There is business correspondence, 1792-1800, with letters from among others Alexander Mackenzie, Joseph Frobisher, Alexander Henry, Simon Fraser and Roderick Mackenzie. There are also minutes and resolutions of the Executors of McTavish in a bound volume; and a contemporary copy of the minutes of the executors of his will, 1805.

The Hellmuth Wolff Organ Collection consists primarily of organ plans, pamphlets, photographs, books and periodicals, and personal correspondence. The majority of these documents are associated with or represent one of the fifty organs in Wolff’s opus. In addition to depicting Wolff’s instruments, the collection of organ plans also includes Wolff’s drawings for proposed but not-constructed organs, plans by other organ builders, and plans drawn by Wolff that are based on historical models and treatises by writers such as Dom Bédos. Of the photographs, most are associated with specific Wolff organ projects and represent a span date of the late 1960s to the early 2000s. Also in the photograph collection are images of historical organs in Europe, which Wolff presumably used in modelling and designing several of his instruments, as well as images associated with other organ projects by builders such as Casavant Frères, Karl Wilhelm, and Rieger, all of whom Wolff worked with before establishing his own workshop in Laval. The collection of pamphlets includes programs, program notes, and concert series information for several of the Recitals and concerts performed on Wolff’s instruments. Of the periodicals and books, titles include The American Organist, Choir & Organ, and Orgelforum. Also in the collection are several three-dimensional models, or maquettes, of Wolff organs.

The collection consists of autographed signed letters from multiple senders, representing authors, artists, politicians, and other figures from Canada and Europe. The letters were accumulated by the Rare Books and Special Collections unit of the McGill Library over many years and assembled into the collection.

Letters and diaries, including typescript transcriptions with photographs, newspaper clippings and ephemera.

Consists of an English translation of a letter to the Marquis de la Jonquière written by Antoine-Louis Rouillé, comte de Jouy, secretary of state for the French Navy, at Versailles, dated 28 February 1750. The letter discusses an immediate release of prisoners of war taken during conflicts between the French and British colonies. It also includes a mention of Indigenous allies of England and France, and Indigenous people captured during the conflicts: "the Indian Prisoners among the two Nations be likewise released, but after all the French and English Prisoners are released" The letter also includes the name of examiner Josiah Willard, secretary of the province of Massachusetts-Bay.