Sources: C4
- Samuel L. Clemens to Elizabeth W. Smith, 13? October 1859 · St. Louis, Mo · UCCL00021 C4
- Samuel L. Clemens to John McComb, 8 June 1867 · New York, N.Y · UCCL00137 C4
- Samuel L. Clemens to Elisha Bliss, Jr., 4 July 1870 · Elmira, N.Y · UCCL00486 C4, CU-MARK
- Samuel L. Clemens to the Staff of the Hartford Courant, 19 October 1875 · Hartford, Conn · UCCL01271 C4
- Samuel L. Clemens to Henry Nason Kinney, 21 or 22 March 1876 · Hartford, Conn · UCCL00468 C4
- Samuel L. Clemens to Unidentified, December 1880 · Hartford, Conn · UCCL01862 C4
- SLC to C. L. Fleck, 6 February 1883 · Hartford, Conn · UCCL02343 C4
- SLC to Rebecca P. Boas, 9 January 1885 · St. Louis, Mo · UCCL03108 C4
- SLC to Robert U. Johnson, 6 July 1885 · Elmira, N.Y · UCCL03252 C4
- SLC to Richard Watson Gilder, 17 March 1887 · Hartford, Conn · UCCL03542 C4
- SLC to Annie A. Fields, 17 March 1887 · Hartford, Conn · UCCL03543 C4
- SLC to Katharine Foote, 16 January 1891 · Washington, D.C · UCCL04160 C4
- SLC to Chatto & Windus, 27 March 1892 · Rome, Italy · UCCL04279 C4
- SLC to Unidentified, June 1893 · Unknown place · UCCL09302 C4
- SLC to Dr. Good, 25 June 1894 · La Bourboule, France · UCCL04746 C4
- SLC to Henry Loomis Nelson, 12 February 1895 · Paris, France · UCCL04842 C4
- SLC to Thomas Jewell Bennett, 28 January 1896 · Bombay, India · UCCL05014 C4
- SLC to Francis E. Bliss, 21 October 1896 · London, England · UCCL05134 C4
- SLC to Gertrude Darrall, 23 February 1897 · London, England · UCCL05179 C4
- SLC to Chatto & Windus, 21 August 1897 · Weggis, Switzerland · UCCL11982 C4
- SLC to C. F. Moberly Bell, 3 March 1900 · London, England · UCCL05768 C4
- SLC to Unidentified, 1 December 1900 · New York, N.Y · UCCL09265 C4
- SLC to C. F. Moberly Bell, 26 August 1901 · Saranac Lake, N.Y · UCCL06118 C4
- SLC to Unidentified, 23 March 1903 · Riverdale, N.Y · UCCL06608 C4
- SLC to Beatrice M. Benjamin, 18 September 1903 · Elmira, N.Y · UCCL06726 C4
- SLC to Unidentified, October 1905 · Unknown place · UCCL09374 C4
- SLC to Katy Murray, 6 April 1907 · New York, N.Y · UCCL09262 C4
- SLC to Katy Murray, 1 September 1907 · Tuxedo Park, N.Y · UCCL09255 C4
- SLC to Joseph T. Goodman, 30 July 1908 · Redding, Conn · UCCL08064 C4
- SLC to George B. M. Harvey, 30 July 1908 · Redding, Conn · UCCL08065 C4
- SLC to Clara L. Clemens, 30 July 1908 · Redding, Conn · UCCL08066 C4
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