Stringsinger asks "Does anyone know if the legend is really Scottish?"

There are several legends in Ireland about islands which only appear out of the mist every 7 (or other number) years. Some of these islands are now easily apparent, for instance Tory Island since Colm Cille (Dove of the Church, St Columba) threw his staff on to the island (according to legend). I expect Scotland has similar tales.

And Joan F, I love your thread title. I knew immediately what it referred to.