The southwestern part of Lammetun consists of strongly foliated mylonitic gneisses, which form an important part of the extensive mylonite formations in the Nordfjord–Sogn detachment zone. The area lies in the hinge of an unusually large fold structure, a so-called anticline, between Dalsfjorden and Åfjorden. This fold is part of the major east–west trending folds found between Sognefjorden and Nordfjord, which also include the Devonian basins of western Norway.
The beautiful small folds visible in the metamorphosed gneiss along the smooth coastal rocks and on Langøya are related to these larger fold structures.
