In 1963, about 75 million barrels of oil, 2.7 percent of the nation’s total, were produced in Illinois (fig. 8). This oil is valued at over $221,000,000. IS OIL PRODUCTION INCREASING OR DECREASING IN ILLINOIS? In 1940, our state had its highest yield of oil when 147,647,000 barrels were produced. Although production figures remained fairly high for some time, they have declined in the past few years. Since no new large oil discoveries have been made recently, Illinois’ total known oil reserves are decreasing yearly. In 1963, Illinois ranked eighth among the oil-producing states, with 420 oil fields consisting of 30,149 wells. COAL WHAT IS COAL AND HOW IS IT FORMED? Coal is a combustible rock that was formed by the accumulation and partial decay of vegetation. When coal was forming millions of years ago, most of the state was a low coastal plain bordered on the west and southwest by a shallow sea. A large variety of plants grew in great swamps which covered this coastal plain (fig. 9). When the plants died, they accumulated in the swamps to form thick masses of peat that were eventually covered by shallow seas and buried beneath mud and sand. Periodically, the region was above sea level, new swamps developed, new peat deposits accumulated, and more sediments were laid down. This process occurred repeatedly until over 3,000 feet of sediments had been deposited. Then the sediments were slowly compacted and hardened so that sandstones, shales, limestones, and coals were formed. [Illustration: Figure 8—Estimated total oil production by counties from 1888 through 1963.] Counties producing oil in January 1965 Total Production 2,464,758,000 barrels 46 counties producing [Illustration: Figure 9—Reconstruction of coal-forming swamp.] HOW DO WE KNOW THAT COAL WAS DERIVED FROM PLANT MATERIALS? Although plant impressions or fossilized wood can be seen in coal, they are more common in shales and sandstones associated with the coal. Often roots can be seen in the clay that lies just under the coal, and in some places stumps of trees from the coal swamp forest are preserved in the sediments adjacent to the coal (fig. 10). When pieces of coal are examined with a microscope, carbonized plant remains can be seen. HOW MANY COAL SEAMS ARE PRESENT IN ILLINOIS? There are at least 40 different coal seams in Illinois, but most are relatively thin. Seven coal seams have been mined extensively, and all together 20 or more have been mined. [Illustration: Figure 10—Some root, stem, and leaf fossils found in Illinois coal-bearing rocks.] _Neuropteris_ ⅖× _Nosopteris stem_ ⅔× _Neuropteris_ ½× _Lepidodendron_ ⅖× _Pecopteris_ ⅔× _Stigmaria_ ⅖× _Annularia_ ⅔× _Spiropteris_ ⅔× _Sphenophyllum_ 1× HOW IS ILLINOIS COAL MINED?