GEOLOGY. While the geological structure of Canada exhibits a variety of detail that is com mensurate with the vast area and diversified surface of the country, in a broad aspect it is simple and can be easily explained. The most ancient rocks found in Canada, and in North America as well, are the granites, gneisses, and sehists which underlie a great V-shaped area, hav ing Hudson Bay in centre, and extending from the Great Lakes northeast to the Labrador coast, and northwest to the shores of the Arctic Sea. This area was once diversified by mountains, which are represented at the present time, after an immeasurably long period of erosion, by the Laurentian plateau. The age of the granites and banded rocks is Archican. On the borders of this primitive land area stratified beds have been deposited during all the succeeding geological periods. The Cambrian and Silurian systems are represented by great thicknesses of strata that outcrop in Nova Scotia, New Brunswick, New foundland, along the Saint Lawrence Valley, and on the shores of Lake Ontario. They also appear farther west in extending thence in a northwesterly direction toward the Arctic re gions, and into British Columbia. The Devonian System is less extensively developed in the east ern provinces, but it constitutes a wide belt in the prairie regions which border the Cambrian and Silurian strata. Between this Devonian belt and the Eastern Rocky Mountains the surface is formed by Cretaceous and Tertiary beds that are a part of the great series reaching northward from Texas across the United States. The
Rocky Mountains of Canada are similar in struc ture to the mountains of Colorado, Wyoming, and and have beret built up by upheaval and folding of sediments, and, to a lesser extent, by volcanic action. The strata of which they are composed range in age from Paleozoic to Ter tiary. while in the Selkirk,: even the Archaean may be present. The Carboniferous System is not especially important in respect to area, but it contains the valuable coal deposits of Nova Scotia and New Brunswick, and is known to occur also in the central prairie region, in British Co lumbia. and along the Arctic coast. The coal beds of Vancouver Island and those found in the Rocky :Mountains art' of Cretaceous and Ter tiary age. In recent geological times nearly the entire area of Canada was covered by an ice sheet, the Laurentian glacier, that terminated iu the northern United States. The surface features were profoundly modified by the erosive: action of this vast mass of moving ice, as is evidenced by the numerous great lakes,. and by the ex tensive deposits of sands, gravels, and clays that rest upon the older geological formations. See also Geology, under BRITISH CoLumm A ; ON TARIO ; etc.