Ah, I found it...not an article at all but a book review of _A Companion to
Mark Twain_ in which the sage Mr. Berkove, in the "Mark Twain and Others"
section, says:

"Having learned from the best, Twain eventually bettered his instructors.
Every substantial work of fiction that he wrote for the rest of his life has
hoaxes at its core--some of them extremely subtle and sophisticated and very
serious. This was the principal Nevada legacy to his writing. It was one of
two distinguishing constituents of his style" [164].

David H Fears