P. Barnett and constructed between 1907 and 1914 in the Neo-Byzantine style. The St. Louis Cathedral, as it is known, has one of the largest mosaic collections in the world. Another landmark in religious architecture of St. Louis is the St. Stanislaus Kostka, which is an example of the Polish Cathedral style. Among the other major designs of the period were St. Alphonsus Liguori (known as The Rock Church) (1867) in the Gothic Revival and Second Presbyterian Church of St. Louis (1900) in Richardsonian Romanesque. By the 1900 census, St. Louis was the fourth largest city in the country. In 1904, the city hosted a world's fair at Forest Park called the Louisiana Purchase Exposition. Its architectural legacy is somewhat scattered. Among the fair-related cultural institutions in the park are the St. Louis Art Museum designed by Cass Gilbert, part of the remaining lagoon at the foot of Art Hill, and the Flight Cage at the St. Louis Zoo. The Missouri History Museum was built afterward, with the profit from the fair. But 1904 left other assets to the city, like Theodore Link's 1894 St. Louis Union Station, and an improved Forest Park. Neighborhoods The city is divided into 79 government-designated neighborhoods. The neighborhood divisions have no legal standing, although some neighborhood associations administer grants or hold veto power over historic-district development. Several neighborhoods are lumped together in categories such as "North City", "South City", and "The Central West End". Topography According to the United States Census Bureau, St. Louis has a total area of , of which is land and (6.2%) is water. The city is built on bluffs and terraces that rise 100–200 feet above the western banks of the Mississippi River, in the Midwestern United States just south of the Missouri-Mississippi confluence. Much of the area is a fertile and gently rolling prairie that features low hills and broad, shallow valleys. Both the Mississippi River and the Missouri River have cut large valleys with wide flood plains. Limestone and dolomite of the Mississippian epoch underlie the area, and parts of the city are karst in nature. This is particularly true of the area south of downtown, which has numerous sinkholes and caves. Most of the caves in the city have been sealed, but many springs are visible along the riverfront. Coal, brick clay, and millerite ore were once mined in the city. The predominant surface rock, known