The geologic map of Illinois prepared by the Illinois State Geological
survey shows, with reasonable exactness, what bedrock formations would
crop out at the surface if the overlying clay, sand, gravel, and earth
were removed. Thick dolomite formations would be exposed in much of the
northern fifth of the state, but would be rare elsewhere. Thick
limestone formations would occur in an almost continuous zone, varying
in width from 3 to 25 miles, along the Mississippi River from Rock
Island to southern Illinois and then eastward across the extreme
southern tip of the state. Limestone also would be seen along the
Illinois River from Havana southward.
In the central area of the state, limestones are present, but they are
rarely over 25 and often less than 15 feet thick. Consequently, most of
the larger quarries are in the northern, western, and southern parts of
Illinois. The thinner limestones, nonetheless, are of much importance
and are quarried at many places, chiefly to provide agricultural
limestone, road stone, and limestone for making cement.
The Geological Survey locates and maps limestone and dolomite deposits
and analyzes and tests samples to determine the best possible uses for
the stone. Many reports have been published about the character and
general use of the deposits in various parts of the state. Other reports
deal with the use of limestone and dolomite for specific purposes such
as cement making, building and decorative stone, rock wool, terrazzo
chips, and lime.