This is a recording of Fowler's remembrances of Philadelphia naturalists who were affiliated with the Academy of Natural Sciences of Philadelphia, where he worked. Fowler remembers Edward D. Cope and Samuel N. Rhoads in particular.

These field diaries of this collecting trips to the American West provide detailed background information on the geology and precise position in which he uncovered fossils, as well as description of fossils, and Greek names he assigned to them. He sketched geological formations, fossils he discovered, and his conceptions of the way the animal might have appeared in life. One journal covers his trip to Paris in 1892.

This is a small but diverse collection documenting Wheatley's interests in mines and mining technology, paleontology, mineralogy, and shells. There are sketches of Wheatley's mine near Phoenixville, Pennsylvania; estimates of costs of machinery, and a list of furnace products sent to the Centennial Exposition.

This collection contains professional and personal correspondece, as well as some personal business accounts. The topics mentioned range from general ornithology to specific birds, particularly of the West Indies and South America; bird illustrations and various publications; paleontology, and zoology.

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.