298 



AUSTRALASIAN ANTARCTIC EXPEDITION. 



in the rock. The values for the other rocks are obtained directly irom the chemical 

 analyses in Table V. The projection values are plotted in the triangular diagram, fig. 1. 



An examination of the group values of the garnet-magnetite rocks in Table VII 

 shows that these rocks do not fit in any of Grubenmann's groups of crystalline schists. 

 Column 5 gives the mean group values of Group XI, the iron oxide rocks and these 

 show outstanding differences, especially in regard to S and F, with the corresponding 

 values of the garnet-magnetite rocks. Wide as are the variation limits assigned to some 

 groups of the crystalline schists, it appears impossible to include these garnet-magnetite 

 rocks without the creation of a new group. It may, therefore, be advisable to add a 

 new group of garnet magnetite rocks, just as two new groups have been created (1) for 

 certain manganiferous rocks in India. Hezner has added a manganese silicate group 

 which is naturally united to the lime silicate rocks by all its chemical, mineralogies 1, and 

 genetic relations, and also a new manganese oxide group which best follows the Xlth 

 Group of iron oxide rocks. 



Croup XI 



en Hill 



Nos. 149, 181, and 348 would be types of a new garnet magnetite rock group, 

 while No. 182 would be somewhat abnormal. The chief minerals of such a group are 

 Sarnet, magnetite, and quartz. Other minerals which may be present are biotite, felspar, 

 cordierite, sillimanite, and epidote. Ilmenite, rutile, and hematite may be intergrown 

 with magnetite. Kata zone types are represented by Nos. 149, 827, and 304. Meso 

 zone types include Nos. 149, 814, and 245, while Nos. 181, 288, and 348 have apparently 

 been subjected to epi zone metamorphism as well as meso zone metamorphism. 



On the other hand, if, as will appear likely, igneous emanations are concerned in 

 the formation of these magnetite garnet gneisses, it becomes doubtful whether any 

 attempt should be made to fit them into Grubenmann's classification of the crystalline 

 schists. 



* " Uber manganrejche Kristalline schiefer Indiens." L. Hezner, Neues Jahrbuch fur Mjnerologie, Ac., 1919, p. 28, 



