Consists mainly of letters to Hart from a variety of correspondents, including school and college teachers and administrators, clergymen, and authors. Many letters provide biographical and bibliographical information on authors, including authors of religious works, for a book Hart was compiling on American literature, probably his Manual of American Literature (Philadelphia, 1873). Also included is considerable correspondence from fellow editors evaluating poems submitted to Sartain's Union Magazine. Other letters discuss matters of school or college administration, including student admissions and employment openings for teachers; evaluations of recently published books and articles on a variety of subjects, including Hart's own publications; pedagogical theory; and church history.

Correspondents include Henry M. Alexander, George Henry Boker, Frederika Bremer, Hiram Corson, Erastus Wollcott Ellsworth, Caroline Chesebro, Sarah Josepha Buell Hale, John Henry Hopkins, Jr., Mary Botham Howitt, William Henry Hurlburt, Margaret Junkin, Daniel Parrish Kidder, James R. Gilmore (pseudonym: Edmund Kirke), Caroline Matilda Stansbury Kirkland, Messrs. Sartain & Co., Chloe Lankton, John Malam, Edith May, Joseph Parker Norris, William Henry Odenheimer, Lydia Howard Sigourney, Anna Bartlett Warner, Moses Coit Tyler, Richard Grant White, and Mark Twain.