The Hall, Trevor mss., 1974-1979, consists of letters from bookman and author Percival Horace Muir, 1894-1979, to historian and writer Trevor Henry Hall, 1910-1991. The discussions are primarily about matters bibliographic, in particular the Rev. F.O. Morris's book, commonly referred to as "County Seats" (published by Longman's in 1864 in parts), along with queries regarding the location of his papers; Muir and Hall's collaboration on Some Printers & Publishers of Conjuring Books and other Ephemera 1800-1850 (Leeds: Elmete Press, 1976); and Sherlockiana. Regarding the latter topic, Muir's letter in late December 1975 comments on the recently published Seven Per Cent Solution (London: Hodder & Stoughton, 1975), describing it as "preposterous" and "fiddle-faddle indeed." Then in mid-January, he sends six pages of discussion of the book, pointing out all the areas in which it is "preposterous." These notes and observations were later used by Hall in one of the essays, "Sherlock Holmes and Sigmund Freud," in his book Sherlock Holmes and His Creator (London: Duckworth, 1978). Other topics include domestic and personal matters, Muir's interests in Goethe, children's books and juvenilia, and Ian Fleming and Printing and the Mind of Man.

There are also a few carbon copies of letters by Hall, chiefly to individuals and institutions seeking information about the Rev. F.O. Morris's papers on Muir's behalf and an annotated typed transcript of the correspondence prepared by Granville Cook and accompanied by a letter to Cook from Anthony Rota, August 1984, commenting on both the transcript and possibilities of publication. A typed carbon copy of a letter, November 2, 1992, from Cook to an unknown book dealer inquiring about the availability of Trevor Hall's publications completes the collection.