14 AUSTKALASIAN ANTAKCTIC EXPEDITION. 



Apart from the metamorphosed dyke series the Cape Gray Promontory is noted 

 for its highly garnetiferous gneisses. The garnets are most remarkable at Garnet Point 

 and at Still well Island, where they are found l^in. to 2in. in diameter, and give the 

 outcrops a curious mottled appearance. These large garnets are always partly altered 

 to biotite and quartz, which appear in cracks and around the edges of the crystals. 

 Cordierite, sillimanite, and corundum are found in different specimens and indicate the 

 high alumina content. Very beautiful pleochroic haloes are found in some of the biotites 

 of these gneisses. Some show an inner nucleus and an outer corona, while some change 

 the colour of the biotite in their sphere of action from a pale green to a brown. 



At Garnet Point and the Cape Pigeon Rocks dykes containing prominent garnet 

 and felspar cut the garnet gneisses. A single specimen from one of these has indicated 

 its relation to the hypersthenic felspar gneisses on Stillwell Island. Very extraordinary 

 variation has been discovered in the mineral content of these hypersthene garnet rocks, 

 which correspond to the intermediate members of the charnockite series. At one end 

 of a specimen Sin. long, garnet is present, and has been produced by the reaction between 

 biotite and plagioclase and quartz, while, in a section cut from the opposite end of the 

 specimen, garnet and all evidence of reaction are absent. In other cases biotite and 

 quartz result from reaction between hypersthene and orthoclase, while in one case 

 the garnet seems to be formed directly from the hypersthene. Garnet-forming 

 conditions may therefore be highly localised, and all the evidence that has been collected 

 is antagonistic to Fermor's conception of an infra-plutonic zone a deep zone in the 

 earth's crust which is supposed to be characterised by garnets. The evidence reminds 

 us that the metamorphic zones are not denned by certain depths in the earth's crust, 

 but by a set of physico-chemical conditions. 



The study of the examples in Adelie Land of destroyed igneous boundaries, of the 

 metamorphic differentiation products, of the mineral changes, and of the development 

 of large crystals during recrystallisation leads us to believe that solid diffusion in rocks 

 is an important factor that needs to be considered in the detailed study of the develop- 

 ment of the crystalline schists. 



