Nordre Femund. Beskrivelse til det geologiske rektangelkart.
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- Artikler 
The rocky ground is both in the valleys and on the greater parts of the mountain wilds covered by glacial drift, and is therefore visible only to a minor extent. On the summits the rock is more uncovered, but here it is usually so broken by frost that it is \"lying in ruins\". Among the occurring formations the Archæan rock is the oldest one. It consists of more or less pressed igneous rocks, specially granite with veins of diabase and gabbro. The Archæan rocks differ greatly in the various districts where it is uncovered, and the younger veins crossing older ones - mostly porphyric granites - seem to be less metamorphosed than the older veins. In Tufsingdalen, near the farm Røsten, occurs a coarse-grained holocrystalline granite, which, when bording to younger formations, is displaying an advanced disintegration. In a layer, almost 20 m thick, under the basal conglomerate of the above lying formation the grains of the granite have been submitted to a selection. The number of the quartz-grains have increased on the expense of grains of feldspar and mica. The remaining feldspar is completely altered into kaolin and it is no longer possible to distinguish microline from plagioclase. In the original granite the microcline is relatively fresh, and - although the plagioclase shows a very advanced metamorphism - traces of albite lamellas can be observed microscopically at the edges.