Thank you Robert, Richard Reineccius, Kevin Mac Donnell, and Stanton Nesbit
for your excellent and helpful responses.  I have never been to the
Mississippi valley  nor have I seen any of the places he wrote about in his
descriptions of learning piloting.  I am also somewhat new to Twain's
writing and life so I am not sure where to go for references "about" his
work (I recently checked out and started reading Horst H. Kruse's 1981 book,
"Mark Twain and 'Life on the Mississippi'").

I have another question related "Life on the Mississippi" that I am posting
to the list, momentarily.