64 AUSTRALASIAN ANTARCTIC EXPEDITION. 



Both these analyses are again very different from that of the amphibolite host. 

 The analysis of the chlorite is very close to that of a pure chlorite, as is seen 

 by comparison with the analysis of a prochlorite quoted from Idding's " Rock Minerals." 

 Its group values place it among the chlorite schists, Group V., though the projection 

 values do not separate the rock from the magnetite schists of Group XL 



The very high values of FeO and MgO in the chlorite rock are notable in 

 comparison with the very low values in the epidosite, while the reverse is true with 

 regard to CaO. The total lime and magnesia is practically the same in the epidosite 

 and in the amphibolite, No. 629, and not much different to the magnesia percentage 

 in the chlorite rock. The total alkalies in the epidosite are also approximately the same 

 as in the amphibolite, with a large excess of soda in both cases. The latter point 

 corresponds with the observed fact that the amount of felspar is the same in both rocks, 

 and that the formation of the epidosite occurs with the replacement of hornblende 

 by epidote. There is also a notable increase of titanium in the epidosite, corresponding 

 to the increased percentage of sphene in the epidosite. 



All the group values of the epidosite, except M, agree with those of Group IX., 

 the lime silicate rocks. But though the value of M is below the stated limits for this 

 group, there can be no doubt that this epidosite should be included in the group of 

 epidosites which appear in the epi division 'of Group IX. 



The projection values of these two rocks are plotted in fig. 6, and it is to be noticed 

 that they fall symmetrically on either side of the position of No. 629. 



Hence from the microscopical and chemical study of these rocks we consider that 

 the epidosite has been derived from the amphibolite during the recrystallisation, and not 

 from a pre-existing magma clot. The same is no doubt true of the chlorite rock, and 

 the conclusion is again forced upon us that there has been chemical migration and 

 rearrangement during metamorphism. It is the type of exchange that we intend to 

 refer to as metamorphic differentiation. 



Geological literature provides many examples where epidosites have been observed 

 in association with amphibolites or hornblende schists. In one instance in the Lizard 

 area Flett has supposed them * to be due to chemical segregation during metamorphism, 

 and our conclusion is a similar one. 



If one still urges that the biotite hornblende schlieren may be the result of meta- 

 morphism of a primary igneous xenolith in a dolerite dyke he is now confronted with the 

 difficulty of explaining why the schlieren have the composition of biotite hornblende 

 in one place, of biotite felspar in a second, of chlorite in a third, and of epidosite in a 

 fourth. Finally he must explain why these four types of schlieren appear as primary 

 metamorphic products, and yet are all essentially different from the relics of the 

 primary cognate and accidental xenoliths that have already been described from the 

 same outcrop of No. 629. 



* " Geology of the Lizard and Meneage," Flett & Hill, p. 50. 



