Missouri bituminous coal occurs in the northern and western parts of the state. It contains bands of dull coal, bands of glistening “glance” coal, the sooty “mineral charcoal,” and common mineral impurities like calcite, gypsum, pyrite and marcasite (“sulphur”), clay minerals, and quartz. Bituminous coal breaks with essentially a cubical fracture. It occurs in horizontal or nearly horizontal beds or “seams,” which may be followed considerable distances laterally without necessarily encountering much change. Usually, a fire clay or a fire clay-like under-clay immediately underlies the coal, but the overlying rock (the roof) may be shale (slate? see discussion of SHALE), sandstone, or less commonly, limestone. [Illustration: Bed of coal exposed by stream erosion, near Columbia.] Coal originates from pre-existing plants and may be thought of as Mother Nature’s storage cellar of “preserved” plant life. The Missouri coal began millions of years ago as mosses, tree-like ferns, conifers, and various plants that reproduce by spores, which flourished in great wide-spread swamps. Insects were abundant, as is indicated by their remains. Rain was probably plentiful and climate favorable, so that such vegetation thrived luxuriantly. Today, fallen forest timber of the highland disappears by oxidizing and decaying in the air; but in swamp land the leaves, stems, pollen and woody trunks fall into and under water and under favorable conditions decompose through bacterial and chemical action into layers and pools of slippery, oozy, blackish humic gel (like brownish black gelatin, “jello”), which remains. Likewise, in ages past, more and more plant material continued to live, fall, and accumulate in the old coal swamps until very thick deposits of the woody gel existed. Eventually land-sea or climatic conditions changed, and plant life died out as mud, sand, or other rock-forming material was swept in to cover, as a lid, the stored-up plant remains. The weight of overlying beds squeezed out excess water from the woody gel, and from the time of covering through the present day, gases (like mine gases), and other volatile constituents of the coal have been given off. A bed of coal, which consists chiefly of black combustible carbon, with volatile constituents and non-volatile ash substances, has resulted. Man uses the coal by burning it directly, or it may be coked and the volatile constituents recovered in coal tar and other compounds. The mineral impurities like the calcite, gypsum, clay, sand, and brassy pyrite or marcasite, are shaken through the grates as ash or melted as clinkers. In nature, the pyrite and marcasite minerals may oxidize in ground water percolating over them to form dilute sulphuric acid, the acid mine waters.