Iddings, Joseph Paxson

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Iddings, Joseph Paxson

(b, Baltimore, Maryland, 21 January 1857; d. Brinklow, Maryland, 8 September 1920)


Iddings was the son of William Penn Iddings and the former Almira Gillet. His father encouraged him to become a mining engineer, and he graduated from the Sheffield Scientific School of Yale University in 1877. Following a year as an instructor at Yale, he spent a year at the School of Mines, Columbia University, eventually turning to geology as a result of the influence of Clarence King. During 1879-1880 Iddings studied at Heidelberg under K. H. F. Rosenbusch, an experience which led to his career as a petrographer. On his return to America in 1880 he joined the U.S. Geological Survey, at about the same time as C. Whitman Cross, and served through 1892. He then joined the new department of geology at the University of Chicago, leaving abruptly in 1908 when he learned of the death of an aunt; an inheritance was presumed to be involved. The remainder of his bachelor life was spent collecting, writing, lecturing, traveling, conversing with his scientific friends in Washington, or residing at his ancestral home in Maryland.

One of the early few to study thin rock sections by means of the microscope, Iddings became one of the foremost petrographers of his time through his detailed, worldwide collecting and study of igneous rocks. His early broad surveys of rocks were done mainly in conjunction with fieldworkers such as Arnold Hague, C. D. Walcott, and G. F. Becker. Participation in the exploration and mapping of the geology of Yellowstone National Park was the most rewarding of Iddings’ field studies. He concluded from these studies that the textural and chemical variation of igneous rocks depends on the variety of physical conditions imposed by the geological environment; that the consanguinity of some igneous rocks can be attributed to descent form a common parental magma; that mineralogical and structural variations were due largely to the rate of cooling of the magma; and that volatile constituents played a special role in rock magmas. His physicochemical approach to rocks, still valid today, greatly influenced the Carnegie Institution of Washington in the establishment of the Geophysical Laboratory as well as the course of petrology.

Iddings’ teaching duties led to his need for a satisfactory classification of rocks. He enlisted the help of his friends C. W. Cross, L. V. Pirsson, G. H. Williams, and later, on Williams’ death, H. S. Washington. They collaborated in revising rock nomenclature and expressing the compositional variations among rocks on a quantitative basis. The widely used normative method of calculating simple theoretical minerals from a chemical analysis of a rock is referred to, after its authors (alphabetically arranged), as the C.I.P.W. system. This classification served as the basis for a unique and original two-volume work, the first volume dealing with the physical chemistry of magmas and the second, a compilation of the geographic distribution of igneous rocks and the related problem of petrographic provinces.

Iddings’ course of Silliman lectures at Yale in 1914 was published as The Problem of Volcanism. This honor was preceded by election to the National Academy of Sciences in 1907, honorary membership in the Société Française de Minéralogie in 1914, and an honorary D.Sc. from Yale (1907). Iddings was described as a very reserved and shy man for a world traveler, yet possessing personal charm, broad culture, and a poetic view of his surroundings—whether they were the rock sections of his profession, the butterflies of his hobby, or the landscapes of his travels.


I. Original Works. Iddings’ U.S. Geological Survey publications are On the Development of Crystallization in the Igneous Rocks of Washoe, Nevada, With Notes on the Geology of the District, Bulletin no. 17 (Washington, D.C., 1885), written with A. Hague; a description of rocks in J. S. Diller, The Educational Series of Rock Specimens, Bulletin no. 150 (Washington, D.C., 1898), passim; “Microscopical Petrography of the Eruptive Rocks of the Eureka District, Nevada,” app. B of Arnold Hague, Geology of the Eureka District, Nevada, Monograph no. 20 (Washington, D.C., 1892), pp. 337-404; and the following articles in monograph no. 32, Geology of Yellowstone National Park, Part II (Washington, D.C., 1899): “Descriptive Geology of the Gallatin Mountains,” pp. 1-59, written with W. A. Weed; “The Intrusive Rocks of the Gallatin Mountains,” pp. 60-88; “The Igneous Rocks of Electric Peak and Sepulchre Mountain, Yellowstone National Park,” pp. 89-148; “Descriptive Geology of the Northern End of the Teton Range, Yellowstone National Park,” pp. 149-164, written with W. H. Weed; “The Dissected Volcano of Crandall Basin, Wyoming,” pp. 215-268; and “The Igneous Rocks of the Absaroka Range, Yellowstone National Park,” pp. 269-439.

Journal articles include “Notes on the Change of Electric Conductivity Observed in Rock Magmas of Different Composition on Passing From Liquid to Solid,” in American Journal of Science, 3rd ser., 44 (1892), 242-249, written with Carl Barus; “The Origin of Igneous Rocks,” in Bulletin of the Philosophical Society of Washington, 12 (1897), 89-216; “Chemical and Mineral Relationships in Igneous Rocks,” in Journal of Geology, 6 (1898), 219-237; “A Quantitative Chemico-Mineralogical Classification and Nomenclature of Igneous Rocks,” ibid., 10 (1902), 555-690, written with C. W. Cross, L. V. Pirsson, and H. S. Washington;“The Isomorphism and Thermal Properties of the Feldspars. Part II. Optical study,” in Publications. Carnegie Institution of Washington,31 (1905), 77-95, written with A. L. Day and E. T. Allen; “The Texture of Igneous Rocks,” in Journal of Geology, 14 (1906), 692-707, written with C. W. Cross, L. V. Pirsson, and H. S. Washington; and “Some Examples of Magmatic Differentiation and Their Bearing on the Problem of Petrographical Provinces,” in Compters rendus. XIIe session du Congres geologique international (Toronto, 1914), pp. 209-228.

Iddings’ books are Quantitative Classification of Igneous Rocks, Based on Chemical and Mineral Characters, With Systematic Nomenclature (Chicago, 1903); Rock Minerals, Their Chemical and Physical Charters and Their Determination in Thin Sections (New York, 1906); Igneous Rocks: I, Composition, Texture, and Classification (New York, 1909), and II, Description and Occurrence (New York, 1913); and The Problem of Volcanism (New Haven, 1914).

II. Secondary Literature. On Iddings and his work, see “Memorial of Joseph Paxson Iddings, “in Bulletin of the Geological Society of America, 44 (1933), 352-374.

H. S. Yoder, Jr.