The archive comprises mainly correspondence addressed to Sir Walter and his first wife Pauline Lady Trevelyan nee Paulina Jermyn. The letters reflect the couple's interests in natural history, botany, geology, antiquities, travel, temperance, phrenology, art and literature, and include examples from many well known contemporaries.

There is also material relating to the history of the Trevelyan family, accumulated during Walter and Charles Edward Trevelyan's preparation of 'The Trevelyan Papers' for publication.

The archive also features diaries and journals, sketchbooks, notes for speeches and scrapbooks. There is material relating to the North East of England, including proposed railways, Tyne crossings at Hexham and decoration of the Great Hall at Wallington.

The Wallis Collection contains books on mathematics and maths education and includes works by Robert Record (the man who introduced the = symbol), such as The grounde of artes: teaching the perfecte worke and practise of arithmetike (1582) and works by and about Isaac Newton, such as Newton's Principia in its first American edition (1846).

The books were formerly owned by Peter Wallis (1918-1992), a lecturer in the School of Education. There are almanacs, works on algebra and geometry, school text books, works on astronomy including J.F.W. Herschel's Astronomy (1835), guides to measuring, book-keeping, ready reckoners, treatises, Euclid's Elements and manuals.