This sounds like a magical place for a circle (if that's what it is). Jutting out into Loch Tamanavay (Tamnabhaigh) is a little peninsular, which becomes an island 100ft in diameter during the high spring tides. It has 'a wave washed shore of stones and boulders' (according to Canmore's romantic description). A small 10m diameter grassy mound has many small stones and also 10 larger stones (up to 1m across) protruding from it, including one that Canmore concedes may be a fallen monolith. A 1970s investigation discovered lots of ash just below the mound's surface - so perhaps we can imagine people sitting there on their island with a roaring fire. Sounds great.