Date Published:
July 2005

L’Encyclopédie de l’histoire du Québec / The Quebec History Encyclopedia

Geology of Canada

[This article was written in the 1930's and published in 1948. For the precise citation, see the end of the document.]

Geology. Canada is geologically one of the oldest countries in the world, and more than half of it consists of Precambrian rocks, which, so far as is known, have been above the sea ever since the beginning of the Palaeozoic. The "Canadian Shield" formed the vast nucleus about which the North American continent has been built up from that time to the present, and the later rocks have been deposited, layer after layer, in the shallow seas around its margins. The Precambrian of Canada is not symmetrically placed, however, since the western side of the country consists almost wholly of later rocks, while the great peninsula of Labrador on the east belongs wholly to the unfossiliferous Archaean series.

In an outline like the present only the more prominent points can be mentioned, and only brief references can be made to the main subdivisions of the geology as displayed in the more populous southern part of the country.

The Canadian Precambrian shield consists very largely of Laurentian granite and gneiss, eruptive rocks which came up through older sedimentary materials (Grenville) now changed to marble and quartzite and gneiss, or through great beds of lava (Keewatin). These areas of ancient crystalline rocks in the beginning formed ranges of mountains, which seem to have covered mast of the shield, but which were worn down in the lapse of ages to a peneplain, now displaying only rounded hills and shallow valleys. Rocks of this age form the rugged north shore of the St. Lawrence below Quebec, the picturesque Thousand islands, and the rocky country near Ottawa and on the east and north of Georgian bay and lake Superior. These most ancient formations are somewhat barren of useful minerals, and very little mining has been done upon their deposits. On this early floor Timiskaming sediments were laid-down and penetrated by a later granite (Algoman), which brought with it gold in northern Ontario at Porcupine and Kirkland lake. Still later, a Huronian ice age, the earliest known in the world's history, deposited the Cobalt conglomerate noted for its silver ores. Finally, in the Keweenawan, the latest part of the Precambrian, there were eruptions of basic rock, such as norite, bringing with them nickel, copper, lead, and zinc in the Sudbury region.

The later divisions of the Precambrian just mentioned cover much less space than the early barren granite and gneiss. The Keweenawan sandstones, shales and great sheets of diabase give rise to picturesque table-topped hills and low mountains north of lake Superior, especially near Thunder bay. Dipping southwestward from the ancient shield in southern Quebec and Ontario there are Palaeozoic sandstones, limestones, and shales of Ordovician, Silurian, and Devonian age, laid down in a shallow sea and often containing trilobites, brachiopods, and other fossils. They are to be seen on the flanks of mount Royal, along lake Ontario, and especially at Niagara, where the cliffs of the gorge display splendid sections.

The Carboniferous and Permian of the later Palaeozoic cover much of the Maritime provinces, and may be studied at Sydney or the Joggins in Nova Scotia and near the bay of Fundy in New Brunswick. Except for some marine beds of the Carboniferous in the Rocky mountain region, no other part of Canada includes rocks of this important coal-bearing age.

The Mesozoic covers far more space than the Palaeozoic and makes up almost the whole of the great plains south-west of the Precambrian nucleus of the continent. The latest division of the Mesozoic, the Cretaceous, is of chief importance, and its flat-lying sediments underlie most of the typical prairie region of the west, affording excellent soil and containing large deposits of lignite coal of varying quality. Most of the Cretaceous beds are of land or fresh water origin, and at some points they include great numbers of dinosaur remains. Good examples of skeletons of these huge reptiles may be seen in the Victoria Museum of the Geological Survey at Ottawa and at the Royal Ontario Museum in Toronto.

After the Cretaceous beds were formed at or near sea level, the Rocky mountains were elevated, and 20,000 feet or more of sediments were thrown into great folds or split into long blocks which were tilted and driven upon one another, forming the bare cliffs which give the name to the chain and which rise so suddenly and impressively from the monotony of the prairie.

The Rocky mountains proper have a width of about sixty miles and reach heights of 8,000 to 10,000 feet in most places, with a few peaks above 12,000, culminating in mount Robson at 12,972 feet. In the central and western parts there are many glaciers, and midway between the Canadian Pacific and Canadian National Railways the Col­umbia ice field covers 110 square miles. From it glaciers reach down into the valleys, feeding rivers which flow to the gulf of Mexico, the Arctic ocean, and the Pacific.

West of the Rockies are the Selkirk and Gold ranges, older and not quite as high, but snowier because nearer the Pacific, the source of moisture. Then follows the interior tableland of British Columbia, cut by profound valleys and canyons and containing beautiful lakes. This part is semi-arid, and requires irrigation for the fruit orchards toward the south.

