182 W. N. BENSON. 



occurs in individual grains. It is in very small amount 

 however. Nepheline does not seem to be present in any of 

 the slides I have examined. 



Two extreme types call for special notice. The exceed- 

 ingly coarse-grained rock illustrated in Plate 7, is composed 

 of large crystals of augite up to two centimetres in diameter, 

 with smaller crystals of olivine and plagioclase. There are 

 also small crystals of ilmenite and apatite. Between the 

 large crystals is a little fine-grained ground-mass composed 

 of tiny felspar laths, some of them possibly sanidine, and 

 pale yellow-brown masses of a platy zeolitic material, the 

 precise nature of which must be left for future examination. 

 Here and there are aggregates of very minute graphic 

 crystallisations and rods of brown-grey augite of the second 

 generation. This is very similar in many respects to the 

 augite that is intercrystallised with the nepheline of the 

 rocks described above. The rock must provisionally be 

 classed as a porphyritic olivine dolerite. The same name 

 is to be applied to a rock of a very different appearance, 

 namely, that figured in fig. 3, Plate 6. It consists of large 

 phenocrysts, up to 4 millimetres in diameter, of augite and 

 olivine, set in an almost basaltic ground-mass composed of 

 abundant small grains of ilmenite and purple augite with 

 felspar laths. A little of the yellowish zeolite is present, 

 and a very few small olivines. There appears to be a third 

 generation of minute brown-grey arrow-heads and needles 

 of pyroxene developing interstitially. 



The only definitely nephelinic rock yet found near Nundle 

 is that from Square Top. It forms a capping two hundred 

 feet thick on the summit of the hill, but its mode of occur- 

 rence was not proved. There were apparently no underlying 

 Tertiary gravels. In hand specimens the rock is dark grey, 

 with dark purple-brown augites, and on weathered surfaces 

 white felspar laths can be distinguished. Its microscopical 



