182 AUSTBALASIAN ANTARCTIC EXPEDITION. 



The rock is a little more coarsely crystalline than most of the examples from Cape 

 Gray and the Cape Pigeon Rocks and the granoblastic structure is again prominent. 

 The mineral proportions may be indicated by the following : 



Hornblende 57-7 



Felspar and quartz 35-3 



Pyroxene 2-3 



Garnet 1-2 



Iron ore 1*2 



Biotite 0-3 



Apatite 0-3 



Sphene 0-1 



Residue, including scapolite and talc 1-6 



The green hornblende is again the most abundant constituent and it is occasionally 

 fringed with a little blue glaucophane. At other times an irregular brown tinge is 

 noticeable in some crystals. The felspar is just as clear as the quartz from which it is 

 difficult to distinguish in ordinary light, because their refractive indices are nearly 

 the same. The felspar is an andesine, and the quartz may be set as rounded blebs 

 in the hornblende as well as in the felspar, producing a poikiloblastic structure. There 

 is, however, much more felspar than quartz. 



The 2-3 per cent, of pyroxene is localised in one part of the slide, where it is nearly 

 as abundant as the hornblende. The clear portion has a very pale green colour, but 

 some of it is turbid and dense. Hypersthene is present because a large number of grains 

 show straight extinction. Monoclinic pyroxene is also present because an extinction 

 angle of 37 has been measured. The garnet is again invariably set in felspar (Plate 

 VII., fig. 3). Some crystals are very small and fragmentary but yet perfectly clear 

 and unaltered. Bigger individuals, granular in outline, appear in the larger areas of 

 felspar. 



There are areas in this slide which seem to be analogous to the shear planes that 

 are recorded in Nos. 767 and 771 at the Cape Pigeon Rocks. The bulk of these areas 

 are included in the 1-6 per cent, residue in the percentage mineral composition. In 

 this case these areas have no linear trend except that the pyrite in part seems to occupy 

 a definite plane ; but the analogy is found in their mineral content. The areas are 

 noted for an abundance of fuzzy material which has high polarisation colours and which 

 may be finely granular talc. Equally prominent with this talc is a colourless hornblende 

 which may be bordered with blue glaucophane. The colourless hornblende is often 

 feebly pleochroic and sometimes contains patches of normal green hornblende. Some- 

 times the plates and fibres are bent or broken, and if an extinction angle of 30 can be 

 measured it is interpreted as a colourless pyroxene. There are more prominent areas 

 of scapolite associated with these shear areas along the edge of the slide. 



