Sources: NHyF
- Samuel L. Clemens to David Gray, 18 April 1874 · Elmira, N.Y · UCCL11400
- Samuel L. Clemens to David Gray, 28 March 1875 · Hartford, Conn · UCCL11401
- Samuel L. Clemens to David Gray, 10 April 1878 · Elmira, N.Y · UCCL11402
- Samuel L. Clemens to David Gray, 2 June 1878 · Heidelberg, Germany · UCCL11403
- Samuel L. Clemens to David Gray, 18 September 1879 · Elmira, N.Y · UCCL11404
- Samuel L. Clemens to David Gray, 10 June 1880 · Hartford, Conn · UCCL11405
- Samuel L. Clemens to David Gray, 23 September 1880 · Elmira, N.Y · UCCL11406
- Samuel L. Clemens to Martha G. Gray, 17 November 1880 · Hartford, Conn · UCCL11407
- Samuel L. Clemens and Olivia L. Clemens to Martha G. Gray, 26 November 1880 · Hartford, Conn · UCCL11408
- SLC to David Gray, 9 November 1881 · Hartford, Conn · UCCL11409
- OLC to Martha G. Gray, 9 May 1882 · Hartford, Conn · UCCL12515
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