Yes. In the area underlain by the basin, stone quarries are operated in younger, thinner rock strata of Pennsylvanian age. These strata also overlie the thick limestones and dolomites quarried along the margins of the state. The quarries located within the basin area produce stone for agricultural limestone, roads, and other purposes. HOW AND WHERE ARE LIMESTONE AND DOLOMITE USED? Millions of tons of stone are crushed annually to produce aggregate for use in making concrete roads and buildings, for road surfacing, and for agricultural limestone. Agstone is applied to farmlands to neutralize soil acidity, improve soil structure, add calcium and magnesium, and promote conditions favorable for the utilization of soil materials by plants. Large quantities of limestone are used in making lime and cement. There are three cement plants in northern Illinois—two at LaSalle and one at Dixon—and one in southern Illinois, at Joppa. Small amounts of stone are used for making alkalies and glass, for railroad ballast, for building stone, for dusting coal mines to prevent coal dust explosions, and for ingredients in mineral feeds for livestock. HOW MUCH STONE DOES ILLINOIS PRODUCE? A production of about 36 million tons of stone in 1963 was valued at almost $48,000,000. The cement made from Illinois limestone in the same year was valued at $32,000,000. CLAY WHAT IS CLAY AND HOW IS IT FORMED? Weathering or alteration of some rocks produces clay which is a very fine-grained, unconsolidated rock. Clay is made up of a group of minerals, of which illite, montmorillonite, kaolinite, and chlorite are the most abundant. 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. HOW IS ILLINOIS CLAY USED? Surface clay, shale, and fireclay are used in the manufacture of structural clay products, such as brick, drain tile, and hollow block (fig. 16). Fireclay is used for a bonding agent in molding sand, for the making of stoneware vessels, for a plaster on the walls of industrial furnaces, and for making refractory brick. Refractory brick must be able to withstand very high temperatures and is used to line industrial furnaces, boilers, kilns, and ladles for molten steel. Shale and clay are ground up and mixed with limestone in the manufacture of cement. Crucibles, refractories, china, and porcelain are made from kaolin. “Fuller’s earth” is used as a sweeping compound and as an animal litter. [Illustration: Figure 16—Typical Illinois bee-hive kiln.] WHAT IS THE VALUE OF THE CLAY PRODUCTS MANUFACTURED IN ILLINOIS?