Finally comes the Coast range of mountains, formed in Jurassic times by the upwelling of molten rock, much like the Laurentian of eastern Canada. Parts of the older rocks which it hoisted up form "roof pendants", which have been greatly metamorphosed and often contain important ore deposits. The highest mountains in Canada south of the Yukon territory have recently been discovered in the Coast range, including mount Waddington, which reaches 13,260 feet. Far to the north, mount Logan attains 19,850 feet, the highest point in Canada, and is surrounded by other lofty peaks in a tableland of snow and ice covering thousands of square miles and reaching the wild coast of Alaska to the south.

The three mountain chains just mentioned form the Cordillera and make up most of British Columbia; but still farther to the west rises another discontinuous range in the great island of Vancouver and the smaller Queen Charlotte islands, a chain now half submerged.

Toward the west in the interior plateau and in parts of the mountains along the Pacific, there are lava fields and comparatively modern volcanoes, such as mount Garibaldi, north of Vancouver, but no eruption has been known in historic times, though in Alaska to the north there are several active volcanoes. The most recent of the mountain ranges, the Rockies, contains no eruptive rocks, unlike the chains to the west, which are largely eruptive.

Thus far the bed-rock geology of Canada has been outlined, and the fact has been noted that its eastern half consists chiefly of the most ancient of known rocks. But Canada is not- only the oldest, but also the youngest country in the world, since its present surface, its lakes and rivers and its scenery, have been profoundly modified and impressed by events in the latest part of geological time, the Pleistocene. Nearly the whole of the country has been covered with ice sheets within the last million years, and this has happened more than once, with the result that a very ancient land surface, which must have been buried under the débris caused by weathering during the ages, has been completely renovated. Three vast ice sheets accomplished the work, a Cordilleran sheet which covered British Columbia and reached the islands along the coast, a Keewatin sheet which blotted out the whole of the great plains, and a Labrador sheet which covered all of the east except one or two fringing mountain ranges. Almost everywhere in Canada the effects of these tremendous machines are in evidence. In the north the bare rocky hills show the scouring, polishing, and striations made by advancing ice; while toward the south there are gently undulating stretches of boulder clay making excellent farms; or in places the tumbled hills and kettle-shaped valleys of moraines where the ice sheet halted, perhaps for thousands of years, dumping the débris borne from the north hundreds of miles from its source.

To the traveller, the granites and gneisses scattered here and there as erratic blocks in the field give striking evidence of ice work. From the windows of the train as one crosses the prairie one may see pink granites or green schists from the central Archaean region distributed by the Keewatin ice sheet for hundreds of miles over the Cretaceous beds of the plains. They may be found along Bow river at Calgary within sight of the Rockies, and west of Edmonton on the way to the Athabaska pass.

In Ontario the work of the ice has been of tremendous importance, since the Great lakes are largely due to the irregular dumping of moraines, blocking an ancient river valley which drained the region to the Atlantic. Not alone lakes but waterfalls, such as the Sault Ste. Marie between lake Superior and lake Huron, Niagara falls between Erie and Ontario, and the rapids of the St. Lawrence between Ontario and sea level, resulted from the unequal distribution of drift.

A glance at the map of Canada shows innumerable lakes of all sizes and shapes, far more than in any other country. Many of them are crowded with islands, as in Georgian bay and lake of the Woods, where there are thousands. They are evidently tracts of hilly country flooded by the blocking of old river channels. The larger lakes, however, sometimes have depths hundreds of feet below sea level, so that they can never be drained, indicating important warpings and changes of level since they belonged to a continuous river valley: but the chief factor in their formation was the barriers of boulder clay and moraine left by the ice invasions.

The value of Canadian lakes and waterfalls, for communication and for electric power, has been very great, particularly in Ontario; and it is not too much to say that these gifts of the ice age have determined the fate of Canada as a separate country from the great nation to the south. The St. Lawrence and Great lakes were the highway of the early French fur-trade, which paradoxically made Canada British instead of American in the long run; and the lakes have existed only since the ice left the region.

The geological factors of main importance for the development of Canada have been the Precambrian shield, with its ores of metals stored away a billion years ago; the flat Cretaceous beds, with their immense supplies of coal and lignite making the prairie; and the rejuvenating work of the great ice sheets providing rich soil, easily harnessed water powers, and a great chain of lakes for inland communication.

See A. P. Coleman and W. A. Parks, Elementary geology, with special reference to Canada (London, 1922).

Source  : W. Stewart WALLACE, ed., The Encyclopedia of Canada, Vol. III, Toronto, University Associates of Canada, 1948, 396p., p. 23-26.