242 



AUSTRALASIAN ANTARCTIC EXPEDITION. 



The rocks of class (6) resemble the products of the outer zone of contact 

 metamorphic regions. Pyroxenes are absent, and they are represented by actinolite. 

 Epidote is the most abundant coloured silicate. The rocks are characterised by thei r 

 fine grain, and both structurally and texturally they bear witness to a comparatively 

 low grade of metamorphism. This metamorphism has been sufficient however to 

 give rise to metamorphic felspar in association with epidote. Much of the acid 

 plagioclase, however, must be considered as being originally developed in the rocks, for 

 its mineralogical association with calcite or with quartz points to this conclusion. The 

 degree of metamorphism has allowed recrystallisation, probably with increase of grain 

 size. 



In the carbonate-free rock, No. 128. the epidote and tremolite reactions have 

 proceeded to the exhaustion of the carbonate mineral. 



IV. PARAGENESIS. 



In the following table, the occurrence of the various minerals in the suite of 

 rocks is shown in their paragenetic relationships : 



The part played by the lime-alumina silicates is clearly shown in the paragenetic 

 relations of such minerals as plagioclase, scapolite, garnet and epidote. In dolomitic 

 limestones, they enter only after dolomite and the pure magnesian silicates and 

 aluminate (spinel) have disappeared. Microcline appears in a similar fashion. 

 Detrital sericite is first converted into the magnesian-mica, phlogopite, which is 

 characteristically a member of the forsterite marble group of rocks. This mineral 

 reacts later with silica and calcite giving pyroxene and microcline. 



