Assistant in physics, Yale, 1886-1888. Excavations in Greece, 1889-1894. Assistant in mineralogy, Yale, 1895-1896.
Geological, volc., petrol. investigations in Greece, Asia Minor, Italy, Spain, Brazil, Hawaiian Islands, and United States, and chemical study of igneous rocks and minerals. Consultant mining geologist, 1906-1912. Board of managers Geological Survey New Jersey, 1909-1914.
With Geophysical Laboratory, Carnegie Institution of Washington, since 1912. Chemical associate and scientific attache American Embassy, Rome, 1918-1919. Vice chairman of the section volcanology, International Geophysical Union.
Chairman American Geophysical Union, 1927-1929.
Author: Chemical Analyses of Igneous Rocks, 1903, 1917. Manual of the Chemical Analysis of Igneous Rocks, 1904. The Roman Comagmatic Region, 1906.
Joint Author: Quantitative Classification of Igneous Rocks. 1903. Contributor of articles on petrol., mineral, and archæol. subjects in scientific journals, 1887—.