Sub-sub-series consists of eight indexes to correspondence received in the Canal Branch from superintendents and engineers in charge of canals or canal works, officials in the Department of Railways and Canals, other government departments and some individuals. The entries are arranged in chronological order under the appropriate name, subject or department. The following information is recorded: date of the correspondence, subject, subject number, letter number and a brief synopsis. This information allows one to refer to Vols. 1161-1255 of the journals for a more detailed synopsis of the correspondence.
The Special Indexes are useful for checking at a glance all the correspondence received in the branch from a specific individual or department. It should be noted that correspondence indexed in these volumes is not indexed in the General Indexes. Researchers should also be aware that Vol. 1267 begins in January 1879, although Railways and Canals did not become operational until October of that year; for this reason, Vol. 1267 includes references to correspondence on matters that were under the jurisdiction of Public Works.
Volumes 1794-1795 and 1816-1817, although slightly different in format than earlier volumes, provide essentially the same information. However, when the journal method of recording correspondence was abandoned in 1906 in favour of a numbered subject file system, the change was reflected in these four indexes.