This map shows the sedimentary rocks, all of Paleozoic age, that lie between the glacial deposits and the extremely old (Precambrian) basement rocks making up the heart of the North American continent. They are mostly known from boreholes, mines and excavations rather than outcrops.
The Paleozoic rocks are draped over four underlying tectonic structures: the Illinois Basin to the southwest, the Michigan Basin to the northeast, and an arch running northwest to southeast that is called the Kankakee Arch on the north and the Cincinnati Arch on the south. The arches have lifted the layer-cake of rocks so that the younger beds have eroded away to reveal the older rocks beneath: Ordovician (about 440 million years old) in the Cincinnati Arch and Silurian, not quite so old, in the Kankakee Arch. The two basins preserve rocks as young as Mississippian in the Michigan Basin and Pennsylvanian, youngest of all at about 290 million years, in the Illinois Basin. All of these rocks represent shallow seas and, in the youngest rocks, coal swamps.
Indiana produces coal, petroleum, gypsum and huge amounts of stone. Indiana limestone is widely used in buildings, for instance in Washington DC's landmarks. Its limestone is also used in cement production and its dolostone (dolomite rock) for crushed stone. See a gallery of Indiana geological attractions.
More Indiana resources on About.com:
Indiana Geography, State Symbols & Facts
Indiana National Parks
Best Indiana State Parks in the Spring
Best Indiana State Parks in the Winter
Indiana Campground Reviews