Mentioned in these letters are personal affairs, experiments, Babbage's calculating machine, and his "Bridgewater Treatise," second edition.

A product of the distinctive culture of reform in antebellum Philadelphia, William Parker Foulke was the scion of the old elite who put a conservative stamp on social change. Trained as an attorney, Foulke spent much of his adult life engaging his deep amateur interest in natural history and mental philosophy and devoting himself to a variety of civic and philanthropic causes, including the colonization of formerly enslaved persons, penal reform, and cultural institutions in his native Philadelphia. The Foulke Papers are the product of the diverse social and intellectual interests of the Philadelphia attorney and philanthropist William Parker Foulke. Consisting primarily of correspondence, notes, and essays, the collection touches on Foulke's many interests. The collection includes numerous lectures delivered by Foulke along with material on the Lancaster County Prison, New York Prison Association, and the Philadelphia Society For Alleviating the Miseries of Public Prisons; notebooks concerning prisons and prisoners, including a 1846-1852 diary, and a listing of prisoners, their race, age, crime, sentence, and observations; a diary concerning the American Colonization Society (1852); a copy of an arctic diary (1853-1854) by John Wall Wilson, in the hand of Isaac Israel Hayes, which recounts much of the journey aboard the brig Advance, commanded by Elisha Kent Kane. There is also a list of buildings (1820-1841) designed by John Haviland, and material on the American Academy of Music, Philadelphia.

After a brief career in the Congregational church, J. Peter Lesley (1819-1903) left the ministry in 1852 to work full-time as a geologist. Having gained experience in structural geology and stratigraphy with the First Pennsylvania Geological Survey (1836-1842), Lesley became an expert in the geology of coal, working for the Pennsylvania Railroad and other corporations and conducting some of the first systematic studies of the state's hydrocarbon resources. A long-time professor at the University of Pennsylvania, he was elected to the APS in 1856, serving variously as its librarian, secretary, and vice president, and he was selected as Director of the Second Pennsylvania Geological Survey (1875-1889). The Lesley Papers include letters to and from Peter Lesley and his wife, Susan on geology, coal and iron mining, abolition, educational reform, organized charity, and Unitarianism. The collection offers important insight into academic and applied geology in late 19th century Pennsylvania, the development of the coal and iron industries, as well as into the Lesleys' progressive social and intellectual milieu. It is divided into three series: Lesley's general correspondence, his correspondence with his brother Joseph, and microfilms of Lesley's research notes.