Show Summary Details

Page of
PRINTED FROM American National Biography Online. © Oxford University Press, 2018. All Rights Reserved. Under the terms of the licence agreement, an individual user may print out a PDF of a single article in American National Biography Online for personal use (for details see Privacy Policy).

Iddings, Joseph Paxsonfree

(21 January 1857–08 September 1920)
  • H. S. Yoder Jr.

Iddings, Joseph Paxson (21 January 1857–08 September 1920), petrologist and educator, was born in Baltimore, Maryland, the son of William Penn Iddings, a merchant, and Almira Gillet. With the encouragement of his father, Iddings graduated in 1877 with a Ph.B. in civil engineering from the Sheffield Scientific School of Yale University. He spent the next year in graduate study of chemistry and mineralogy while assisting in courses in mechanical drawing and surveying. He continued his studies in geology and assaying during 1878–1879 at the Columbia School of Mines, mainly as a result of the influence of a lecture at Yale by Clarence King. During 1879–1880 Iddings studied microscopical petrography under K. H. F. Rosenbusch at Heidelberg, the principal experience that guided his career. As a result of his meeting Arnold Hague in London in the spring of 1880, Iddings returned to the United States to work at the U.S. Geological Survey.

He first worked as an assistant geologist to Hague in the Eureka, Nevada, mining district, sharing a tent with Charles D. Walcott, who eventually became director of the Geological Survey. He briefly spent some time with George F. Becker at the Virginia City, Nevada, ore deposits after a brief visit in April 1880 to the American Museum of Natural History, New York, primarily to study the collections of the Fortieth Parallel Survey on temporary deposit there until 1884. The first folio of the Geologic Atlas of the United States, the Livingstone, Montana, quadrangle, was produced by Iddings and Walter Harvey Weed in 1894. For seven field seasons (1883–1890) Iddings worked with Hague on the exploration and mapping of the geology of Yellowstone National Park. It was here that he developed most of his original, and often controversial, ideas that were to influence greatly future petrologic thinking. He concluded that the graduations of crystalline textures and mineral compositions were dependent on the physical conditions attending the consolidation of an igneous magma; phenocrysts (a term invented by Iddings in 1889 for prominent crystals in a porphyritic rock) resulted from rapid crystallization before final consolidation of a magma; volatile constituents served as mineralizing agents; and associated igneous rocks were related to a common magma. He challenged the view that granular rocks were produced only in large masses at depth. These fundamental concepts on the origin of igneous rocks were summarized in a long paper presented to the Philosophical Society of Washington in 1892. As a result of the elimination of his statutory position and reduction in funds at the Geological Survey in July 1892, Iddings resigned to accept, on 1 January 1893, at the request of Thomas C. Chamberlin at the University of Chicago, the first independent chair of petrology in the world. He had also been considered for positions at Yale, Stanford, and Johns Hopkins.

Teaching renewed his interest in the classification of igneous rocks that had arisen earlier when he translated and abridged Rosenbusch’s “Mikroskopische Physiographie der Petrographisch wichtigen Mineralien” (1888). He consulted early in 1893 with C. Whitman Cross, Louis V. Pirsson, George H. Williams, and Henry S. Washington, and, after the death of Williams, they produced in 1902 the C. I. P. W. quantitative system for classifying igneous rocks from chemical analyses expressed as ideal or normative end-member minerals, a work that had a profound influence on both field and experimental petrology. Even with the aid of his new classification of igneous rocks, Iddings did not like to teach, and his students did not consider him an effective teacher. Only two Ph.D. theses were carried out under his supervision. In the spring of 1908 he appears, on the basis of several accounts, to have been informed of the death of an aunt and of a substantial inheritance. Iddings abruptly departed from the university, and although he was granted a year’s leave of absence, he never returned. He settled at the family estate, “Riverside,” at Brinklow, Maryland.

