Hurricane Matthew Washes Up Civil War Cannonballs in S.C.-- Part 5: What Type of Projectile and How'd They Get There?

Members of the United states Air Force Explosive Ordnance Team, Folly Beach Fire Department, Emergency Medical Services and Charleston County's Sheriff's Office responded to the call.

The Daily Mail of the United Kingdom said that Folly Beach is about eight miles south of Fort Sumter.

I have to wonder if they washed up on shore or were uncovered?  What kind of cannonballs were they (what type of cannon would have fire them)?    Were they intentionally left during the Civil War?  What was the name of the fort or fortification (likely a supply depot because of its distance from Morris Island and Charleston Harbor.)?

--Old Secesh