Many of the letters were originally addressed to Thomas; others were address to his brothers John (of Newcastle) and George (of London), to his father Thomas, to colleagues such as George Grey (of Newcastle), George Cuthbertson (of Newcastle), Henry Collingwood Selby (Clerk of the Peace for Middlesex), to Thomas and William Lowes of Ridley all (Northumberland), or to Louis Dutens (secretary to the Duke of Northumberland). A number of letters now bear no superscription.

The Davidsons were often engaged in political campaigns. The Dundas family, or Dundas connections, appear fairly frequently, as does the Eldon estate. Section M of the collection in particular contains an affecting series of letters by Mrs. E. Dundas, the widow of a captain in the East India Company; other East India Company personnel also appear in the collection. Many of the letters are trivial social, legal, or political notes.

Letters are generally 1-2 pages long, often with original address and seal, occasionally stamped by the post office.