MACROBERTSON LAND AND KEMP LAND 1S1 



the rocks present similarity with the granite-gneisses carrying conspicuous smoky quartz 

 already described from the Cape Bruce area. 1 Hypersthene ranking only as an accessory 

 is recorded from one specimen carrying both biotite and garnet. 



Of other constituents plagioclase felspar is the chief. Always subordinate to micro- 

 perthite its composition ranges from oligoclase-andesine to an andesine with the same 

 range of refringence as quartz. The plagioclase constituent of the microperthite appears 

 in two forms, the one the normal fine interpositions and the other as spindles and drops 

 less regularly arranged and having the composition of an oligoclase-andesine. These 

 features recall the microperthite textures met with so commonly in the mangerite- 

 charnockite series of rocks. Antiperthite on the other hand is rare but a minor develop- 

 ment of myrmekite textures is seldom absent. Garnet is typically xenomorphic with 

 sieve texture, the enclosures being commonly quartz or biotite. In one specimen the 

 enclosures include a green spinel, the significance of which has been commented upon 

 in discussing the rocks from Cape Bruce. 2 



Two of the rocks falling within the group now described and distinguished by a finer 

 grain are reported to occur in dyke-like masses cutting coarse grained varieties. Apart 

 from specimens of quartz veins carrying garnet and microperthite, the only other 

 distinctive rock type is represented by a hornblende-norite which, however, is not 

 recorded in place. In addition to the dominant hypersthene, labradorite and greenish 

 brown hornblende, the last of which tends to be moulded on the plagioclase, accessory 

 augite and biotite are present. A sub-parallel orientation of the elongate minerals 

 hypersthene, hornblende and biotite imparts a distinctive texture to the assemblage. 



SHEEHAN NUNATAK AREA (KEMP LAND) 



The rocks collected from this area come from Bertha Island, south-west of Sheehan 

 Nunatak. This island, situated in lat. 67 22' S, long. 59 50' E, is separated from the 

 mainland by a narrow channel of frozen water varying in width from a hundred yards 

 to a quarter of a mile. The collection submitted by Mr Rayner consists of ten specimens 

 which show greater variety of composition than the suite from Scullin Monolith 

 (MacRobertson Land). 



The chief rock type of the island is a garnet-hornblende-microperthite-qaartz gneiss 

 containing accessory clinopyroxene and hypersthene. The specimens are medium- 

 grained foliated types weathering to a light brown colour, the foliated character being 

 brought out by streaks of dark minerals (chiefly hornblende). In slice the constituents 

 are seen to be quartz, microperthite, subordinate plagioclase (andesine) — the grains 

 tending to be elongated in the foliation plane, the chief ferromagnesian minerals being 

 green-brown hornblende and garnet. Of the pyroxenes, a green monoclinic hedenbergite 

 exceeds hypersthene in amount. Undulose extinction in felspars and the occurrence of 

 granulitic zones carrying fine myrmekite at microperthite grain boundaries is charac- 

 teristic. 



1 B.A.N.Z.A.R.E. Reports, 1937, Vol. n, Pt 2, p. 22. 



2 Ibid. p. 23. 



