404 



W. R. BROWNE AND A. B. WALKOM. 



Under the microscope the rock is hypohyaline ; the base 

 is mostly of glassy material and contains a large number of 

 extremely small felspar microlites. The glassy material 

 is dark in colour, probably on account of the fairly large 

 amount of magnetite distributed in very minute grains* 

 The small microlites exhibit a parallel arrangement, bring- 

 ing out the flow structure present. There is also a larger 

 generation of felspars having a size of about 1 mm. by *5 mm. 

 It is twinned after the albite law and is labradorite. There 

 are a few small grains of another mineral almost colourless, 

 with only very slight pleochroism. Its D.R. is negative 

 and approx. *010 and the R.I. is considerably higher than 

 that of Canada balsam. It has parallel extinction and is 

 biaxial. There seems to be no doubt that it is hypersthene. 

 Magnetite is the only other mineral visible. This rock has 

 been analysed with the following result : — 



Si0 2 



TiO„ 



A1 3 



Fe o 3 



Feb 



MgO 



CaO 



K o 



Na Q 



H 6 H 

 Hlo - 



CO, 



Per cent. 

 58-79 



Moleo. 

 propor. 

 980 



1-21 



15 



17-51 



172 



2-11 



13 



3-87 



54 



2-23 



56 



6-18 



110 



0-68 



7 



4-84 



78 



\- 2-61 





- 0-71 





trace 





100-74 



Quartz 

 Orthoclase 

 Albite 

 Anorthite ... 

 Diopside ... 

 Hypersthene 

 Magnetite... 

 Ilmenite ... 

 Water 



Per cent. 

 . 11-46 

 3-89 

 . 40-87 

 . 24-18 

 . 5-29 

 6-51 

 3-02 

 2-28 

 332 



100-82 



Sal 



80-40 



Fein 17 JO 3 

 Class ii (Dosalane) 



11-46 



F 68-94 5 7 



Order 4 (Austrare) 

 K 2 0+Na 2 85 5 3 

 Cab ~ TTO < 3 > 5 



Rang 3 (Tonalose) 

 K 2 _7 1 

 Na 2 78 7 

 Subrang 5 (Placerose) 



O. Volcanic, (iii) basic. 



Basalt, west of Moogering Creek. 



Dark aphanitic rock with uneven fracture. Tiny lath- 

 shaped felspars can be recognised in hand specimen. 



Under the microscope it is hypocrystalline, pilotaxitic. 

 A small amount of interstitial glass is present in the base. 

 Felspar is present in lath-shaped crystals with their longer 

 axes in a generally parallel direction. Magnetite is abun- 



