada. The first and most significant of these is the barrier formed by the Rocky Mountains, which separates the westward flow of water from the eastward flow. A less noticeable but important watershed is a ridge of high land that more or less follows the 49th parallel of latitude from the Rockies to the head of the Great Lakes; it separates the waters flowing northward to the Arctic Ocean or Hudson Bay from those flowing eastward toward the Atlantic Ocean or southward to the Gulf of Mexico. In the west the Fraser and Thompson rivers drain the southern half of British Columbia and pour their waters into the Strait of Georgia (between Vancouver Island and the mainland) and the Pacific Ocean. On the other side of the Continental Divide the Mackenzie River, Canada's longest, drains the waters from the Peace and Slave rivers, Lake Athabasca, and Great Slave Lake, emptying them into the Beaufort Sea and the Arctic Ocean. The North and South Saskatchewan rivers carry water from the Rockies to Manitoba's Lake Winnipeg. Together with the flow from the Red and Assiniboine rivers in southern Manitoba, these waters flow northeastward through the Nelson River to Hudson Bay. Numerous rivers from Manitoba, northern Ontario, and northwestern Quebec also flow into Hudson Bay and James Bay. Almost all other rivers in Canada flow into the Great Lakes and St. Lawrence River system and then into the Atlantic Ocean. In all the world there is no collection of fresh water to equal the Great Lakes. From Duluth, Minn., in the United States, they stretch in unbroken line through the St. Lawrence to Belle Isle, Newfoundland, a distance of more than 2,300 miles (3,700 kilometers). Canada shares all of the lakes with the United States except Lake Michigan, which lies entirely within the United States. These huge lakes have long played a major role in westward expansion and economic growth. They have eased the flow of raw materials, agricultural products, and finished goods to and from markets all over the world and have greatly enriched the two nations that share them.