Flame photometric analyses for K₂O and Na₂O were run on 31 samples of the Precambrian igneous rocks of Missouri. Samples were collected from the field, physically prepared and dissolved by a standard method and a modified standard method of rapid silicate analyses. The K₂O, Na₂O values obtained are averages between two methods of analyses. The modified method reduces by 80% the time required to chemically digest a rock sample. The results for both methods are not significantly different. Curtin and Company Advanced Flame Photometer was used.
Results have been plotted on graphs and a chronological sequence for the named Precambrian igneous rock units of Missouri is indicated. It is suggested that the Middlebrook Group belongs to a separate magmatic cycle; that the Van East, Musco, and Bevos Groups belong to the same magmatic cycle; and that the basic intrusive rocks belong to a separate magmatic cycle --Abstract, page ii
