THE METAMORPH1C ROCKS OF ADELIE LAND. 8TILLWELL. 179 



The rock may be called a hornblende plagioclase pyroxene gneiss. It is similar 

 to the plagioclase pyroxene gneisses of Cape Gray, and in its garnet content it shows 

 affinities with the garnet plagioclase pyroxene gneiss (No. 935) and with the garnet 

 amphibolite (No. 953). 



No. 782. Specimen No. 782 was collected from one of the narrower dykes at the 

 Cape Pigeon Rocks. It is a dark, fine-grained rock with abundant glistening hornblende. 



In section, the rock is found to be quite different in general appearance from No. 

 767, a fact which is eloquently expressed by the following mineral composition : 



Hornblende 49-0 



Felspar 31-8 



Pyroxene 7-6 



Iron ore 7-5 



Biotite 3-7 



Apatite 0-4 



The increased amount of hornblende and the decreased amount of pyroxene is the 

 most important difference ; and it is now noticed that the mineral composition approxi- 

 mates to that of the Cape Denison amphibolites. If all the pyroxene had disappeared 

 the proportion of hornblende to felspar would be the same as in some members of that 

 series. 



The green hornblende is thus the most abundant mineral in this slide. The horn- 

 blende crystals, together with the more rare crystals of brown biotite, show a more 

 or less parallel arrangement, indicating the schistose nature of the rock. Very rarely 

 a colourless hornblende is intergrown with the green hornblende, similar to part of that 

 seen in the shear zone in No. 767. Both hypersthene and augite can be found among 

 the relic pyroxene distributed in patchy areas throughout the slide. It is often in 

 fragmentary form, and the fragments which are set in felspar can be determined by 

 polarised light to have been parts of a large crystal showing poikiloblastic structure. 

 Part of the relic pyroxene is altered to a greenish-brown micaceous product. The 

 felspar is again perfectly clear and ilmenite is abundant as usual. Pyrite is present. 



The presence of the pyroxene makes the relation of this specimen to the hornblende 

 plagioclase pyroxene gneiss No. 767 obvious, and the primary types must have been very 

 similar. The differences are due to varying conditions during metamorphism. The 

 pyroxene felspar areas also suggest a likeness to the type No. 942 from Stillwell Island, 

 in which hornblende is not so abundant but the pyroxene areas more prominent. The 

 rock may be called an augite amphibolite. 



No. 771. A closely related type to No. 782 is No. 771. This specimen has a much 

 finer grain and is less schistose. 



It consists of a fine granoblastic mass of hornblende and felspar, with insignificant 

 amounts of biotite and ilmenite, but the latter may be surrounded by sphene. There 