Now free to write, lecture, and travel, Iddings produced a two-volume work titled Igneous Rocks (vol. 1, 1909; vol. 2, 1913); a series of lectures at Yale, which was published as The Problem of Volcanism (1914); and revisions to his Rock Minerals (1911). He circled the globe twice, in each direction, collecting rocks, particularly in the South Pacific Islands. Iddings was active at the Cosmos Club in Washington, D.C. (1885–1920) and in the Petrologists Club (1910–1919), which met for many years in the home of his close friend C. Whitman Cross. He gradually retired from public life, unmarried, and rented the “Grove Hill Farm,” near the family estate, in 1915 with his sister Lola LaMotte Iddings, a poet. He was a member of the Congregational church, although his grandfather, Caleb P. Iddings, was a Quaker who had been “disowned” on his marriage to a Calvinist. Iddings died at the Montgomery County, Maryland, hospital of chronic interstitial nephritis. Fittingly, his tombstone in the Woodside Cemetery of Brinklow, Maryland, is a large rock boulder.

Iddings has been described as a reserved, cultured gentleman who made lasting friendships wherever he went in the world. He was elected a foreign member of the Scientific Society of Christiania (1902) and the Geological Society of London (1904); a member of the National Academy of Sciences (1907) and the American Philosophical Society (1911); an honorary member of the Socíeté francaise de Mineralogie (1914); and a fellow of the Geological Society of America (1889, serving as vice president in 1916). Yale University gave him an honorary doctor of science in 1907. The mineral iddingsite, described initially by Iddings (1892) and now believed to consist of several phases resulting from the alteration process of iddingsization, was named in his honor by Andrew C. Lawson in 1893. He was also honored by the name of an early Cambrian trilobite, Olenellus iddingsi Walcott (1884), that was later recognized as a new genus and called Peachella iddingsi Walcott (1910). A scholarship in his name was set up at Yale University by his sister Estelle Iddings Cleveland with the residua of his estate and supplementary funds.


Letters written during Iddings’s travels to the South Pacific during 1914, and correspondence with Charles Walcott, are in the Archives of the Smithsonian Institution. His correspondence with Arthur Day, director of the Geophysical Laboratory, from 1907 to 1920, is in the archives of that laboratory. Letters to Thomas C. Chamberlin are in the archives of the Department of Geophysical Sciences, University of Chicago. Iddings’s unfinished autobiographical manuscript, “Recollections of a Petrologist,” given to C. Whitman Cross before Iddings’s death and referred to in the most extensive biography of Iddings—E. B. Mathews, “Memorial of Joseph Paxton [sic] Iddings,” Bulletin of the Geological Society of America 44 (1933): 352–74—is not among the Cross papers retained by his namesake grandson. The Mathews biography contains a detailed bibliography of Iddings’s publications. Some of the more important investigations include “On the Crystallization of Igneous Rocks,” Bulletin of the Philosophical Society of Washington 11 (1889): 67–113; “The Eruptive Rocks of Electric Peak and Sepulchre Mountain, Yellowstone National Park,” U.S. Geological Survey, Annual Report 12 (1891): 569–664; “The Origin of Igneous Rocks,” Bulletin of the Philosophical Society of Washington 12 (1892): 89–213; Microscopical Petrography of the Eruptive Rocks of the Eureka District, Nevada, U.S. Geological Survey Monograph, no. 20 (1892), pp. 335–96; “Extrusive and Intrusive Igneous Rocks as Products of Magmatic Differentiation,” Quarterly Journal of the Geological Society of London 52 (1896): 606–7; “On Rock Classification,” Journal of Geology 6 (1898): 92–111; “The Igneous Rocks of the Absaroka Range and Two Ocean Plateau and of the Outlying Portions of the Yellowstone National Park,” U.S. Geological Survey Monograph 32 (part 2, chap. 8; 1899): 269–325; “A Quantitative Chemico-mineralogical Classification and Nomenclature of Igneous Rocks” (with C. W. Cross, L. V. Pirrson, and H. S. Washington), Journal of Geology 10 (1902): 555–690; and The Isomorphism and Thermal Properties of the Feldspars. Part II. Optical Study, Carnegie Institution of Washington Publication no. 31 (1905), pp. 79–95.