Beskrivelse til kartbladet Dønna

Abstract

Forkortet: This region is situated in the Northern part of the district of Helgeland between 66\u00B0 and 66\u00B0 20' N. A geological map in black is given on pages 4 and 5. The igneous rocks here are granites, gabbro and peridotite. The granites for the most part show a schistose arrangement of the mineral constituents. They are supposed to have been altered by regional metamorphism. Frequently the granites have porphyritic structure with great crystals of redish to grayish white orthoclase. Two types of granite occur here. The one contains hornblende in so great a quantity, that is ought properly to be termed a hornblende- granite. It also contains biotite and as a exception, also muscovite. Small crystals of brown titanite are not seldom to be seen in it. The glacial stri- ation indicates that the ice on the high ground has moved in directions almost at right angles to the coastline or between WNW and NW. At the close of the Ice Age the land in this region was submerged to a height of from 92 to 116 m above the present shore-line, less at the coast, more in the interior of the land. To this epoch belong many raised beaches or elevated shore-lines which have been eroded in the solid rocks. Upon the same level as the elevated shore-lines many caves occur which have been eroded by the sea on fissures in the rock.