1500 million of years of geological history.
Skien is a community with an exceptional geological diversity. A tour across the Skien-Gjerpendalen valley is a tour through 1500 million years of geological history.
To the west and northwest of the city Centre lies ancient basement rock. These rocks are old, more than 1000 million years, with traces of mountain building that took place perhaps more than 1500 million years ago. In the Gjerpensdalen valley one sees a combination of limestone’s overlain by marine clay.
The limestone ridges trend in a north-south direction, and they represent a seafloor formed in an ancient tropical sea. About 450 million years ago, the continental plate that Norway lies on was located south of the equator. The continental plate was largely covered by a sea, in which many plants and animals lived. Many of the animals had calcareous shells, and it is the remains of these calcareous shells that form the ridges, layer by layer. On Kapitelberget, the Krypt Church is built in the remains of a coral reef from this time.
The marine clays in Gjerpensdalen valley were formed in an artic fjord some thousands of years ago. When the big ice sheet that covered Scandinavia 12,000 years ago melted, sea water flowed in over our depressed land. The clays help to make the soil fertile. Another contribute to the fertility of the soil the basalts to the south of the valley. The basalts are lavas that flowed out from the volcanoes about 300 million years ago. There is lush leafy vegetation on these volcanoes deposits, that is very visible in the terrain.