Nine of these letters are addressed to Sir Alexander Dick of Edinburgh (1763-1768), and relate to Morgan's medical studies, his travels on the Continent, and the founding of the medical department of the College of Physicians. These are copies of originals in possession of Mrs. Dick Cunyngham, Prestonfield House, Edinburgh. In addition there are letters from Morgan to: Petrus Camper, William Smith, Samuel Vaughan, Jr.; and from Peter Collinson to Camper; Camper to Morgan; S. Vaughan Jr. to Camper; and an exchange between Christian F. Michaelis and Camper. These concern Morgan, with mentions of fossils (mastodon bones in America), natural history, comments on Franklin, Jefferson, and Angelica Kauffmann. These are from originals in the Petrus Camper Papers, on deposit (1976) at the University of Amsterdam Library.

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.