Sources: NHyF
- Samuel L. Clemens to David Gray, 18 April 1874 · Elmira, N.Y · UCCL11400 NHyF
- Samuel L. Clemens to David Gray, 28 March 1875 · Hartford, Conn · UCCL11401 NHyF
- Samuel L. Clemens to David Gray, 10 April 1878 · Elmira, N.Y · UCCL11402 NHyF
- Samuel L. Clemens to David Gray, 2 June 1878 · Heidelberg, Germany · UCCL11403 NHyF
- Samuel L. Clemens to David Gray, 18 September 1879 · Elmira, N.Y · UCCL11404 NHyF
- Samuel L. Clemens to David Gray, 10 June 1880 · Hartford, Conn · UCCL11405 NHyF
- Samuel L. Clemens to David Gray, 23 September 1880 · Elmira, N.Y · UCCL11406 NHyF
- Samuel L. Clemens to Martha G. Gray, 17 November 1880 · Hartford, Conn · UCCL11407 NHyF
- Samuel L. Clemens and Olivia L. Clemens to Martha G. Gray, 26 November 1880 · Hartford, Conn · UCCL11408 NHyF
- SLC to David Gray, 9 November 1881 · Hartford, Conn · UCCL11409 NHyF
- Elihu Vedder to SLC, 20 November · UCLC50314 NHyF
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