part 2] OF SOUTHERN EYRE PEISTINSULA. 127 



Dr. Stillwell further describes types in which the pyroxenes 

 become partly replaced by hornblende, and these present many 

 features in common with No. 89 of the Lincoln Series. 



No olivine has been recorded from these Antarctic dolerites, and 

 no appeal has been made to an olivine-felspar interaction for the 

 synthesis of garnet. 



As presenting features intermediate between the metamorphosed 

 dolerites and the pyroxene-amphibolites already described, several 

 basic bands of which hornblende is an important constituent, from 

 Boston Island and the coast immediately south of Tumby Bay, 

 call foi- description. The constituents are hornblende, plagioclase, 

 granulitic augite, and hypersthene, with minor and varjdng amounts 

 of quartz, orthoclase, apatite, and iron-ores. A foliated structure 

 may be imparted by a rude parallelism of hornblende ; but, on 

 the other hand, granoblastic textures are common. The original 

 igneous character of these rocks is indicated by the presence of 

 occasional blastophenocrysts of felspar, or blastoglomeroporphyritic 

 aggregates of the same mineral. 



No original augite is present, the pyroxenes being of the granu- 

 litic secondary type. Much of the hornblende can be regarded as 

 derived from pyroxenes in situ, but there is also represented a type 

 which by its shape and attitude must have been crystallized as 

 such. 



As seen in the field, these rocks preserve quite well-defined 

 boundaries with the enclosing gneisses. Several junctions have 

 been studied microscopically. 



The gneiss at the junction shows a granulitic texture, with 

 occasional phenocrysts of orthoclase and plagioclase, which may be 

 aggregated at the border-line. The component minerals are quartz, 

 orthoclase, plagioclase, and grains of hypersthene. The attitude 

 of these pyi'oxene grains is noteworthy : along the border of the 

 basic band is a concentration of the pyroxenic grains, and enclosed 

 within the gneiss are aggregates and isolated grains of the same 

 mineral. These show all the characters of being mechanically 

 derivable from the basic band, representing xenoliths broken off 

 the basic rock. If we accept this view, the metamorphism has 

 been accomplished as a thermal effect of intrusion, and the 

 secondary granulitic p^Toxenes observed near the junction of the 

 basic rock with the gneiss represent a derivation from the basic 

 band itself. 



IX. Comparison of the Flinders Series w^ith the Eocks 

 OF other Pre-Cambrian Areas. 



In drawing attention to features displayed in other Pre-Cambrian 

 tracts — of similar type to those met with in the Flinders gneisses 

 of Southern Eyre Peninsula, it will suffice to remark on a number 

 of areas in the Northern Hemisphere. 



