164 AUSTRALASIAN ANTARCTIC EXPEDITION. 



THE CRYSTALLOBLASTIC ORDER. 



It is found difficult in some cases to satisfactorily name the crystalloblastic order. 

 This order contains a list of minerals which have arisen more or less simultaneously 

 during its recrystallisation. If all the minerals in the rock have not formed at the 

 same period, then they cannot be placed in a single crystalloblastic order, and it 

 frequently happens that a rock carries traces of two metamorphic phases each 

 characterised by certain minerals. Sometimes two minerals in a rock may not come 

 in contact, and their relative position in the order cannot be fixed. In some cases, as 

 at Madigan Nunatak, the contacts may be wholly or partially replaced by areas of 

 pulverised material. 



In the garnet cordierite gneiss, garnet and sillimanite crystals have not been observed 

 in contact, and are bracketed in the crystalloblastic, which appears to be as follows : 

 Garnet, sillimanite, ilmenite, biotite, felspar, cordierite, quartz. 



In the cyanite felspar gneiss from Garnet Point the cyanite exerts its form against 

 the biotite and must, therefore, be placed above the biotite in the sequence. In this 

 case the cyanite cannot be compared with the garnet or cordierite, as these are looked 

 upon as secondary relics from the kata zone metamorphism. 



In the hypersthene alkali felspar gneiss, No. 949 (charnockite), the observed order 

 is Apatite, ilmenite ; hypersthene ; biotite ; felspar ; quartz. 



In the less acid, hypersthene felspar gneisses, containing garnet, the garnet is sub- 

 sequent to the formation of most of the biotite, and is, therefore, omitted from the 

 sequence, which appears to be Apatite, ilmenite ; pyroxene ; biotite ; felspar ; quartz. 



SUMMARY. 



Garnet gneisses are obtained from Cape Gray, Garnet Point, and the Cape Pigeon 

 Rocks three rocky outcrops on the present shore line that are accessible to a sledging 

 party on the mainland. A fourth locality is Stillwell Island, distant nearly two miles 

 from the shore line, and was visited by the ship's boat. 



The gneisses may be summarised thus 



Cape Gray Garnet cordierite gneiss. 



Garnet Point Cyanite biotite gneiss. 



Garnet felspar gneiss. 

 Stillwell Island Garnet felspar gneiss. 



Hypersthene felspar gneisses. 

 Cape Pigeon Rocks Garnet gneiss. 



Hypersthene biotite felspar gneiss. 



The garnet felspar gneisses on Garnet Point and Stillwell Island are light coloured 

 and mottled by large aggregates of garnet and biotite, which are more or less spherical 

 in shape and up to 2in. in diameter. These aggregates represent original and complete 



