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.

Typed proposal, by Mason, for 'a scheme of mutual help and entertainment for conscientious university teachers of English', whereby individuals were invited to subscribe for a fee of two pounds to send and receive newssheets of items of interest from others in the profession. Undated.