Cal, this is an interesting question. I think there is circumstantial
evidence, at least, but I would not restrict this to the South, by any
means.?Sam's trip up the Mississippi in 1882 and his visit there at Cable's
with Joel Chandler Harris; Cable's prior (June of 1881) trip east to inspect
abuses at the Boston city Jail and the state prison at Concord, as well as
the insane asylum at Hartford; Cable's subsequent activism in prison reform,
both in New Orleans and nationally; Cable's talk on prison reform, Mar. 26,
1883 before the Congretational Club in New York?(which just so happens was
the exact day that Sam telegrammed Cable to verify his upcoming "test"
lecture on "Creole Women" at Unity Hall in Hartford. Sam was grooming Cable
for the platform circuit.) And, of course, Cable's later "Freedman in
Equity" article, together with his growing acclaim (and controversy which
Sam didn't seem to want any part of) on the "Twins of Genius" tour of Nov.
5, 1884-Feb. 28, 1885. Sam!
  took up the unfinished _Huck Finn_ in the Summer of 1883, and wrote his
family of his "booming" productivity. Is it coincidence that this renewed
enthusiasm followed his trip west and his interaction with Cable, Harris,
and others? Perhaps it's more a question of impulse and motivation rather
than one of influence. If anything, Cable was more influenced in his writing
than vice versa. And Huck Finn certainly wasn't?the product of one trip up
the river at age 47.

Questions of influence are often murky, but the two men interacted quite a
lot even before the 84-5 reading tour. Clemens would have been fully aware
of Cable's activism and involvement in both prison reform and the plight of
ex-slaves. Cable may have added some aspects for Sam to Huck Finn, who
knows?? I recommend Arlin Turner's excellent 1956 bio of Cable as well as
the 1928 collection of his letters by his daughter, Lucy Bikle. And of
course, for comparing dates and events when both men interacted, you might
try _Mark Twain Day By Day_ 2008, now within days of shipment.?

David H Fears