THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 



45 



The group values together, not individually, represent the chemical characteristics 

 of each main group of the classification. For each main group there is a set of mean 

 group values with a definite range of variation. 



The group values for any example are represented graphically by points in Ozann's 

 triangular projection. If the factor 20 is used, each side of the equilateral triangle is 

 divided into 20 and lines parallel to the sides are drawn through each division. Perpen- 

 diculars are drawn from the angular points on to the sides and the projection values 

 a, c, f, are measured from the base along the perpendiculars. The projection values 

 are calculated thus 



20A 20C 20F 



a = 



C + F' 



c = 



F' 



A + C + F 



The result of this is that differing groups of schists occupy more or less distinct areas 

 in the triangle, and the position of a schist on the projection may give a means of indicating 

 the origin, igneous or sedimentary. 



The dassificatory Position of the Cape Denison Amphibolites. 



If the analyses of rocks Nos. 153 and 629 be treated in this manner, we obtain the 

 following results : 



Group Values. 



