AbstractsEarth & Environmental Science

The Oka anorthosite, lying thirty miles northwest of Montreal, was mapped with particular attention to the distribution of the anorthosite varieties present and the geological structure of these occurrences. It was found that the anorthosite varieties were irregularly distributed within the area, even within an individual outcrop. All the anorthosite was classified according to Buddington’s classification of anorthosites. Samples were collected upon which detailed petrographic studies were made. These studies included flat stage and universal stage work on the plagioclase, determination of the anorthite content of the plagioclase by means of immersion oils, and identification of the accessory minerals. Modal analyses were made on a number of thin sections to insure accuracy of naming.