Louis Valentine Pirsson

Louis Valentine Pirsson (born Nov. 3, 1860, Fordham, N.Y.—died Dec. 8, 1919, New Haven, Conn.) was a geologist whose studies of the igneous rocks of Montana revealed many previously unknown varieties. In 1889 he served as an assistant with a U.S. Geological Survey party in Yellowstone Park and later in Montana. He joined the faculty of Yale University in 1892 and became professor of physical geology in 1897. In Quantitative Classification of Igneous Rocks (1903),...