92 AUSTRALASIAN ANTARCTIC EXPEDITION. 



constituents form less than 4 per cent, of the slide, whereas the normal ferromagnesian 

 percentage of the granodiorite gneiss is about 18 per cent. Its silicity would, therefore, 

 be probably more comparable with the aplite gneiss than with the granodiorite gneiss. 

 Diablastic interlacings are abundant. Chlorite and epidote are associated with biotite 

 and muscovite. No hornblende is present. Apatite, monazite, and allanite are acces- 

 sories, and of these allanite is the best developed. 



Specimen No. 154 is a similar example, but possesses coarser grain size. There is 

 also a larger ferromagnesian percentage than in the previous case, and the biotite appears 

 in clusters. The irregular distribution of biotite is noticeable in the hand specimen. 

 Muscovite is again present. Large crystals of quartz, orthoclase, and plagioclase are 

 the dominating minerals. Some microcline is present, and the orthoclase does not show 

 much sericitisation. The plagioclase seems to be albite oligoclase or an albite, and 

 is, therefore, the plagioclase of an aplitic vein rather than the plagioclase of the grano- 

 diorite gneiss. Apatite is the most abnormal constituent and forms large crystals 

 which, though not uniformly distributed, contribute 3j per cent, of the slide. Monazite 

 is also an abundant accessory, so that the P 2 5 content of this sample must be unusually 

 high. Allanite is very well developed and zircon also seems to be present. 



The resemblances to the aplitic gneisses are apparent. This likeness can only be 

 reconciled with the field evidence by the recognition of metamorphic diffusion and 

 its obliteration of the individuality of the vein. 



