62 AUSTRALASIAN ANTARCTIC EXPEDITION. 



fragment of gneiss may readily have been caught up in the injection of the dyke. But 

 in the case of the biotite hornblende rock we must picture during metamorphism a 

 transference of material which results in the formation of segregations within the dykes. 

 The formation of a segregation is equivalent to a differentiation in situ, which we 

 propose to refer to as " metamorphic differentiation." 



On such a hypothesis we find a ready explanation for the schlieren of chlorite and 

 epidosite. These two schlieren occurred in the same broad outcrop from which No. 629 

 and the meta-xenoliths were collected. In size they are less than 2ft. in their longest 

 direction. It has been observed from Table I., No. 7, that No. 629 is abnormally low 

 in mica, and this fact can be correlated on this hypothesis with the observed segregation 

 of chlorite. Microscopical examination shows that the chlorite rock is composed 

 entirely of chlorite except for a few very minute grains of magnetite and quartz. The 

 chlorite is green in colour, with very low polarisation colour, but it does not show the 

 blue interference colour common with penninite. In contrast to the biotite hornblende 

 schlieren, the chlorite rock has an approximately massive structure like its host. 

 Further, it is to be noted that where the dominant mica is biotite in the No. 630 band, 

 the mica schliere is composed of biotite. In No. 629, where the dominant mica is 

 chlorite, the mica schliere is composed of chlorite, yet the outcrops of Nos. 630 and 

 629 are less than 40yds. apart. 



The schliere of epidosite occurs 2yds. away from the schliere of chlorite. Its shape 

 tended to be rounded and, like the previous schlieren, no boundaries against the 

 amphibolite were observed. The hand specimens of the epidosite are massive, and the 

 mineral composition of a thin section is 



Felspar 28-4 



Epidote 65-1 



Hornblende 2-5 



Sphene 3-8 



Iron ore 0-2 



Biotite, chlorite, and apatite are present. 



The thin section is illustrated on Plate II., fig. 5. The proportion of felspar is very 

 close to the felspar percentage (27-3) of the amphibolite host No. 629, and its character 

 is the same. The hornblende of the amphibolite is almost completely replaced by 

 epidote in this rock. The epidote is well crystallised, has well-developed cleavage, 

 and its characteristic pleochroism. It may contain inclusions of ragged hornblende, 

 and it can also be observed replacing relic hornblende crystals. The transition is almost 

 complete, but examples can be found where irregular remnants of hornblende with 

 optical continuity are scattered through an epidote crystal. If cleavage be observed 

 in one relic fragment, it is also observed in the associated group. The hornblende 

 possesses a stronger bluish-green colour than in the normal amphibolite, and cross 

 sections still exert their form against the epidote. Sphene is very prominent, and large 



