A very good discussion can be found in Kent Rasmussen's MARK TWAIN A TO Z.

                                Everett Emerson
                             130 Lake Ellen Drive
                        Chapel Hill, NC 27514-1937
                                (919) 967-2652

On Tue, 15 Apr 1997, Sylvia Wendel wrote:

> Dear friends,
> I would like to know if there are books or articles dealing specifically
with
> the relationship of Samuel and Orion Clemens.  In a cursory way, I know
Orion
> was a "dreamer" who was largely supported by Sam in various crackpot
schemes.
>  I know Orion had a wife and kids.  i have (in my "Portable MT") at least
> some correspondence from S. to O.  Does a collection of all their letters
> exist?  Didn't Sam at one point become disgusted with Orion and refuse to
> provide him with any more $$?
>
> Any info regarding these two will be welcomed.  Thanks.
>
> Sylvia Weiser Wendel
>