908 THE GEOLOGY OF THE NANDEWAR MOUNTAINS. 



All the other analyses are of alkaline rocks. The trachytes 

 from Ningadhun {N.30), Deriah Mountain (N.59), and Dripping 

 Rock (N.55) are very similar in chemical composition, and are 

 also closely allied to the arfvedsonite trachytes of the Warrum- 

 bungles, to my analyses of which attention is directed. They all 

 lie on the borderlines between the subrangs of Phlegrose, Nord- 

 markose, and pulaskose of the quantitative classification. 



The dark sill rocks N.ll (Pulaskite Porphyry), N.IO (Phonolitic 

 Trachyte), and JSr.l2 (Labradorite Porphyry) are of considerable 

 interest. The specimens analysed containing no ealcite, theCOg 

 present is contained in the secondary minerals pseudomorphic 

 after nepheline, namely hydronephelite, liebnerite and geisekite. 

 The Pulaskite Porphyry is in handspecimen almost as dark as a 

 basalt (dark green), and would not be judged to be of very nearly 

 the same composition as the light-coloured trachytes. Micro- 

 scopic examination, however, reveals that the felspar is essentially 

 anorthoclase and microcline microperthite, and that ferromag- 

 nesian minerals are not abundant. The chemical analysis makes 

 the position of the rock still more certain, and the norm fixes its 

 magmatic name as phlegrose, the same as the arfvedsonite 

 trachytes. 



The analysis of N.15 shows that this rock chemically as well 

 as structurally is akerite. 



The altered nepheline phonolite, N.4:9, was analysed because it 

 contained the same doubtful minerals as the corundum-basalt 

 from Billy King's Creek (W.40) in the Warrumbungle Mountains. 

 The analysis suggests that their determination as corundum and 

 laavenite is correct. In the quantitative system this rock has 

 the magmatic name monzonose, and contains quartz in the norm, 

 which differs in a remarkable way from the mode. 



Determination q/PoOg. — This constituent was not determined 

 in any of the rocks analysed from the Warrumbungle and Nan- 

 dewar Mountains, as it was found that utterly unreliable results 

 were obtained. The amount of P-Og in all these rocks would 

 be very small, in those where apatite is most abundant, such as 

 the dolerite (N.17) and the akerite (N.15) reaching a maximum 



N-" 



