These letters are to William Hepworth Dixon, who was editor of the "Athenaeum," a journal of literature, science, the fine arts, music, and drama, from 1871 to 1900. They concern current publications and publishing expenses, Michael Faraday, astronomy, perspective, M. F. Maury, P. B. Du Chaillu, all in relation to the "Athenaeum" or letters to the editor thereof.

These are primarily letters to Gray on various aspects of natural history, with many references to collections at the British Museum of Natural History. There are numerous letters from British scientists and from European colleagues. There are letters from Americans too, such as those from Agassiz which relate to his Florida expeditions and the creation of natural history collections.

George Ord made important contributions as an ornithologist and writer but is also famous for his contempt of fellow ornithologist John James Audubon. Throughout his life he published numerous scientific articles and assisted in completing Alexander Wilson's life's work, American Ornithology; or, The Natural History of the Birds of the United States. Ord also left his mark as a member of the American Philosophical Society and as the president of the Academy of Natural Science of Philadelphia. The George Ord collection consists primarily of outgoing personal correspondence to Charles Waterton ranging from 1831 to 1866 that highlights Ord's professional as well as personal affairs, most notably his hostility toward Audubon. The collection is supplemented by correspondence of Ord's to and from various individuals regarding personal and business matters.