Norway is part of Skandinavia, but the geologic term for this area is the Fennoscandian Shield (or Baltic Shield). This includes Norway, Sweden, Finland and the northwestern part of Russia. The rocks of Norway are very old, the oldest rocks are 3.5 billion years old, and they are generally very much altered by various processes. Typical rocks are crystallines and metamorphites.
Norway has three main provinces of generally different geology. There is the south, around Oslo and down into Sweden, which is called Southwestern Gneiss Province. This area consits of 1,700 to 900 Ma old rocks, most of them formed in the Gothian orogeny (1700-1550 Ma). Later (1500-900 Ma) it was intruded by several generations of granitoids, which lead to various interesting hydrothermal mineral deposits. So this area is spotted with various interesting mining regions, for example there are numerous mines in the area southwest of Oslo. This gneiss province is cut in two parts by the Caledonides, and it continues along the western coast. In the south, where Norway is rather broad, the western gneiss is rather wide, but to the north only the islands are still made of gneiss. These western gneisses were again deformed during the Caledonian orogeny (~400 Ma).
Oslo itself is sitting on the Oslo Rift which is built of very young magmatic rocks of the Permian (300-250 Ma). The Oslo Graben is a failed rift system, which continues into the Skagerrak and the North Sea.
The backbone of the whole country is the belt of the Caledonides. The Scandinavian Caledonides, are made up of Neoproterozoic to Silurian metasedimentary and metavolcanic rocks (700-400 Ma). This rocks were originally deposited in the Iapetus Ocean, the predecessor of the present-day Atlantic Ocean.
Norway has very little limestone areas, so there are just a few caves in this country. Most of the Norwegian caves are sea caves. They are rather short and near sea level, but not necessarily at sea level, as the sea level changed more than 100 meters since the ice ages.
The limestones are mostly located in the Caledonides and about 600 Million years old. Most of these limestones have a long history of subduction, which always means high pressure and temperature. So the limestones were alterated and transformed into metamorphic limestone, called marble, of a grey or blueish colour. This limestones are located in the north of Norway, between Trondheim and Tromsø.
The most famous cave area of Norway is Mo I Rana with 120 caves. The longest cave in Norway is 20 km long Tjoarvekrajgge, which is located about 120 km north of Bodo. It is also the longest cave in the Nordic region . The deepest cave is Ragge Javre Raige.