Sources: MoCgS
- Samuel L. Clemens to James Redpath, 26 January 1870 · Elmira, N.Y · UCCL00417
- Samuel L. Clemens to Jacob H. Burrough, 1 November 1876 · Hartford, Conn · UCCL01384
- Samuel L. Clemens to William A. Wood, 6 April 1880 · Hartford, Conn · UCCL12917
- SLC to Unidentified, 27 October 1897 · Vienna, Austria · UCCL12918
- SLC to Frank E. Burrough, 15 December 1900 · New York, N.Y · UCCL05932
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