296 H. S. Summers: 



The name pftanitite, usine it in the English sens© as beinp: a 

 granite having approximately equal amounts of orthoclase and 

 plagioclase, fits the description of this rock exceedingly well, the 

 only objection to the name being that it has been used in more 

 than one sense, and its use therefore is likely to lead to con- 

 fusion. 



Harker does not use the term granitite at all, such rocks as 

 the above being included under the heading of granite. Kemp 

 and Merrill also seem to have dropped the term, while Rosen- 

 busch uses it as meaning a biotite granite, that is, one contain- 

 ing no muscovite. All things considered, therefore, the name 

 granite seems to be the miost suitable for this rock. 



Neither the granite porphyn,' nor the quartz porphyry con- 

 forms to the description of the normal types, as both should 

 contain orthoclase in excess of plagioclase, whereas the bulk of 

 the felspar in both cases, especially the phenocrysts, belongs to 

 the soda-lime series of the plagioclases. Harker divides those 

 intrusive rocks in which quartz phenocrysts are typically absent 

 into porph\Ty and porphyrite according as the dominant por- 

 phjTitio constituent is an alkali felspar, or a soda-lime felspar. 

 Extending this definition to cover the quartz rich rocks, we 

 would get granite>-porphyTite, and quartz porphyrite as the names 

 for the rocks described in this papei\ In the absence of a 

 chemical analysis, however, it is very difficult to estimate the 

 relative proportions of the alkalis to the lime, especially as the 

 grovmdmass is fairly fine grained, so that pending such analyses 

 the names granite porphyry and quartz porphjTy had better be 

 retained. Furthermore, the igneous rocks of this area are dis- 

 tinctly more acid than the main mass of the Strathbogie and 

 Toombullup Ranges, and seem to represent an acid differentia- 

 tion from a grano-dioritio magma, and the name quartz-por- 

 phjrrite would be more suitably applied to som:e of the less acid 

 members of the series, the rocks of this area being an intermediate 

 type between these and the normal quartz-porphyry. 



V. — Age and Rei.ations of the Rocks. 

 The oldest rocks in this area are the sedimentary series 

 which have been sho\\ii to be probably of silurian age. During 

 the deposition of these beds, land surface existed a few miles t-o 



