From what I remember, there was a jumble of rocks that may possibly, once have been a circle... not as well defined as the Grubstones. I don't remember a noticeable standing stone, but that doesn't mean there wasn't one. Some low boulders looked like they may have been placed and there may have been more under the heather. Hard to remember now - must be well over a decade since I last visited the spot.
No, I haven't been onto Rivock Edge. Went into the woods once with the intention of finding carvings, but the mozzies drove me away before I found anything. Didn't make it back that way on last few visits. I hear Rivock Edge - or at least the plantation - is up for sale? Area is said to be haunted by a figure in a grey cloak... reckon it's just some geezer trying to keep the mozzies off meself! :)
Andy (Kozmik Ken is my posh nom de plume!)
