sedimentation, and Most mountain building. invertebrates probably present, but remains are lacking. Archeozoic 800 ± M.Y. World-wide Blue-green algae intrusive igneous present, activity; some primitive sediments. one-celled plants and animals probably present. BIBLIOGRAPHY MINERALOGY _Getting Acquainted with Mineralogy._ By G. L. English, 1936, McGraw-Hill Book Co. A beginning textbook of mineralogy. _Introduction to the Study of Minerals and Rocks._ 3rd Edition, by A. F. Rogers, 1937, McGraw-Hill Book Co. Describes the commoner minerals systematically. _Dana’s Textbook of Mineralogy._ 4th Edition, revised by W. E. Ford, 1932, John Wiley and Sons. Detailed descriptions of minerals, their physical properties, and their occurrence. _Manual of Mineralogy._ 15th Edition, by E. S. Dana, revised by C. S. Hurlburt, 1941, John Wiley and Sons. A textbook of mineralogy. MINERAL ECONOMICS, GEOPOLITICS _World Minerals and World Peace._ By C. K. Leith, J. W. Furness, and Cleona Lewis, 1943, The Brookings Institution. Physical, economic, and political trends in the mineral industry. _Minerals in World Affairs._ By T. S. Lovering, 1943, Prentice-Hall. _Minerals Yearbook._ U. S. Bureau of Mines. An annual volume presenting statistical data on the production of the mineral resources of the United States. Reports on individual minerals or rocks may be had separately. ECONOMIC GEOLOGY _Mineral Deposits._ 4th Edition, by W. Lindgren, 1933, McGraw-Hill Book Co. The manner of occurrence and origin of mineral deposits. _Elements of Engineering Geology._ 2nd Edition, by H. Ries and T. L. Watson, 1947, John Wiley and Sons. _This Fascinating Oil Business._ By M. W. Ball, 1940, Bobbs-Merrill Co. A simple and elementary description of the petroleum industry. _Geology of Coal._ By O. Stutzer and A. C. Noe, 1940, University of Chicago Press. GENERAL GEOLOGY _Down to Earth._ By C. Croneis and W. C. Krumbein, 1936, University of Chicago Press. An introduction to geology, profusely illustrated. _Textbook of Geology Part I—Physical Geology._ 4th Edition, by C. R. Longwell, A. Knopf, and R. F. Flint, 1939, John Wiley and Sons. A standard text on geology.