44 AUSTEALAS1AN ANTARCTIC EXPEDITION. 



is to succeed in grouping together similar species. The following are the groups appearing 

 in his classification : 



1. Alkali felspar gneisses. 7. Chloromelanite rocks. 



2. Aluminium silicate gneisses. 8. Quartzite rocks. 



3. Lime soda felspar gneisses. 9. Lime silicate rocks. 



4. Eclogite and amphibolites. 10. Marmorites. 



5. Magnesium silicate schists. 11. Iron oxide rocks. 



6. Jadeite rocks. 12. Aluminium oxide rocks. 



Each group has its kata, meso, or epi division based on the characteristics of the 

 lowest zone, the middle zone, and the highest zone of metamorphism. Each division 

 again consists of families whose number depends on the number of known types of 

 schists contained in the division. 



The classification is made quantitative by the use of an adaptation of Ozann's 

 treatment of a chemical analysis. The analysis is first modified so that the Ti0 2 and 

 P 2 5 are reduced to equivalent amounts of Si0 2 percentage ; the Fe 2 3 , MnO, Cr 2 O 3 , 

 NiO, CoO, are reduced to, and then added to the FeO percentage, the BaO, SrO, to the 

 CaO, and the water neglected. The values of the seven constituents are then reduced 

 to their molecular proportions, which, in turn, are reduced to molecular percentages.* 

 From the molecular percentages seven group values, designated S, A, C, F, M, T, K, are 

 obtained in the following manner : 



S denotes the Si0 2 in molecular proportion. 



A is the similar sum of K 2 and Na 2 which is combined with A1 2 3 in the 



1 : 1 proportion. 



C is the CaO combined with A1 2 3 in the 1 : 1 proportion. 

 F is the sum of FeO and MgO and that part of CaO which is not absorbed 



in the 1 : 1 proportion with A1 2 3 . 

 M is the residual CaO used in F. 

 T is the residual A1 2 3 not absorbed in the 1 : 1 proportion with K 2 0, Na 2 0, 



and CaO. 



a 



K is the value of the quotient . =F, 



6A + 2C + F 



The values S, K, A, C, F are used exactly with Ozann's meaning ; K, however, 

 is only important here in determining the degree of acidity of the crystalline schist. 

 M gives the absolute amount of CaO in F and is useful in dealing with lime silicate rocks 

 signifying their sedimentary origin. T is necessary to express the high A1 2 3 content 

 in some gneisses, especially those derived from clay sediments. No term is introduced 

 to express the relation of the alkalies to one another as it is undesirable in the present 

 state of our knowledge of the crystalline schists. A classification at present can only 

 deal with the broader features. 



* The extra step, explained by Grubenmann, op. cit., vol. II., p. 12, of reducing the seven values to percentage values 

 before determining the molecular proportions, is superfluous. 



