HOW EXTENSIVE ARE CLAY DEPOSITS IN ILLINOIS?
Clay deposits in Illinois consist of Quaternary clays, which were deposited by glaciers, lakes, and winds; and of fireclay, shale, kaolin, and “fuller’s earth,” all of which are bedrock deposits. Quaternary clay, fireclay, and shale resources occur widely in very large quantities; “fuller’s earth” and kaolin deposits are small in relation to other clay resources.