These are letters of William Hewson, Mary Stevenson Hewson, and Thomas Tickell Hewson, chiefly to members of the family on personal affairs. There are also a transcript of a draft of William Hewson's account of his quarrel with Dr. William Hunter and a letter from Barbeu Du Bourg to Mary Stevenson Hewson.

The correspondence (1869-1883) is primarily routine business, i.e. navy orders and letters of recommendation, and also includes some personal letters. In addition, there are several notebooks and diaries, including notes from Pennsylvania Hospital clinical lectures, 1867-1869 (2 v.); diaries, 1865-1875 (7 v.); a volume of poetry; and general study notes. There is also early material (1745-1813) on the Cassin family, including a letter of indenture dated 1758.

This collection includes letters, diaries, notebooks, and early photographs, relating primarily to the Wister family of Germantown and Philadelphia. Much of the correspondence concerns domestic news and consists of letters from or to Sarah Wister. These include interesting observations on Germantown and Philadelphia society from other families as well, such as the Bayntons and Bullocks. There are numerous letters from various Wisters, including Casper, Charles Jones, Elizabeth (including a journal of a trip to Bristol, 1783), Hannah, John, Owen Jones, and others. There is also poetry by Sarah.

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.