Victorian Igneous Rocks 295 



hand, fault iiiir would >iivt' rise to L-li;unuds \i\> whirli the more 

 deeply-seated i^asie portion might tind a passage to the surface. 

 In cases where folding and faulting have accompanied one another 

 Tve might be expected to get an a.ssoeiation of the two types, and in 

 such a case hybrid rocks caused Vjy the mixing of portions of the 

 two magmas might be expected to occur. 



VII. Summary. 



The aim of the present paper has been to discuss the relationship 

 of certain Victorian igneous rocks and to see what deduction may 

 be made from such study. 



The differentiation of several series has been treated at some 

 length, especially with reference to the use of variation diagrams, 

 and it has been shown : — 



1. Variation diagrams constructed from analyses which have 



been recalculated to 100 per cent, with the water omitted 

 and with all the iron converted to ferrous oxide give a 

 better representation of the serial relationship of a group 

 of rocks than diagrams constructed from original analyses. 



2. There is an apparent relationship between the shape of the 



variation curve of the total molecular ratios and the shape 

 of the curves, indicating the serial relationship of the 

 rocks. Thus in the Victorian Upper Palaeozoic series the 

 variation of the total molecular ratios of the recalculated 

 analyses (i.e., the molecular concentration) can be ex- 

 pressed by straight lines, and the variation of the oxides 

 may also be expressed by straight lines. On the other 

 hand the variation of the oxides in the Macedon Kainozoic 

 series must be expressed by means of curved lines in agree- 

 ment with the curvilinear variation of the molecular con- 

 centration. 



3. The conception of the complementary diffeientiation of 



certain of the Macedon alkali rocks is upheld by the mole- 

 cular concentration cuive. A similar type of differentia- 

 tion probably accounts for the origin of certain of the 

 Upper Palaeozoic series occurring at Lilydale. 

 The limits of the differentiation of the Victorian Upper Palaeo- 

 zoic series are discu.ssed at some length, and it is found that the 

 theoretical acid limit value is a bimineralic compound consisting 

 approximately of 39 per cent, quartz and 61 per cent, alkali 

 felspar, and that the theoretical basic limit value, if we neglect 



