part 2] OF SOUTHERN ETllE PENIIN'STJLA. 131 



granites of the charnockite-tj^pe, and a great development of 

 garnet-gneisses. The pegmatites are predominantly horn- 

 blendic types, with diopside as an occasional constituent. 

 (8) The gneissic structure developed in these rocks is a primary 

 gneissic banding arising from flow-movements in a hetero- 

 geneous magma. The nature of the heterogeneous magma, 

 and the conditions under which a foliation and banding are 

 developed are discussed. 



(4) Included within the granite-gneisses, and alternating with 



them, is a series of amphibolite-bands oriented in parallel. 

 They include amphibolites proper, pyroxene-amphibolites, 

 pyroxene -granulites, and quartz -orthoclase amphibolites. 

 These amphibolites are of anterior origin with respect to the 

 acid gneisses, and I give a description of the evidence on 

 which this conclusion is based. 



(5) In addition, there are fragments of highly metamorphosed 



sediments, identical with members of the earlier Hutchison 

 Series, enclosed within the acid gneisses. These include 

 diopside-rocks, garnet-biotite schists, and xenoliths of garnet- 

 and green spinel-sillimanite type. 



(6) The amphibolites have the mineralogical composition of basic 



igneous rocks. In the case of the quartz-orthoclase bearing 

 types, an analj^sis shows a close resemblance to certain 

 quartz-gabbros. This is further contirmed by the presence 

 of an amphibolite-band, of the composition of a micro- 

 pegmatitic dolerite at its centre, passing into a normal 

 quartz-bearing amphibolite at the periphery. 



The metamorphism and the origin of these rocks are dis- 

 cussed. The}^ represent earlier consolidated rocks which have 

 become involved and engulfed in the later acid gneisses. 



Some posterior dykes of basic charnockitic composition 

 cut the acid gneisses, at various localities. 



(7) Of more than ordinary interest are certain bands of doleritic 



type, which are intercalated in the gneisses of Kirton Point 

 and Boston Island. These appear to have experienced a 

 metamorphism of the highest grade. The pyroxenes have 

 been recrystallized, and garnet abundantl}^ formed. Hyper- 

 sthene and garnet have arisen in part as a i-esult of a degra- 

 dation of a complex pyroxene molecule. The nature of the 

 chemical changes induced by this high-grade metamorphism 

 is discussed. 



It seems probable that t^:(:se dolerites are earlier rocks, 

 engulfed and thermally metamorphosed by the granitic 

 magma. 



(8) A comparison of the Eyre Pre- Cambrian tract with Archaean 



tracts of the Northern Hemisphere is instituted. In struc- 

 tural composition and petrographical character, the Eyre 

 region bears a striking resemblance to the Laurentian tract 

 of North America, and particularly to the Haliburton- 

 Bancroft area of Ontario. 



