The collection consists of an extensive series of letters from F. R. Leavis, 1935-63, before and after his time working with Mason at Downing College; letters from Q. D. Leavis to Mason, 1943-7; lecture notes from Mason's period at Exeter University and as F. R. Leavis Lecturer at the English Faculty in Cambridge, 1965-78; and other academic papers such as drafts for articles etc. Annotations on lecture notes and draft essays are thought to be Mason's own.