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THE GEOLOGY OF THE NANDEWAR MOUNTAINS, 



The Differentiation of the Nandewar Rocks. 



A glance at the analyses will serve to show that in the alkaline 

 rocks there is a gradation both mineralogically and chemically. 

 If any one of them can be considered to represent the parent- 

 magma, it must be the pulaskite porphyry, N.ll. 



The phonolites (represented by N.IO, analysed) have almost 

 the same composition as the pulaskite-porphyry. The akerite is 

 a special differentiation-product, the complementary type of 

 which I have not met with. It is nevertheless not far removed 

 from the mean of N.30 (trachyte) and N.12 (labradorite porphyry) 

 given in the above table. In fact it will be easily observed that 

 if that mean be regarded as the composition of the parent-magma 

 (Haupt-magma) the akerite and pulaskite porphyry are comple- 

 mentary forms on either side of it. 



The pulaskite-porphja'y is also interesting as being in chemical 

 composition very near to the trachy-andesites (monzonose) of the 



