230 PETROLOGY OF ROCK COLLECTIONS 



RECENT VOLCANIC SERIES 



Rocks of this class are all erratics and were collected from moraines at or near the 

 present sea-level. They have obviously been transported by floating ice from the 

 volcanoes of McMurdo Sound. 



As all the types have been met with in situ, and described either by Dr. Prior or 

 Dr. Jensen, a descriptive list is all that is required here. 



Cape Roberts : Kenyte : Olivine basalt. 



Dunlop Island : Kenyte : Basalts : Phonolite. 



Cape Bernacchi : Kenyte : Olivine basalt. 



Dry Valley* Kenyte tuffs : Scoriaceous and tuffaceous lavas of the kenyte family : 

 Vesicular basalt : Tinguaite. 



Stranded Moraines, McMurdo Sound : Kenyte with glassy base : Kenyte pitchstone : 

 Olivine-bearing kenyte : Glassy basalt with phenocrysts of olivine and augite : Vesi- 

 cular basalt : Vesicular basalt with porphyritic augites : Basalt containing much 

 hypersthene : Vesicular basalt containing porphyritic augite and olivine ; the vesicules 

 are largely filled with radial-fibrous calcite : Fine-grained tuff. 



THE METAMORPHIC HOCKS 



Metamorphic processes are evidenced on a grand scale in the basement complex of 

 South Victoria Land : amongst the types represented, obvious meta -sediments are 

 prominent ; these are marbles, mica -schists and injection-gneisses. Meta -igneous 

 rocks are represented by gneisses and amphibolites. In the case of the newer forma- 

 tions, local metamorphism near contacts is all that is evidenced. The vastness of the 

 subject does not allow of any adequate discussion based on the meagre collection at 

 hand ; but short reference to more interesting rocks only is warranted. 



METAMORPHISM OF THE GRANITES 



The majority of the gneiss exposures have all the appearance of having originated 

 by the dynamo-metamorphism of granite. Many of the granites have been noted to 

 show cataclastic structure and some of the outcrops may be seen passing into gneissic 

 varieties. Coarse granite -gneiss of this kind forms the promontory of Cape Roberts 

 whilst the granite mass of Granite Harbour, close by, shows clearly the first stages of 

 dynamometamorphism : this gneiss contains frequent basic schliers and both these 

 and the gneiss itself closely resemble those of the South Neptune Islands, off the South 

 Australian Coast. 



An erratic block of granite at Cape Irizar, weighing several tons, shows well the 

 early stages of gneissification. This granite is of the Shap Fell type, carrying large 

 rectangular white anorthoclases. Both the mica and the large felspar exhibit a general 

 parallelism. The quartzes have been reduced to a mosaic : the felspars usually show 

 crush only round the edges. It contains, besides the usual constituents, a little grey 

 sphene, pleochroic yellow-brown allanite, and small apatite prisms. 



A Gneissic Granite from a rocky point about eight miles South of Cape Irizar repre- 

 sents a more advanced stage. It is crossed by a narrow epidote vein. The quartzes 

 and felspars are completely crushed to form nests of granules strung out in a linear 

 direction. Accessory minerals are abundant, amongst them are several grains of 

 faintly coloured fluor spar. 



* T. G. Taylor, of the recent Scott Expedition, discovered a local volcanic centre at Dry Valley 

 from which some of these may have originated. 



