Sigh, with just a bit of research in Alan Gribben's astounding reference 
volume I found Richard E. Burton, son of Nathaniel Judson Burton.  And, 
following that is an entry for Richard Francis Burton: "Personal 
Narrative of a Pilgrimage to El-Medinah and Mecca" reportedly signed by 
Clemens.  I still wonder why Sam was apparently unaware of Burton's 
"City of the Saints" first published in the US by Harper and Brothers in 
1862.

On 10/9/23 15:14, Scott Holmes wrote:
> There is an entry in Day By Day for May 17, 1788 that has me 
> puzzled:*May 17 Thursday* – *Frederick J. Hall** for Webster & 
> Co.* wrote to Sam: “Your favor received, also the watch. We will pay 
> the Burton bill, the bill for composition and electrotyping on the 
> Burton book, and also send you invoice for the watch. We have 
> forwarded a copy of ‘The Library of Humor’.” Other finances were 
> discussed [MTP]. /Note/: *Richard E. Burton*.
>
> Who is this Burton and what book did he write?  This cannot be Richard 
> F. Burton, who figures so much in my treatment of Sam Clemens' travels 
> to Carson City.
-- 
/Unaffiliated Geographer and Twain aficionado/