an island off the eastern coast of North America at the mouth of the Gulf of St. Lawrence. Cape Breton is part of the Canadian province of Nova Scotia. Area, 10,300 sq km. The island is composed of crystalline rocks. The surface is an undulating plateau, with its highest elevation 532 m (in the north); it is covered with taiga forests. In the central section of the island is Lake Bras d’Or (area, 932 sq km). There is a fishing industry. The chief population centers are Sydney and Glace Bay.