68 AUSTEALASIAN ANTARCTIC EXPEDITION. 



No. 13. Specimen No. 13 is a transition type, and was collected from a similar 

 outcrop to No. 9, but a linear trend was more noticeable. Its boundary with the gneiss 

 is indefinite. It is a rock with much the same granularity as the typical granodiorite 

 gneiss, and this is larger that that of the average amphibolite. Its colour is intermediate 

 between the black amphibolite and the grey gneiss. A coarse crystallisation 

 schistosity is rendered prominent by dark bands of hornblende and white bands of 

 felspar and quartz. This schistosity, of course, reduces the accuracy of the statement 

 of the mineral composition in Table II. 



In thin section we find the schistose bands consist of quartz, of hornblende with 

 biotite and epidote, and of saussuritic aggregates. The hornblende is identical in type 

 to that of No. 9. Chloritisation of the hornblende is not uncommon. Biotite is 

 associated with the hornblende bands, and is found with both a green and a brown color, 

 interlaminated together as before. The brown is more abundant than the green, 

 which is again an intermediate stage between green chlorite and brown biotite. Epidote 

 is very frequently associated with biotite, and is illustrative of a previous conclusion that 

 biotite and epidote are equivalent zonal products of hornblende, and that the biotite 

 appears when there is a supply of potash. The epidote expressed in the quantitative 

 statement in Table II. is that amount of epidote which occurs in this association. A 

 larger amount of epidote appears among the cloudy saussurite, and has been included 

 therein in the measurement. 



The felspar percentage expresses the amount of saussuritic aggregates which 

 include all the cloudy material under the low power objective. Some of the cloudy 

 parts remain dense and unresolvable. Part, however, can be resolved into epidote 

 and a colourless well-formed mica, which is possibly paragonite. Most of this epidote 

 is in fine granular aggregates. Clinozoisite or zoisite is also present. The colourless 

 mica shows strong absorption, and is similar in appearance to muscovite. Rough 

 measurement has indicated that it forms at least one-ninth (|) of the saussuritic aggre- 

 gates, and since the primary felspar is here as in previous cases a calcic plagioclase, 

 we cannot refer it to a potash mica without providing a source for the potash and a 

 means of escape for the soda. The aggregates consist chiefly of epidote and colourless 

 mica, with some chlorite and biotite. No secondary clear albite has been determined 

 with certainty, and quartz grains appear among the cloudy masses, and hence the 

 colourless mica may have absorbed the soda from the felspar. The percentage of 

 biotite is considerable, and this means an absorption of considerable potash. It is 

 reasonable, therefore, to strongly suspect the presence of paragonite mica. 



Quartz is abundant, and provides the chief distinguishing feature from the typical 

 amphibolites. Entering as it does into the crystallisation schistosity it cannot be 

 looked upon as a quartz-veining subsequent to those processes which impressed the rock 

 with the individuality of the schist. It is as essentially part of the schist as the 

 hornblende layers or the saussurite layers. It is clear, and the larger grains invariably 



