The collection consists primarily of correspondence on natural history topics between scientists and natural historians. Letters are sometimes accompanied by journal articles.

Figures with significant correspondence within the collection include: Casey Albert Wood, Henry Mousley, Robert Ridgway, and Bowdler Sharpe.

The fonds contains correspondence related to the Osler Library and its holdings with people such as Maude Abbott, Edward Archibald, William B. Bean, Edward Horton Bensley, Archibald Malloch, Casey Wood, as well as John Farquhar Fulton, Keeper of the Medical History Collections at Yale University's library; the fonds also contains a typescript of talks by W.W. Francis (titled "Showman's Patter") about books and other items held in the Osler Library.