Perhaps this might help?
I remembered a tour we took in Charleston about fifteen years ago, and the description of the streets and pathways as "the crunch of tabby" underfoot, here is a source that confirms my 'back-of-my-crowded-mind-memory' about oyster shell streets. I do believe the cobblestones would have been red Charleston brick, for rounded stones would have had to come from a far ways, but they may have used ballast rock from the many ships which docked at the Charleston Harbor.
I have no source, but from the caverns of my mind, or perhaps, John Jakes' "Charleston." Ballast rock would help to balance a ship that was not completely loaded, and then the rocks were removed when sufficient cargo was stowed.
source:
http://www.discovercharleston.com/cuisine/food-flair.htm
"Food Fact: A Historic Pearl
In season, oysters are practically a Charleston staple. In fact, White Point Gardens, also known as the Battery, got its name from the large mounds of white oyster shells that once covered the point of Charleston's peninsula. They were present in such large quantities that crushed oyster shells once made up the streets and sidewalks of Charleston."