Indiana ranks 38th among the states in size, with a total area of 94,322 sq km (36,418 sq mi), including 818 sq km (316 sq mi) of inland water and 609 sq km (235 sq mi) of Lake Michigan over which it has jurisdiction. Indiana is roughly rectangular in shape, and the state has a maximum dimension north to south of 459 km (285 mi) and a maximum east to west dimension of 285 km (177 mi). The state is bordered on the north by Lake Michigan and the state of Michigan, on the east by Ohio, and on the west by Illinois. The Ohio River separates Indiana from Kentucky on the southern border.
Indiana includes parts of two natural regions, or physiographic provinces, of the United States, the Central Lowland and the Interior Low Plateau. Both regions form part of a larger natural region, the Interior Plains. Indiana lies mainly between 150 and 300 m (500 and 1,000 ft) above sea level and has an average elevation of about 210 m (700 ft). The highest point, in Wayne County near the Ohio state line, is only 383 m (1,257 ft) above sea level.
The Central Lowland, in Indiana, is a generally flat area that covers the northern and central portions of the state. Much of its appearance is a result of glacial action that occurred during the Ice Age, which ended about 10,000 years ago. During that period several great ice sheets advanced from the north and retreated across Indiana. Early ice sheets covered all of Indiana except a hilly irregular wedge roughly south of a line connecting the cities of Evansville, Bloomington, and New Albany. Later ice sheets covered only the northern and central sections of the Central Lowland. The ice sheets left a deep layer of glacial drift that has weathered into soils made up of sand and clays intermingled with gravel. This type of glacial drift is termed till, or ground moraines.
Occasional areas of boulders and rough stones were deposited in terminal or lateral moraines, now rising in low, deeply eroded hills marking the edges of the glacier’s path. As the glaciers melted, they left deposits of sand and gravel washed out by meltwater streams. These deposits form a natural conduit for groundwater and are the source of well water in large parts of the state.
The most recently glaciated areas, limited to northern Indiana, are covered with large areas of infertile sandy deposits and numerous swamps and marshes. When drained, the swamps and marshes provide fertile muck soils. Low sandy ridges and hills of glacial drift are common in this section of the Central Lowland. Central Indiana, which has a generally less varied relief, includes the flattest areas in the state and also some of the most fertile soils.
The very flat and fertile lands of west-central Indiana form an extension of the Grand Prairie area in Illinois. Only in some east-central areas do concentric bands of low sandy ridges add greater diversity of relief. Glaciated areas in southern Indiana, covered very early in the Ice Age, have been exposed longer to the forces of erosion than have the areas farther north. As a result, the landscape in even the glaciated areas of southern Indiana is characterized by numerous rolling hills and valleys.
The Interior Low Plateau, in southern Indiana, is a hilly area that was never glaciated by the ice sheets. Long subjected to erosion, it is an area of sharp ridges, deep gorges and scenic waterfalls. There are also numerous caves and sinkholes, which have been formed in places where water action has dissolved the underlying limestone of the plateau. Wyandotte Cave and Marengo Cave, about 50 km (about 30 m) west of New Albany, are two of the largest caves. Limestone bedrock exposed in the unglaciated areas provides the state with a major building stone, Indiana limestone. One of the world’s leading exposures of Devonian Period limestone fossils is in the Falls of the Ohio State Park in New Albany. "Indiana" © Emmanuel BUCHOT, Encarta, Wikipedia
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