What is the original source of the quote, "A dirty mind is a continuous feast."

There are several variants of this quip, which is a takeoff on the old
adage "A contented mind is a continual [or 'perpetual'] feast." It
appears that the originator was Logan Pearsall Smith, an American
writer who lived in London. Smith was popular during the late
Victorian era; most of his writings are long forgotten, but a few
epigrams endure. Like Oscar Wilde, Smith was widely quoted; his pithy,
sardonic observations, some made in print and some in person, have
outlived his lengthier essays.

"A filthy mind is a continual feast", the original version of this
expression seems to come from an American living in London called
Logan Peirsal [sic] Smith who wrote, 'An improper mind is a perpetual
feast', but the shortened version has been used by Oscar Wilde, his
son Vivian Holland and also to Edward Heron Allen who was a friend of
Wilde."

Eccentrica
http://voxx.demon.co.uk/eccent/eccdisp.php?filename=00000096.txt

"An improper mind is a perpetual feast"
(Logan Pearsall Smith, 1865-1946, American essayist)
 
Michelle Owoo: Improper
http://www.michelleowoo.co.uk/Improperx.html

"An improper mind is a perpetual feast. 
 Logan Pearsall Smith (10/18/1865 - 03/02/1946); English-US writer"  

Born Today 10-18
http://www.born-today.com/Today/10-18.htm

Here you'll find several pages of Logan Pearsall Smith's witticisms:

ThinkExist: Logan Pearsall Smith
http://en.thinkexist.com/quotes/logan_pearsall_smith/

A similar quote,"A dirty mind is a perpetual feast," is attributed to
the British critic James Agate.

"It was James Agate who reminded us that a dirty mind is a perpetual feast."

Chess historian Ken Whyld is also quoted as having used the phrase:

Ken Whyld was a wonderful person with the mind - and sense of humour -
of a man half his age. I will never forget the phrase 'a dirty mind is
a perpetual feast', which was his response to the odd-shaped whistling
shrimp on the cover of my first book."

Chessbase: 
http://www.chessbase.com/newsdetail.asp?newsid=1070

Google Search Strategy:

Google Web Search: "mind is a * feast"
://www.google.com/search?hl=en&ie=UTF-8&q=+%22mind+is+a+*+feast%22

Google Web Search: logan smith "mind is a * feast"
logan smith "mind is a * feast"

I hope this is helpful. If anything is unclear, or if a link doesn't
work for you, please request clarification; I'll be glad to offer
further assisance before you rate my answer.

Best regards,
pinkfreud

Great Answer, thank you very much