Based on observations made during an excursion together with Prof. T. Barth in the Opdal-Sunndai district in the north-western part of Southern Norway in 1936, the conclusion has been arrived at that rock masses of the said district, hitherto generally regarded as beionging to the Archæan, must represent younger rocks, Iargeiy Eocambrian feidspathic sandstone (sparagmite) in highiy metamorphic facies. The present contribution gives the results of more comprehensive fieid investigations undertaken in 1937 with the object of settling more de finiteiy the question of the age, and aiso of the structurai conditions, of the rock-compiexes. In a following paper, Prof. Barth deais with the petroiogical and chemical character of rocks from the area.