To be fair to illustrator True Williams in regard to the style
of fence he drew in _The Adventures of Tom Sawyer_ and other
scholars who have untangled the fence discrepancy, see Beverly
David's discussion of the fence illustration in her book
_Mark Twain's Illustrators, Vol. I_, p. 246-247.

Williams drew illustrations from Twain's original manuscript which
stated the fence measured only four feet high.  The dimension was later
changed with strike marks on the original manuscript.  Williams
himself later drew and published a Tom Sawyer illustration of a
fence using vertical planks.  I have both True Williams illustrations
of the fence online side-by-side in this feature:

http://www.twainquotes.com/TWW/TWW.html


Barb