widens into Lake Saint-Louis as it approaches the island. Around a southern point near the center of the island, the St. Lawrence narrows into the Lachine Rapids, then widens into the Bassin de La Prairie past that southern point, and narrows again at the Montreal neighborhood of Cite Du Havre before flowing towards Quebec City and the Atlantic Ocean. The Lachine Canal on the island bypasses this complex part of the river. Neighboring islands in the St. Lawrence include Saint Helen's Island, Notre Dame Island, and Nuns' Island. The topography of the island has been significantly altered by human activity, as evidenced by historical maps that name a lake St. Pierre in the island. This lake, and several other watercourses, have been drained or covered over as the city developed, while areas on the island's shores have been reclaimed and extended. The southwest of the island is separated by the Lachine Canal between Lachine and Montreal's Old Port; this portion of the island is partially divided further by the Canal de l'Aqueduc, running roughly parallel to the Lachine Canal, beginning in the borough of LaSalle and continuing between the boroughs of Le Sud-Ouest and Verdun. Most of the bedrock of the island consists of Chazy limestone, with some Utica shale. At the centre of the island stand the three peaks of Mount Royal, a volcanic intrusion (not an extinct volcano, contrary to popular belief). This short mountain (elevation 233 metres, 765') is a member of, and gives its name to, the Monteregian Hills. Human geography The island of Montreal is the major component of the territory of the city of Montreal, along with Île Bizard, Saint Helen's Island, Notre Dame Island, Nuns' Island, and some 69 smaller islands. With a population of 2,014,221 inhabitants (22% of the population of Québec), it is by far the most populous island in Canada. It is also the 6th most populous island of the Americas and the 37th most populated island on Earth. In addition, it is the world's most populous island surrounded by fresh water. Montreal and the other municipalities on the island compose the administrative region of Montréal. The area of the Urban agglomeration of Montreal, which includes the Island of Montreal and several other smaller islands, is 499 km2 (193 sq. mi.). The crossings which connect the island to its surroundings are some of the busiest bridges in the country and