This is a Trowie (Faerie) tune from the Shetland Island of Fetlar ('the fat isle'). It was heard by a man named Garster, coming from a hole in the ground while he was resting by a Trowie Knoll (Fairy Hill) on his way home from a wedding. He attributed the tune to the trows, the island’s version of Scandinavian trolls, but others scoffed and said he must have fallen asleep and dreamt it (hence the name)