Lågendalen valley in Lardal is a clear U-shaped valley, with the river Lågen meandering in the bottom. It is not without good reason that Lågendalen is often advertised as the “green valley”. The soil is very fertile, thanks to geological processes.
Toward the end of the last Ice Age, Lågendalen valley was an arctic fjord that stretched all the way up to Kongsberg. The clear division between agricultural and forestry areas in Lågendalen lies at about 170 meters and is a measure of how high the sealevel reached when Lågendalen was an arctic fjord. This is called the marine limit. Under the marine limit, the agricultural areas lie on marine clay that was deposited on the bottom of the Arctic fjord. Such marine clays make wonderful growing soil. They are rich in nutrients, they hold in moisture and they are relatively easy to plow.
Rombeporphyry is a typical rock type in Lardal. It flowed out as lava about 300 million years ago. Lardal has only a few of the many types of rombeporphyry in the Oslo Rift valley. We see most of the Gjetranger type such as may be found for example in the Kjærra Fossepark. Perhaps the most beautiful rombeporphyry of all is the Moen type. It has crystallized with a star-like structure and occurs only at Moen by Steinshold.