Victorian Igneous Rochn. 267 



It must be admitted that these recalculated analyses do not truly 

 represent the composition of the different types, as there is no allow- 

 ance made for the presence of ferric iron or magmatic water ; but 

 still the above result must be considered significant. 



If we use the term " unit molecular concentration " to indicate 

 the sum of the molecular ratios, then in the case of the Macedon 

 granodiorite-dacite series the unit molecular concentration remained 

 constant throughout the various stages in the differentiation of these 

 rocks. It will be seen later that there is apparently a relationship 

 between the molecular concentration and the shape of the variation 

 curves. 



(b) Victorian Upper Palaeozoic Series. 



Besides the rocks of the Macedon area, analyses have been made 

 of other dacites, granodiorites, etc., belonging to the Upper 

 Palaeozoic of Victoria. 



Several analyses of rocks from the Dandenong and Healesville 

 district were made some years back at the Mines Department 

 Laboratory, but the methods used were such that too much reliance 

 cannot be placed on the results. 



In 1908 Mr. H. C. Richards (12) analysed the dacite from near 

 Upwey, in the Dandenong Ranges, and this analysis compares very 

 closely Avith those of the Macedon dacites. 



Thanks to the courtesy of Mr. E. J. Dunn, late Director of the 

 Geological Survey of Victoria, several analyses of granitic rocks 



