The series consists primarily of incoming correspondence to various administrative units of the Natural History Society. This includes letters to the Recording Secretary, the Corresponding Secretary, the Chairman, the Librarian (dealing largely with book binding costs), the Chairman, the Editor of the Canadian Record of Science (primarily acknowledging receipt of the journal), and the Museum Curator. While most of the series consists of loose documents, it also contains two “Letter Books,” which have indexes of whom letters were sent by or to. These letters are highly administrative in nature, dealing with the daily operations of the Society and not the personal correspondence of its members.

The letters have substantial gaps between 1872-1878, 1881-1884, and in 1895. Many of the loose letters were donated to the Blacker-Wood Collection bundled together and they have been preserved together. However, many of the other loose letters were sorted by year by the archivist or librarian who originally processed them.

Notable Natural History Society members and other prominent people in these files include:
J.F. Whiteaves (non-member)
The Governor General of Canada (non-member)
David R. McCord (non-member)
Sir John William Dawson, as President
Professor David P. Penhallow, as Committee Chairman
Charles Robb, Librarian
E. J. Chambers, Librarian
R. Lachlan, Secretary