THE METAMORPHIC ROCKS OF ADEL1E LAND -ST 1 1. 1. \\KLL. 77 



schistosity, favour an origin by metamorphic differentiation. The neighbouring areas 

 to the hornblende differentiates are frequently enriched in felspar when the rock assumes 

 a lighter colour. That this hornblende differentiation only appears in the less distinctive 

 amphibolite patches simply means that the conditions for the hornblende differentiation 

 have been accompanied by conditions permitting metamorphic migration on a greater 

 scale than in the biotite differentiation. 



Differentiation seems to have occurred in two other basic clots. In one, No. 928, 

 there are exceptionally large percentages of sphene and magnetite. In the section 

 the measured percentage of sphene is 13'1 per cent. The iron is segregated in coarse 

 crystals and, as only one or two crystals appear in a section, it is impossible to get an 

 adequate idea of the proportion of magnetite in the rock from a single section. The 

 magnetite crystals are as much as Jem. broad and are abundant in hand specimen. 

 In thin section they always possess the normal sphene rim, and in the large crystals 

 the sphene rim is very thin. The abundant sphene crystals are large and are mostly 

 without a magnetite nucleus. Some are twinned and some enclose biotite, but are more 

 often surrounded by biotite. Biotite, felspar, quartz are also present in the rock. The 

 biotite is the most abundant mineral and absorbs the ferromagnesian content. No 

 hornblende is present, but there is a small amount of colourless muscovite. The felspar 

 is fairly evenly distributed through the slide, but clusters of felspar crystals are 

 noticeable in the hand specimen. The felspar is perfectly clear and colourless, but 

 some quartz can be recognised. Small apatite crystals are abundant and there are 

 odd grains of pyrite and epidote. 



No. 928 was collected from the eastern side of Cape Denison, but coarse sphene 

 rocks were also noticed close by the magnetograph house, the locality of No. 9. The 

 extraordinary sphene content cannot be due to mere chance. The clot must be 

 considered as part of the dyke series, and it would be very difficult to account for the 

 high titanium percentage without an appeal to a metamorphic agency. The sphene 

 and the magnetite are metamorphic minerals, and we can look upon this rock as an 

 example of metamorphic differentiation wherein both the sphene and the magnetite 

 contents have been enriched. The abnormal amounts of sphene and magnetite are 

 reflected in the high specific gravity (3-10). 



Specimen No. 143 is another example of a basic clot in which metamorphic 

 differentiation has occurred. The specimen is rich in magnetite, and the magnetite 

 crystals stand out prominently on the weathered surface. They are not quite so large 

 as in the preceding case and can be seen to be distinctly oval in section. The longest 

 diameter may be 4mm. and the shortest as much as 2mm. Some seem to have crystal 

 boundaries and others are more rounded. Surrounding each magnetic bleb is a zone 

 of white felspar, which can be plainly seen in the hand specimen and is noticeable in 

 the photograph (Plate IX., fig. 6). Separations of magnetite were made in both this 

 case and the preceding specimen (No. 928). In both cases tests were made to detect 



