The Physical Structure of Canada

THE PHYSICAL STRUCTURE OF CANADA A. P. COLEMAN C ANADA> with an area of 3,603,9IO square miles, . is one of the largest countries in the world and surpasses Australia and India among the divisions of the British Commonwealth, and also the United . States; so that its ten million people seem to have ample room to expand. But area alone by no means determines the prosperity of a nation. It may prove a hampering influence and a danger where a small population is scattered in widely separated regions having different interests and different outlets for their commerce. In earlier days there was a real risk that British North America,peopled by separate groups on the Atlantic, the Great Lakes, the Prairies, and the Pacific, might never unite to form a single nation, since apparently impassable barriers separated the different parts of the country. There was a time when Nova Scotians talked of "going to Canada;" and even yet there is sometimes a hint of separatism, amd certain curious forms of speech point toward disjunctive trends. If a dweller in ·central Canada speaks of going to the "coast" it is well understood that he is bound for the Pacific. In the popular mind of Ontario there is no Atlantic coast. On the other hand the "Maritime Provinces" do not include British Columbia, although its coast-line is vastly longer than that of Nova Scotia and New Brunswick combined. The separate groups into which the country is naturally divided have, of course, their foundation in the geological history of Canada, going back, in part, for more than a billion years. Some of our difficulties SII THE UNIVERSITY OF TORONTO QUARTERLY in developing the coun try can be traced to mountainbuilding operations dating from the world's earliest youth; and some of our most important resources are found in very ancient formations of which the history is obscure. On the other hand, our sources of water power and our Great Lakes (for navigation) have come to us from the most recent period of geological history when great ice-sheets covered 11he land. The economic development of Canada is very closely bound up with the distribution of the rocks, and the minerals they contain; and her routes of communication have been largely determined by physiographic features. Roughly speaking, the geological map of Canada can be divided into two nearly equal parts : one which took shape in Pre-Cambrian times, consisting mainly of very ancient igneous and crystalline rocks, and another including all the later format'ions, mostly sedimentary, often still lying much as they were laid down on the sea bottom, but in places faulted or folded or penetrated by later eruptive rocks. This twofold division of the geological formations is not symmetrical, however, since the ancient rocks lie mainly on the north-eastern side and the later sediments occupy three separate areas, a small and narrow one to the south-east, a very broad one to the sou th-west, and a scattered group around Hudson Bay and in the arctic islands to the north. The distribution here indicated has profoundly influenced the development of the country. An ou cline of the geology of Canada naturally begins with the vast foundation of ancient rocks generally called the Canadian or Pre-Cambrian Shield, which not only makes half of its surface but underlies, sometimes at no great depth, all the later formations. For the most part these fundamental rocks are granite and 512 THE PHYSICAL STRUCTURE OF CANADA gneiss, which were once molten, but it is astonishing to find that the earliest rocks of all were formed under water. The Grenville series of southern Ontario and Quebec consists largely of limestone, and the Keewatin rocks of the north and north-west, though mainly lava and volcanic ash, include long bands of "iron formation" of quartz and ore in alternate layers, evidently laid down under water. One of the most puzzling enigmas of Canadian geology here presents itself: no floor has been found beneath the Grenville sediments and the Keewatin lavas. They are always cradled in the Laurentian granite and gneiss which rose from beneath as molten magma, swelling up as great oval batholiths...