LESLEY, Peter, geologist, born in Philadelphia, Pennsylvania, 17 September, 1819. In early life he was Peter Leslie, Jr., and assumed the business signature J. P. Lesley, which he still retains. He was graduated at the University of Pennsylvania in 1838, and during the three following years served as assistant on the geological survey of Pennsylvania under Henry D. Rogers. In 1841 he entered the Princeton theological seminary, and in April, 1844, was licensed to preach by the presbytery of Philadelphia, but a month later went abroad and spent the winter in the University of Halle, attending the lectures of Erdmann, Leo, Tholuck, and Ulrici. On his return in the spring of 1845 he entered the employ of the American tract society in Pennsylvania, remaining for two years, and spent the winter of 1847-'8 in geological work in Boston. Subsequently for three years he had charge of the Congregational church in Milton, Massachusetts; but, his theological views changing, he left the pulpit and settled in Philadelphia, where he has since been engaged as a professional expert in geology, and in 1855-'9 was secretary of the American iron association. In 1872 he became professor of geology and mining, and also dean of the scientific faculty, in the University of Pennsylvania, ceased his teaching in 1878, and in 1886 was made professor emeritus. His geological work has included surveys of the Cape Breton coal fields in 1862-'3, numerous special examinations of coal, oil, and iron fields in the United States and Canada; and he is recognized as a chief authority in the United States on all questions connected with the coal formation of North America. Hence, on the establishment of the complete geological resurvey of Pennsylvania in 1874, he was made chief geologist in charge of the undertaking. His official duties in this capacity, involving the publication of more than seventy volumes of reports, have prevented in a great measure his personal work as a geologist; but he has published over his own name the several prefaces and notes to the reports. In 1863 he was sent to Europe by the Pennsylvania railroad company to examine methods of hardening the surface of rails and to report on the success of Bessemer's invention. He was one of the ten commissioners that were appointed by the United States senate to visit the World's fair in Paris in 1867. Professor Lesley was secretary and librarian of the American philosophical society from 1858 till 1885, and during that time prepared a catalogue of its library in three volumes (1863, 1866, and 1878). He is also a member of various other scientific societies, and was one of the original members of the National academy of sciences. In 1883 he was elected president of the American association for the advancement of science, and made his retiring address at the Ann Arbor meeting in 1885. He delivered a course of lectures before the Lowell institute, Boston, in 1865, which was subsequently published under the title of "Man's Origin and Destiny as seen from the Platform of the Sciences" (Boston and London, 1868; revised ed., 1887). Besides numerous memoirs on geological, philological, and antiquarian subjects, he has edited the "United States Railroad and Mining Register" in 1859-'62" the "Early Proceedings (1744 to 1838) of the American Philosophical Society, from the Original Records" (Philadelphia, 1885); and the "Reports of the Second Geological Survey of Pennsylvania" (1875 et seq.); and he has also published "Coal and its Topography" (Philadelphia, 1856); "The Iron Manufacturer's Guide" (1858); "Historical Sketch of Geological Explorations in Pennsylvania" (Harrisburg, 1876); and "Paul Dreifuss, his Holiday Abroad" (Boston, 1882).--His wife, Susan Inches, is the daughter of Judge Joseph Lyman, of Northampton, Massachusetts, married Professor Lesley in 1849, and has been devoted to the work of organized charities in Philadelphia. She has published "Memoirs of Mrs. Anne J. Lyman" (Cambridge, 1876; 2d ed., entitled "Recollections of My Mother," Boston, 1886).