Within the Camp, near the brow of the hill are 'Fairy Sleets', these, as the Rev. HH Winwood explained, are 'slits', narrow and shallow trenches formed when ore has been found by cutting through the rock to follow it out.
I found this in the 1904-08 volume of the Somersetshire Arch Soc Proc (Bath Branch). Perhaps someone knows more about to what it refers?
Blacker's Hill is a promontory fort, protected by still impressive earthworks on the north and west, but otherwise defended by steep (and steepened) slopes. There are three entrances, but it's not clear how many of these are original - the fields have been changed about over the years and there's been some quarrying too. Perhaps there was just one to the NE. Springs and a stream run along the south of the fort, and there are various barrows nearby to the north. The site's been excavated and 'geophysed' - you can read about it and the nearby barrows here at the Somerset Historic Environment Record. A 1950s excavation found traces of smelted iron in one of the ditches, and the geophysics detected several enclosures, linear boundaries, roundhouses and pits: different phases of the fort's use. Sounds like a busy community - something to think about if you choose to visit.