Québec is divided into three main geological regions: the St. Lawrence Lowlands embedded between the Precambrian Massif of the Canadian Shield, north of the St. Lawrence River, and the Appalachians to the south. These natural boundaries extend beyond Québec territory.
- The St. Lawrence Lowland is a plain along the St. Lawrence River. The bedrock essentially consists of very ancient rocks dating back to the Paleozoic era, some 250 to 500 million years. They are mostly sedimentary rocks formed by the accumulation of sediments in a sea or ocean. Québec’s best fertile farmlands are located in the St. Lawrence Lowland.
- The plateau Laurentien or Canadian Shield occupies nearly 95 percent of the area of Québec. The Canadian Shield, dating to the Precambrian era, is the most ancient geological formation in the world that is more than two billion years old. It is an area mostly composed of igneous rocks mainly granites, but also metamorphic and sedimentary rocks. It is bounded on the south by the Laurentides (Laurentians) mountain chain which skirts the St. Lawrence River.
- In the Appalachian region located south of the river, lies a narrow stripe of old mountains with rounded peaks along the south-east border of Québec. The Appalachians like the St. Lawrence Platform consist of Paleozoic rocks.
All these mountains have been leveled by millions of years of systematic erosion and by glacier motion. Their elevations vary from 300 to 600 meters only. The highest peaks in Québec are Mont D’Iberville (1,622 m / 5,321 ft.), located in Nunavik’s Torngat mountains, and Mont Jacques-Cartier (1,268 m / 4,160 ft.), part of the Chic-Chocs mountain range in the Gaspésie.