Dalsetter erratic

The Dalsetter erratic is a large rock built into a low stone dyke. It is about a metre across, smooth and rounded and weighs about two tons. It is an igneous granite type rock composed mainly of large white feldspar crystals which are highlighted by over-growths of reddish-brown stained feldspar. Small amounts of magnetite and quartz are also visible. This composition identifies it as tønsbergite, a type of rock known only from Tønsberg in southern Norway and it is believed to have been brought to Shetland by a glacier. As the only known erratic in Shetland of Scandinavian origin it provides evidence that an ice-sheet from Scandinavia reached Shetland at one time. We know that during the last glaciation no ice reached Shetland from Norway so this erratic may be a stranded visitor from an earlier glacial period. We must be cautious when interpreting foreign stones in Shetland because they might have arrived in ship's ballast or come from Viking homesteads. In this case though, the size of the boulder and the distance from the sea make this unlikely and there is anecdotal evidence that the erratic was dug from a roadside pit close to its present location.