LEHMANN, JOHANN GOTTLOB

born Aug. 4, 1719, Langenhennersdorf, near Pirna, Saxony died Jan. 22, 1767, St. Petersburg, Russia German geologist who contributed to the development of stratigraphy, the scientific study of order and sequence in bedded sedimentary rocks. Lehmann received his M.D. from the University of Wittenberg in 1741 and established a medical practice in Dresden. In Saxony he discovered his real field of interest, mines and mining. His publications on ore deposits and their chemical composition won for him, in 1750, an official commission by the Royal Prussian Academy of Sciences in Berlin to study mining procedures in the Prussian provinces. His explanation of the origin of mineral deposits in specific strata was summarized in the first geologic profile, published in 1756. He recognized that rocks do not fall in haphazard position but rather form in historical sequence; this principle serves as the foundation of modern stratigraphy. The Freiberg Bergakademie, a technical research institute, was founded in 1765 at Lehmann's urging. Lehmann was invited to St. Petersburg by the Imperial Academy of Sciences; in 1761 he became professor of chemistry at the university there and director of the academy's natural-history collection. His investigations in Russia became the model for geologic explorations carried out after his early death.