The structure and nature of coke make it a valuable fuel for blast furnace use in the production of steel. In the past, most of the coal used in the manufacture of coke has come from areas of higher quality coal outside of our state. However, at present, over 1,000,000 tons of Illinois coal are mined annually for the production of metallurgical coke. [Illustration: Figure 12—Estimated total coal production by counties from 1882 through 1963.] Area underlain by coal-bearing rocks Counties producing coal in January 1965 Total Production 3,749,423,534 tons 71 counties producing STONE AND STONE PRODUCTS WHAT TYPES OF STONE ARE PRODUCED IN ILLINOIS? Limestone and dolomite are the most abundant rocks quarried in Illinois. Small amounts of marble, limestone, and sandstone for building stone are also produced. In addition, some glacial boulders and cobbles are used for rock gardens and in home construction. The crushed limestone industry is Illinois’ most important rock products industry. WHAT ARE LIMESTONE AND DOLOMITE? Limestone is a sedimentary rock that consists chiefly of calcite, which is composed of calcium, carbon, and oxygen. Dolomite is a variety of limestone that contains considerable magnesium in addition to the other elements. Limestones were deposited on the floors of ancient seas that repeatedly covered most parts of Illinois. Shelled creatures, corals, and coral reefs helped build up the thick limestone deposits (figs. 13 and 14). [Illustration: Figure 13—Piece of limestone largely made up of fossil brachiopod shells.] WHERE ARE LIMESTONE AND DOLOMITE QUARRIES LOCATED IN ILLINOIS? Limestone and dolomite quarries are located along the southern, western, and northern margins of the state where the thick deposits of these rocks crop out at the surface. Although bedrock was deposited in horizontal layers, it has since been downfolded into the Illinois Basin whose center is in southeastern Illinois. Thus, the thick limestones and dolomites that are quarried along the margins of the state are too deeply buried to be quarried in the central part of this basin (fig. 15). [Illustration: Figure 14—Fossils commonly found in Illinois rocks.] _Strophomena_ 1× _Paleoneilo_ 1× _Ctenodonta_ ⅔× _Dolmanites_ ½× _Archimedes_ 1× _Hormotoma Polygyra_ 1× _Mucrospirifer_ 1½× _Atrypa_ ⅔× _Crinoid Columnais_ 1× _Halysites_ ⅔× _Hexagonaria_ 1× _Microcylus_ 1× _Streptelasma_ ⅔× _Lithostrationella_ ½× _Lophophyllum_ 1× [Illustration: Figure 15—Diagrammatic cross section of the Illinois Basin.] _MISS. RIVER_ Waterloo Mt. Vernon ILLINOIS _WABASH RIVER_ INDIANA New Albany _OHIO RIVER_ ARE ANY STONE QUARRIES LOCATED IN THE AREA UNDERLAIN BY THE ILLINOIS BASIN?