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.

This is a small collection of notebooks and photograph albums which belonged to John William Heslop Harrison (1881-1967), at one time Professor of Botany at Newcastle University. The notebooks contain notes on plant biology, pollination and plant genetics while the albums include photographs of Iraq, dated 1938-1941. The collection also includes Proceedings of the University of Durham Philosophical Society 1955-1956 in various stages of editing.

This collection of illustrations by local artist Thomas Hair (c.1810-1875) depicts the mining industry and the coal trade in the North East in the nineteenth century. The illustrations are based on Hair's watercolours on the same topic. The illustrations in the collection highlight numerous aspects of the region's mining heritage, including collieries, machinery, and river trade scenes. Many of the illustrations also show the everyday workings of the industry and those involved in it.