73 



of silica is present in the divitrified base together with some 

 of the alumina. Analysis II., which has been inserted for 

 comparison from Western Australia, shows an interesting 

 analogy, most of the constituents agreeing closely, with the 

 exception of alumina and lime. This particular rock contains 

 phenocrysts of augite, felspar, olivine, and a little quartz in 

 a ground mass of plagioclase and altered glass. 



Chemical Diagrams. 

 The following diagrams have been employed to facilitate 

 the comprehension of the chemical analysis : — 



Na 2 



flgO 



fll 2 3 



CaO 



The Mugge Diagram. 

 CaO 



SiO 



The Brogger Diagram. 



