I wasn't convinced it was a stone circle either - looked kind of cairn-like to me. As you say, Margaret didn't dispute it was old, just not convinced it was a circle - probably because it isn't similar to any others on the island. Joolio thinks it's a circle if that's worth anything.
Took a tramp around the hill opposite to see if there was anything there, a couple of possibles including a standing stone which may or may not have been part of some other stones.
Anyone notice the strangely flat area on the hills behind? (formed a kind o U on the horizon) I went and had a look and it was flat enough to have been a cultivated area, but there was a fence running down the middle of it. Possible a viewing platform I thought, although the angle wasn't quite right for the part of sleeping Beauty I thought might reveal something.
moey