The first two are reasonably close to the mark - the most striking feature is that, in the areas where cotton wasn't grown in 1860 (an activity which invariably involved large numbers of slaves), the proportion of the rural population which is African-American is small.
The map overlay I was referring to is at:
http://strangemaps.wordpress.com/2008/11/15/330-fr...
The most striking anomaly is the area in Tennessee with a lot of cotton in 1860 but a low African-American population now. This may have something to do with the county in question being national headquarters of the KKK for a while.
The racial split in voting was remarkably striking in some of the southern states: in Alabama, whites voted 88% Republican and blacks 97% Democrat. It reminded me of a line someone once used about a Bosnian election and the performance of various nationalist parties: 'that wasn't an election, it was a census'.