Further variations in distribution might be caused by greater or less original content of the strata in nitrogen. In fact among such purely conjectural postulates, it is interesting to note the general parallelism between the richer nitrate fields, the Cordilleran lines of intrusion and the present volcanic range of the Andes. The relation of the latter two lines indicates an ancient direction of structural weakness present as early as late Cretaceous. It might be inferred that this direction still earlier may have determined a line of Mesozoic volcanic vents and that the richer nitrate concentrations have been possible on this line. Speculation of this nature is, however, by no means essential to an explanation of the richer deposits. Where scattered deposits of small area are found, topographic conditions are unfavorable to nitrate concentration. The larger, irregular, nitratebearing areas of the south, Taltal, Aguas Blancas and Antofagasta, occur in topography of early maturity. The narrow and more regular deposits of Tarapacá and Tocopilla lie on the mature slopes bordering plains of desert old age. The lack of continuity of the latter deposits is probably determined by projections into the Coast Range of the plains of the Tamarugal Valley between Tarapacá and Tocopilla and south of Tocopilla. The decrease in area of the deposits, proceeding from south to north, with a somewhat parallel increase in richness is in striking correspondence to the development of desert erosion. The distribution of nitrate, as modified by processes of concentration, is thus in full agreement with origin from the lower Jurassic volcanic strata. CONCLUSIONS. The volcanic origin of the nitrate of the Chilean deposits is probable and adequate; it appears furthermore to be a satisfactory explanation of the facts of salt association, of occurrence and of distribution of the deposits and is, therefore, presented with confidence. The mode of concentration by superficial, intermittent waters, causing slow downward migration of salts during the development of the present desert topography, is ac cepted as the only method explanatory of the features of deposits in all the Chilean fields. Thus a unique type among mineral deposits is due to unusual causes; the profitable industry of today owes its existence to merely a fortuitous combination of chemical relations and of geologic, physiographic and climatic conditions. MASS. INSTITUTE OF TECHNOLOGY, CAMBRIDGE, MASS. BIBLIOGRAPHY. I. K. W. Jurisch. Salpeter und sein Ersatz. Leipzig, 1918. II. A. H. Rogers & H. R. Van Wagenen. The Chilean Nitrate Industry. III. G. Steinmann. Reisenotizen aus Chile. Neues Jahrbuch für Min. IV. Ed. Suess. The Face of the Earth. Oxford, 1906. V. Ed. Suess. La Face de la Terre. Colin et Cie., 1897. VI. James A. Doulas. Geoloical Section through the Andes of Peru and VIII. J. Brüggen. La Jeologia de la Rejion de Pica. Boletin de la Soc. X. E. W. Berry. Fossil Plants from Bolivia, etc. Proc. U. S. Nat. Museum, vol. 54, 1907, pp. 103–164 XI. Semper and Michels. Die Salpeterindustrie Chiles. Berlin, 1904. XII. F. W. Clarke. The Data of Geochemistry. U. S. Geol. Survey, Bull. 616, 1916. XIII. R. A. F. Penrose, Jr. The Nitrate Deposits of Chile. Jour. Geology, vol 18, 1910, p. I. XIV. J. T. Singewald, Jr., & B. L. Miller. The Genesis of the Chilean Nitrate Deposits. Ecox. Gao, vol. 11, 1916, pp. 193-114. XV. L. W. Strauss. The Chilean Nitrate Industry. Min. & Sci. Press, vol 102, 1914 pp. 972 and 1014 XVI Courtenay de Kalt. Origin of Nitrate. Mn, & Sci. Press, vo, 112, 19:5. p. 563 XVII. Lorenzo Smét J. T. Singewald Jr. & BL Men Discution of Nitrate Origin. Eccx. Gect, vol 12, 1957 % 4. L. Darapsky. Das Deaneet Taltal L. Sundt. El Origin del Salitre Chileno. Trabajos del Cuarto Congress Cientifico, II Seccion, Tomo I, 1911, pp. 512–520, Santiago. J. T. Singewald, Jr., & B. L. Miller. Mineral Deposits of South America, 1919, pp. 283-302; bibliography, pp. 325-347. Bibliography. Boletin de la Sociedad Nacional de Mineria. Nos. 244 and 245, June and July, 1919. Key, p. 597. CARBON RATIOS IN CARBONIFEROUS COALS OF OKLAHOMA, AND THEIR RELATION TO PETROLEUM. MYRON L. FULLER. INTRODUCTION. In other papers1 attention has been called by the writer to the great importance of the hypothesis, advanced by David White,2 that the percentage of fixed carbon in pure coal affords a measure of incipient metamorphism and a method of determining the general prospects of oil in a region in which coals occur. Notwithstanding the simplicity of the method and the definiteness of results, very little use of it has been made, only one or two of the scores of geologists with whom the writer has talked having made practical application of it in the field. This appears to be due in part to the appearance of White's discussion in a publication known to comparatively few and accessible to still fewer geologists, and in part to the extremely cautious and somewhat general character of the original statements.3 USE OF TERMS. Carbon-Ratios.-Carbon-ratio is a term used to designate the percentage of fixed carbon in pure coal. It is not the "fixed carbon" of the ordinary proximate analysis which includes both water and ash, but is the percentage of fixed carbon after water and ash are eliminated and the coal reduced to a fixed carbonvolatile matter basis. It is computed by dividing the fixed carbon 1 Bull. Geol. Soc. Am., Vol. 28, p. 649, 1917. ECONOMIC GEOLOGY, Vol. 14, No. 7, pp. 536-542, November, 1919. 2" Some Relations in Origin Between Coal and Petroleum," Wash. Acad. Sci., Vol. 6, March 16, 1915, pp. 189-212. * More specific statements are made in a subsequent paper on "Late Theories Regarding the Origin of Oil," Bull. Geol. Soc. Am., Vol. 28, pp. 727-734, September 30, 1917. of the proximate analysis by the sum of the fixed carbon and volatile matter of the same analysis. Isovolves. The term isovolve was proposed by David White as a substitute for the more complicated "isoanthracitic" of Strahn and Pollard, and is applied to the lines of equal fixed carbon percentages as determined on a pure coal basis, as outlined above. RELATION OF FIXED CARBON IN COALS TO OIL AND GAS. The writer in his paper on the carbon ratios of North Texas attempted to set forth the relationship of carbon ratios in coals to oil and gas in a precise and definite form. The conclusions are repeated in abbreviated form below. Carbon Ratios (Surface). Over 70 65-70 60-65 55-60 50-55 Under 50 Production. No oil or gas with rare exceptions. Usually only "shows" or small pockets. Commercial pools rare but oil exceptionally high Gas wells common but usually isolated rather than in pools. Principal fields of light oils and gas of the Appalachian fields. Principal fields of medium oils of Ohio-Indiana and mid-Continental fields. Fields of heavy coastal plain oils and of unconsolidated Tertiary or other formatoins. In utilizing the above table, or the more complete table in the paper on the North Texas field, it is to be borne in mind that the limits of any group are not hard and fast, but are subject to more or less variation. Analyses of the same coal may range through several points, owing to differences in laboratory manipulation, while the coals in a given region may vary a point or two, possibly more occasionally, as a result of original differences in material, changes incident to migration, composition of enclosing formation, and losses by natural distillation. For these reasons, 4" "Coals of South Wales Coal Field," p. 72. 5 ECONOMIC GEOLOGY, Vol. 14, No. 7, pp. 536-542, November, 1919. |