Having found no reference to a Ballarat Fly, outside of fly-fishing in
Ballarat, I remain curious as to where Mark Twain came up with that
name for the railway known as the Napier Express.  Are there any known
Twain scholars in New Zealand that might have a clue?  Twain refers to
it both as the "Ballarat Fly" and "The Fly" in the first paragraph of
chapter 35.
-- 
 There are more things in heaven and earth, Horatio, than are dreamt of
                          in your philosophy.
                        http://bscottholmes.com