I'm not far from you, I'm just across the Savannah River in Southeast South Carolina, I have been in this area for 42 years and I have been in the building industry most of that time and I have never seen any old black bricks in this area, any blackish colored bricks I have seen were modern and colored with dyes, of course an occasional re-claimed brick are sometime black but that from being in a fire.
That being said it's possilbe that the brick was made local to the area it was found, I would suggest that you check around with the area's brick suppliers, this area is big on "re-claimed" old bricks and most brick suppliers have a selection of what is from this area, they maybe able to help you on what type the brick is and approximately the age.