Cross, Charles Whitman

(b. Amherst, Massachusetts, 1 September 1854; d. Chevy Chase, Maryland, 20 April 1949)

petrology.

Cross was the son of Rev. Moses Kimball Cross and Maria Mason Cross. In 1875 Amherst College awarded him the B. S. degree; he then attended Göttingen and received the Ph.D. at Leipzig in 1880 under Ferdinand Zirkel. On his return to America, Cross joined the U. S. Geological Survey, which he served for forty-five years. He received an honorary D. Sc. degree from Amherst College in 1925. He married Virginia Stevens and had one son, Richard Stevens Cross.

Cross’s accurate field investigations, which were carried out primarily in Colorado, constitute his greatest contribution to geology. He and his assistants mapped the rock formations of seven quadrangles in the rugged terrain of the San Juan Mountains, covering over 1,800 square miles on foot and horseback. The region includes the mining camps of Ouray, Telluride, Silverton, Rico, Needle Mountains, Lake City, and La Plata. About 1,000 square miles were mapped geologically in the Pikes Peak area, which includes the Cripple Creek mining camp, and another 1,000 square miles in the Apishapa quadrangle. In addition to the broad aspects of the rocks as geologic units, Cross tended to the collection, description, and classification of the rocks from these areas and was concerned with the processes that had produced them. Other notable petrologic studies include those of the potash-rich rocks of the Leucite Hills, Wyoming, the first leucite-bearing rocks discovered on the American continent; and the lavas of the Hawaiian Islands, which were found to have a considerable range of composition. Cross discovered an occurrence of trachyte on the island of Hawaii, previously considered generally basaltic in composition.

In addition to his vast fieldwork, Cross collaborated with Joseph P. Iddings, Louis V. Pirsson, and Henry S. Washington in devising a quantitative chemicomineralogical classification and nomenclature of igneous rocks, commonly referred to as the C. I. P.W. system. From the chemical analysis of a rock, they calculated a “norm” made up of simple theoretical minerals that may be taken to represent, for the most part, the end members of the minerals actually occurring in the igneous rocks. This ingenious scheme, still widely used today, has not only led to an appreciation of the chemical composition of natural igneous rocks but has also served as the basis of much of the experimental investigation of those rocks.

Cross was among the group of geologists who helped persuade the Carnegie Institution of Washington to establish a laboratory (the Geophysical Laboratory since 1906) for the experimental investigation of rocks at high pressures and temperatures. He was a charter member of the Petrologists’ Club (organized 1910) along with Bancroft, Bastin, Johannsen, Knopf, Larsen, Lindgren, Paige, and Schaller, among others. The organizational meeting and numerous successive meetings, at which many major petrological concepts were first discussed, took place in his home. As a member of the National Academy of Sciences (elected 1908), Cross served in other ways to advance the progress of geology—for example, by taking an active part in the organization of the National Research Council. He was a member of the Geological Society of America and served as its president in 1918.

Retirement in 1925 did not mark the end of Cross’s scientific career; his systematic methods were trasferred with equal vigor to the cultivation of roses. He developed new varieties, some of which became available commercially. The outstanding varieties include “Chevy Chase,” “Mrs. Whitman Cross,” and “Hon. Lady Lindsay.” His successes also extended to investment and finance; however, there is no record of his achievements in golf, his chief recreation.

BIBLIOGRAPHY

U.S. Geological Survey folios of Colorado for which Cross was responsible are no. 7, Pikes Peak Sheet (1894); no. 57, Telluride Quadrangle (1899), with C. W. Purington; no. 60, La Plata Quadrangle (1899), with A. C. Spencer and C. W. Purington; no. 120, Silverton Quadrangle (1905), with E. Howe and F. L. Ransome; no. 130, Rico Quadrangle (1905), with F. L. Ransome; no. 131, Needles Mountain Quadrangle (1905), with E. Howe, J. D. Irving, and W. H. Emmonds; no. 153, Ouray Quadrangle (1907), with E. Howe and J. D. Irving; no. 171, Engineer Mountain Quadrangle (1910), with A. D. Hole; and no. 186, Apishapa Quadrangle (1912), with G. W. Stose.

His publications on regional petrology include “Igneous Rocks of the Leucite Hills and Pilot Butte, Wyoming,” in American Journal of Science, 4th ser., 4 (1897), 115–141; Lavas of Hawaii and Their Relations, U.S. Geological Survey Professional Paper no. 88 (Washington, D.C., 1915); and Geology and Petrology of the San Juan Region of South-western Colorado, U.S. Geological Survey Professional Paper no. 258 (Washington, D.D.), written with E. S. Larsen, Jr.

On the C. I. P. W. system, see “A Quantitative Chemicomineralogical Classification and Nomenclature of Igneous Rocks,” in Journal of Geology, 10 (1902), 555–690, with J. P. Iddings, L. V. Pirsson, and H. S. Washington; Quantitative Classification of Igneous Rocks, Based on Chemical and Mineral Characters, With Systematic Nomenclature (Chicago, 1903), written with Iddings, Pirsson, and Washington; and “The Natural Classification of Igneous Rocks,” in Quarterly Journal of the Geological Society of London, 66 (1910), 470–506.

H. S. Yoder, Jr.