part 2] GEANITE-GISEISSES OF SOUTHERN" EYRE PENINSULA. 121 



equilibrium prevailing in the crystallizing magma; as sliOAvn in the 

 equation 



MgFerSiOa), 7^ (Mg-Fe)SiO, 4-SiO.,. 



N. L. Bo wen & 0. Andersen have shown that the resorption o£ 

 olivine-crystals with the development of reaction-rims of enstatite 

 is a factor involved in the normal crystallization of basaltic melts, 

 .as a simple result of cooling.^ The hypersthene border has all the 

 appearance in the granulitic type of having been recr^^'stallized in 

 course of metamorphism. 



Garnet is not so abundant a constituent of this rock as of 

 No. 85, but its relations are again the same. 



In another band from the same region (No. 89) a further 

 change has developed. The constituents are again plagioclase, 

 augite, hypersthene, magnetite, hornblende, and biotite. 



The differences to be noted are the great percentages of horn- 

 blende and a changing texture. The amphibole is now the most 

 important ferromagnesian mineral, and the blastophitic texture is 

 all but lost, a more granoblastic arrangement being now impressed. 

 The garnet-pyroxene complexes are, hoAvever, still preserved, and 

 the granulitic character of the pyroxene remains to indicate the 

 relationship Avith the rocks previously described. 



The actual size of grain of the amphibole tends to be a little 

 greater than in the pyroxene ; but traces of the pyroxene-amphi- 

 bole conversion are still preserved, and the hornblende has been 

 formed in this way. All stages of this transformation can be 

 noted. 



The microscopical features of the garnet-pyroxene complexes are 

 identical with those of Nos. 85 and 221. All the 'relict' augite 

 has disappeared ; but some of the larger hornblende-grains may 

 represent this transformed. 



This rock, therefore, presents the features of the preceding t3qDes 

 on which a hornblendization has been sujDerposed. This horn- 

 blendization can most readily be accounted for b}^ a development 

 in a declining stage of metamorphism : that is, Avhen a decline of 

 metamorphism from its maximum had set in, being an adjustment 

 of equilibrium accompan^dng the cooling of the rock. 



An interesting type from Cape Euler, south of Tumby Bay, 

 presents a further feature of interest. The texture is typically 

 blastophitic, but in addition there are present a number of granu- 

 litic aggregates of quartz and orthoclase, and the rock exhibits 

 many of the characters of the quartz-dolerites. 



' Kelict ' augite is present, recognizable by its inclusions and 

 fibrous diallagic appearance. The secondary granulitic pA^roxenes 

 include both the monoclinic and rhombic varieties, as before. 



^ ' The Binary System MgO-SiO., ' Amer. Journ. Sci. ser. 4, vol. xxxvii 

 (1914) pp. 487-500. 



