88 



AUSTRALASIAN ANTARCTIC EXPEDITION. 



3. Partial saussuritisation of plagioclase. 



4. Partial change of orthoclase into sericite. 



5. Development of microcline from orthoclase. 



6. Development of perthite from plagioclase. 



7. Development of secondary biotite from chlorite. 



A7 V W W VV\ A / 



AAAAA A/ VVWVXAAA A 



\AA7V 



Fig. 9. 



I. Mean position of Group I., the Alkali Felspar Gneisses. 

 III. Mean position of Group III., the Plagioclase Gneisses. 



A. Rainy Lake Gneiss. 



B. Scottish banded Gneiss. 



C. Granodiorite Gneiss, Cape Denison. 



The general survey of these changes indicates that the conditions of Grubenmann's 

 epi zone of rock metamorphism have been dominant. The last three changes indicate 

 that there is an approximation to the meso zone conditions, and so also does the 

 occasional development of a rough crystallisation schistosity. Hence, while we consider 

 that the rock may be referred to as an epi granodiorite gneiss, the meso zone tendency 

 should be recognised. 



