Geography of Montreal - Geology

Geology

There are three main geological regions in Quebec: the great igneous plains of the Canadian Shield, the Appalachians in southern Quebec, and the St. Lawrence lowlands that lie between them. Covering over 95% of Quebec, the Canadian Shield contains some of the oldest igneous rocks in the world, dating back to the Precambrian period, over 1 billion years ago. The Canadian Shield is generally quite flat and exposed, punctuated by the higher relief of mountain ranges such as the Laurentians in southern Quebec. The Appalachian region of Quebec is a thin strip of weathered mountains along Quebec's southeast border. The Appalachian mountain chain is actually a long range that runs from Alabama north to Newfoundland. The St. Lawrence lowlands are comparatively tiny in size (about 17 280 square kilometres) but disproportionately important in that they contain most of the human population of Quebec. The lowlands actually consist of three parts: the central lowlands, or the St. Lawrence Plain, a wide and flat triangle extending from Cornwall to Quebec City. The St. Lawrence Plain is almost entirely flat because of the clay deposits left behind by the Champlain Sea (which once covered all of Montreal).