132 



clesfield, appear to be somewhat similar to the Blakiston sec- 

 tion, but in reverse order. 



Finally, I beg to suggest that the immense series of 

 rocks of, almost certainly, pre-Cambrian age, should receive 

 a distinctive name. Mr. Howchin has used the name Mount 

 Lofty series for the lower Cambrian rocks to the west of the 

 range, and I propose that the rocks described in the pre- 

 sent paper be grouped as the Barossa series (or "Barossian"), 

 from their extensive development in the Barossa Ranges. 

 Some such name will, I feel sure, be found necessary in deal- 

 ing with the enormous mass of pre-Cambrian rocks in South 

 Australia. I am fairly familiar with rocks of this group in 

 other parts of the State, and, on lithological grounds, I am 

 persuaded that it will be necessary to recognize at least three 

 included series represented respectively by the basement 

 complex rocks of Eyre Peninsula and the islands of Spen- 

 cer Gulf, by the series in Yorke Peninsula typically deve- 

 loped at Ardrossan, and by the rocks I have termed 

 Barossian. 



Petrographical Descriptions of some of the more import- 

 ant Rock Types. 



Rocky Gully, between Monarto and Murray Bridge. 

 Hornhlendic gneiss ^ completely granular, with very uniform 

 grainsize, about '25 mm. on an average. Texture thor- 

 oughly schistose (hornoblastic). Quartz is the most abundant 

 mineral present in rounded and ovoid grains. These are 

 full of little circular flakes of biotite and very numerous 

 liquid and gas inclusions. These cavities are very irregular 

 in shape, and some are comparatively large in size; some of 

 them have ''spirit-level bubbles," others have bubbles show- 

 ing spontaneous movement. 



There is a good deal of albite in perfectly round grains. 

 Most of it is untwinned, but some shows twinning after albite, 

 carlsbad, and pericline laws. Measurements show it to be an 

 almost pure albite. In addition to the albite there is some 

 orthoclase distinguished by its refractive index. Owing to 

 the absence of twinning in much of the albite, it is difficult 

 to estimate the relative abundance of the felspars accurately; 

 the albite is certainly predominant. Both felspars are clear 

 of inclusions. Biotite flakes are fairly abundant, and have 

 very marked parallel orientation. They are intergrown with 

 muscovite, and contain inclusions of magnetite. There is a 

 little muscovite, mostly intergrown with biotite, but partly 

 independent also. Some of the latter is developed across 

 the schistosity of the rock. 



