Compare Letters 3, p. 363 n. 3, which dates their acquaintance from 14
1869: "Among the 'good boys' on the *Courier* was its co-editor, poet David
Gray (1836-88), who became one of Clemens's closest Buffalo friends."  In
Letters 4, the index lists several dozen page references to Gray, including
main entry at p. 102 n. 9. Clemens later recalled that Gray became an
friend through his intimacy and mine with John Hay" (L4, 292 n. 3).