ECONOMIC GEOLOGY. Economic geol ogy is that branch of geology which treats of the distribution, mode of occurrence, mineral ogic content and origin of the economically valuable mineral substances occurring within the earth. The most generally recognized classification of these is into non-metallics and metallics. With the non-metallics are classi fied all those substances that are not metals in the form in which they are used. 'Clay, for ex ample, is placed with the non-metallics; though it contains the metal aluminum. All those sub stances used directly for their metal content are classed with the metallics, such as ores of lead, iron, etc.
Non-metallics.— Following are listed the more important members of this group. The natural fuels include coal, peat, petroleum and natural gas. Important building stones are granite, marble, slate, sandstone and limestone. Clay and cements may be included under ma terials of construction. Salt, borax, potash and related compounds are considered under the head of salines. Closely related to these is gypsum. The fertilizers include apatite, rock phosphate, marl, greensand and potash. Among the abrasives are novaculites, corun dum, emery, grindstones, pumice and volcanic ash, tripoli, garnet and quartz. The gems or precious stones include diamond, emerald, beryl, garnet, opal, ruby, sapphire, peridot, to paz, turquoise and many others. Minor un claisified non-metallics embrace asbestos, bar ite, diatomaceous earth, feldspar, fluorite, ful ler's earth, glass sand, graphite, magnesite, mica, monazite, sulphur, soapstone, talc, water and numerous others of lesser importance. See ABRASIVES; BUILDING MATERIALS,' COAL; CORUN DUM ; DIAMOND; PETROLEUM; SLATE.
Metallics.— The major metals are iron, copper, lead, zinc, gold and silver. Minor metals include aluminum, cobalt, manganese, mercury, nickel, platinum, tin, tungsten and many more. See COPPER; IRON; TUNGSTEN, etc.; also ORE DEPOSITS; PLACERS; MAGMATIC SEGRE GATION; VEIN, etc.
Each of the above substances is treated in a separate article which includes the mineral ogy and geology of the product.
Bibliography.— Bacon, R. F., and Hamor, W. A., (The American Petroleum Industry' (New York 1916); Bain, H. F., and others, (Types of Ore (San Francisco 1911) ; Beck, R., von den Erzlagerstat ten) (3d ed., Berlin 1909. An earlier edition has been translated into the English) ; Bey schlag, F., Vogt, J. H. L., and Krusch, P:, 'The Deposits of the Useful Metals and Rocks' (trans. by J. S. Truscott, London 1914) ; Cotta, B. von, (A Treatise on Ore Deposits) (trans. by F. Prime, New York 1870); Eckel, C. E., Ores' (New York 1914) - Economic Geology (Lancaster, Pa., 1905 to 'date); Em mons, S. F., and others, (Ore Deposits) (New York 1913) ; Emmons, W. H., Principles of Economic Geology' (New York 1918) ; The Engineering and Mining Journal (New York 1866 to date) ; Gunther, C. G., (The Examination of (New York 1912); Hilgarde, E. W., (Soils' (New York 1912) ; Johnson, R. H., and Huntley, L. G. ples of Oil and Gas (New York 1916) ; Keilhack, K., der Grund wasser-und Quellenkunde> (Berlin 1912) ; Kemp, J. F., Deposits of the United States and Canada) (3d ed., New York 1901) ; Lindgren, W. (Mineral Deposits' (New 'York 1913); Merrill, G. P., 'Non-Metallic Minerals) (2d ed., New York 1910); Phillips, J. A., and Louis, H., (Treatise on Ore Deposits' (London 1896) • Potoriii, H., 'Die Entstehung der (Berlin 1910) ; Richardson, C. H, (Economic Geology' (New York 1913) ; Ries, H., Geology) (4th ed., New York 1916) ; Spurr, J. E., Applied to Min ing) (New York 1904) ; Stutzer, 0., 'Die Wichtigsten Lagerstatten der Nicht-Erze) (Berlin 1911) • Tarr, R S., 'Economic Geology of the United States) (New York 1894); Transactions of the American Institute of Min ing Engineers (New York 1871 to date); Woodward, H. B., (The Geology of Water Supply) (London 1910) ; also the publications of the United States Geological Survey, Wash ington, D. C., and of the various State geologi cal surveys. C. L. DAKF, Professor of Geology, University of Missouri.