BY H. C. RICHARDS. 189 



The curves for combined soda and potash are good 

 curves, and both the alkaline and sub-alkaline curves are 

 somewhat above the normal. The trachyte from Cainbable 

 Creek, which on general considerations is regarded as 

 belonging to the sub-alkaline series, is rather richer in alka- 

 lies than the others of that series. The third series of rocks 

 again takes up an intermediate position. Curves for 

 phosphorus pentoxide, titania and manganese oxide have 

 not been drawn up. 



After an investigation of these variation diagrams, it 

 is clear that the rocks of the area belong to three series, 

 an alkaline series, a sub-alkaline series, and a third series 

 intermediate between these two, also that the rocks of the 

 area as a whole are a little higher in both soda and potash, 

 and a little lower in both lime and magnesia, than the 

 normal, and although the alumina is low and the total 

 iron-oxides are high, the combined oxides of aluminium 

 and iron are normal. 



The Alkaline Series. 

 The rocks of this series are from the Glass House 

 Mountains, Flinders Range and the Main Range. There 

 are eight analyses, and all are those of Dr. Jensen. These 

 rocks form perhaps 5 per cent, of the volcanic rocks of 

 this area, which has been generally regarded as one rich in 

 alkaline eruptives. 



The series ranges from acid to sub-acid and is much 

 more restricted in that respect than the other series. It is 

 particularly rich in alkalies and rather deficient in lime 

 and magnesia, when compared with the alkaline rocks as a 

 whole ; but this is to be expected to some extent as alkaline 

 volcanic extrusives are, in general, more salic than the 

 equivalent plutonic types. 



The occurrences are somewhat scattered and separated 

 from one another. Dr. Jensen has dwelt on the fact that 

 these alkaline rocks have been poured out near the junc- 

 tions of the Palaeozoic and Mesozoic formations. This is in 

 general true, but we have had apparently similar conditions 

 of folding, faulting and position with regard to Mesozoic 

 coastlines &c., for both the alkaline and sub-alkaline 

 series. 



