The collection is comprised of a total of 75 letters. Nos 1-54 are comprised of letters from Fitzroy to his father, his brother George Fitzroy, and his sisters Emily Fitzroy and Frances Rice Trevor, 1816-1843, including some correspondence between his siblings. They include long descriptions of topography, local events and people, naval matters, and progress of the survey. Many were written from ships and ports of call in the Mediterranean and South America, including nos 39-52, written by Fitzroy whilst commanding H.M.S. 'Beagle'. Nos 55-70 consist of correspondence from 1852 exchanged between Fitzroy, his aunt Frances Anne, Marchioness of Londonderry (wife of Fitzroy's maternal uncle, the 3rd Marquis), and his brother-in-law Lord Dynevor, regarding the proposed adoption of Fitzroy's daughter Emily by Lady Londonderry following the death of Fitzroy's first wife and Lord Dynevor's failed attempts to mediate between Fitzroy and the Marchioness. The remaining items, nos 71-75, are miscellanea, undated letters and covers.