The unit consists of notes and printed material relating to Welsh topography and history, 1928-1997, nature diaries, 1935-1998, field notebooks, 1952-1994, personal diaries, 1994-1998, notes and printed matter relating to Henry Thoreau, 1943-1999, and other naturalists, 1935-1996, correspondence, [c.1938]-2016, and travel records, 1947-1994.