Series consists of incoming and outgoing general and specific correspondence, 1856-1887, re a wide range of academic and University administrative subjects, and family correspondence, 1887-1962, after Nelles' death. Correspondents include Egerton Ryerson, J.J. Maclaren, J.G. Hodgins and Isaac Brock Aylesworth.
Despite the fact that Nelles was apparently an avid letter writer, his correspondence comprises only one and a half boxes of the collection. As Nelles explained in a letter to J.G. Hodgins, he made a practice of discarding most of the letters which he received, making exceptions only for those of great personal significance. As a result, the bulk of the surviving correspondence was preserved by chance or through the efforts of other people. The letters span the years 1846–1887; they are organized chronologically and, when the volume warrants, by correspondents such as J.G. Hodgins, Egerton Ryerson, J.J. Maclaren, and Samuel Rose. An attempt has been made to document the thrust of each letter in the file listings. Although the letters touch on a number of subjects, the main theme of the correspondence is undoubtedly the "university question". The letters outline the development of the federation concept and the responses it evoked from the university community. One can gain insight into the day-to-day activities and tensions of Victoria College, and the precarious financial position of the college emerges clearly. Letters from old college friends such as Daniel Martindale, R.C. Pitman, and J.G. Hodgins reveal Nelles' interests as well as his capacity for warm and lasting relationships.
The correspondence also includes several letters to Mrs. Nelles following her husband's death and the correspondence of Professors Nathanael Burwash and A.R. Bain regarding the Nelles Memorial Fund. In additon, there are several files of letters dated in the 1950's and 1960's which chronicle some of the research into the Nelles' family history carried out by a descendent, F.C. Gullen. A file of notes made by Gullen contains a sketch map of Mount Pleasant, a typescript of a family history, and assorted family trees. A photograph of Nelles' birthplace was transferred to the Nelles file in the Archives' photograph collection.