232 PETROLOGY OF ROCK COLLECTIONS 



bearing quartz veins and irregular patches a few feet in diameter of coarse biotite- 

 bronzite rock. 



Several fragments of the marble formation appear amongst the rocks collected from 

 the stranded moraines (Fig. 3, Plate IV). These are coarse-grained and granular ; 

 average grain size in the slide 0-8 mm. The rock consists almost wholly of calcite except 

 in dark bands, where graphite makes its appearance. Besides graphite there are minute 

 quantities of quartz, apatite, iron pyrites, and copper pyrites. 



The red-brown biotite met with in the marble series is also a notable constituent 

 of several schists and gneisses from the Dry Valley Moraines. These have the appear- 

 ance of originating from calcareous slates and sandstones. The red-brown mica of one 

 of these specimens, apparently an altered sandstone, was found to contain a notable 

 percentage of manganese, to which, apparently, is due its colour. In another of these 

 rocks is a band rich in poikiloblastic garnets. 



Other fine-grained mica schists originating from sediments are numerous. These 

 are similar to those frequently met with in the metamorphic zone bordering upon 

 granitic intrusive masses. In one case, from Dry Valley, the specimen shows an actual 

 contact of granite and mica schist, the latter representing an original sandstone. 



In this case the granite is an even-grained grey variety. The schist is chiefly com- 

 posed of quartz showing undulose extinction. Strongly pleochroic yellow biotite is 

 abundant. There is present a very small amount of orthoclase showing Carlsbad 

 twins. Minute colourless garnets are frequent. 



One of the specimens from the Stranded Moraines, McMurdo Sound, is apparently 

 an altered greywacke. It is of a general dark grey colour and composed of very regular 

 laminae about 1-5 mm. apart. It consists of mineral grains, chiefly quartz and felspar 

 in the lighter bands and admixtures of ferromagnesian minerals elsewhere. Small 

 particles of pyrites are distributed through the section. 



From the Beardmore Glacier come several specimens of highly crushed granitic 

 rocks which, as already mentioned, there is reason to believe may be metamorphosed 

 arkoses. One of these from the Cloudmaker is of a light yellowish -grey colour showing 

 quartz, kaolinised felspar, and glistening scales of muscovite. Cataclastic structure is 

 evidenced under the microscope, and colourless garnets are frequent. 



A very close-grained dark grey rock from the Upper Glacial Depot is very similar 

 to this in section. In this case granulation is complete. The quartz grains appear 

 as a mosaic under crossed nicols. The base is chiefly composed of alteration products 

 of the felspar, namely, epidote and sericite. Occasional grains of felspar still show albite 

 lamella? with extinction angles corresponding to acid oligoclase. Accessory minerals 

 are ilmenite, magnetite, apatite, and less frequent particles of sphene. 



From the vicinity of the Cloudmaker comes a fine even-grained grey mica schist. 

 The chief constituents are quartz and biotite. It is intersected by irregular veins of 

 quartz and felspar. 



In connection with the Beacon Sandstone reference has already been made to 

 quartzites developed therefrom by the intrusions of dolerite. 



