In this paper, the author summarizes his investigations into the occurence and distribution of dolomite and magnesium-silicate minerals in Svecofennian carbonate rocks. As a result of his investigations, the author has come to the conclusion that it is very probable that dolomite rocks have originated in a prehistoric sea, either by direct chemical precipitation or dolomitization of limestone during an early stage of diagenesis. The theory that dolomitization first occurred during the orogenic period of the Svecofennian evolution, which theory is propounded in current Swedish literature, is considered unlikely. On the other hand the opposite is possible,i.e., that the dolomite rocks were partially de-dolomitized during a period of metamorphism and gave rise to limestone and solutions containing magnesium which could result in magnesia metasomatism of the contiguous rocks.