The correspondence is principally to Zaccheus Collins (1810-1840), with bills, receipts, and notes on Rafinesque vs. Parker; letters from Collins, L.A. Tarascon, Lewis C. Beck, John Torrey, and Charles W. Short (1817-1835); and miscellaneous correspondence and documents relating to Rafinesque vs. Parker, with an account of the Felician Society of Feliciana County, Illinois (1820). The writings are chiefly on botanical topics, and include notes and essays on Indians, Blacks, grapes and wine-making, banking, and speculation. Rafinesque's growing interest in Indian antiquities, linguistics, and history is apparent in letters after 1820. There is an account of Rafinesque's scientific travels in North America and southern Europe (1800-1832), and a bibliography. The botanical notes include descriptions of specimens collected by Lewis and Clark, Patrick Gass, and Henry Muhlenberg.

This is primarily a collection of letters, with some additional documents, concerning Young's interest in botany, geology, mineralogy, and natural history. There is information about Bowdoin College, where he studied under Parker Cleaveland. There is also much on the natural history of Maine, where he was the State Botanist in 1847-1849, and also on the Bangor Natural History Society. There are materials on Brazil in relation to Young's service there as the U.S. consul to Rio Grande do Sul from 1863 to 1873. There are also letters from his brother, John C. Young, and his sister, Sarah Augusta Young.

This collection includes letters from, and drafts of letters to, scientists, artists, musicians, soldiers, political figures, and court personages throughout Europe, especially Italy and France. Topics covered range from personal and social affairs to agriculture, botany, geology, natural history, coinage, museum management, politics, weights and measures, current affairs. The collection also includes four diaries, housed separately with manuscript volumes.

There is correspondence concerning geology, botany, natural history, natural selection, evolution, British science and scientists, and other scientific topics. Most of the letters are written by Lyell, with a very few items by others.

William Jacob Robbins (1890-1978, APS 1941) was a botanist and physiologist. From 1937 to 1957 he was director of the New York Botanical Garden. His research focused on culture methods of plants in relation to biochemistry and nutrition, especially on the synthetic abilities of fungi. His studies paralleled the scientific agenda of the Rockefeller Foundation, an agency with which he was closely associated for years as adviser and trustee. He was perhaps the most influential botanist in the National Academy of Sciences (NAS) during the early postwar era, and a principal participant in the plans for the global reconstruction of science. Robbins served as president of the American Philosophical Society from 1956 to 1959.