BY THE REV. J. MILNE CURRAN. 227 



2. (Slide 48). Large twins of augite can be detected without 

 the use of the microscope, their yellowish-brown colour contrasting 

 with the other almost colourless minerals of the slice. Under the 

 microscope the greater number of the lath-shaped felspars show 

 incomplete terminations. A few small olivines are seen altered 

 completely to a light green serpentine. Many other patches of a 

 like green secondary product, that show no definite boundaries, 

 originated in the same way. All the magnetite seems a primary 

 constituent. A few large augites show lines of uncertain inclusions 

 just inside their boundaries and parallel to the outer edges of the 

 crystal. With inclined Nicols, faint traces of zones can be 

 detected. There is very little glassy matter. 



3. (Slide 9). Under the microscope, shows the general structure 

 of the Bathurst basalt. Porphyritic crystals of augite, olivine and 

 plagioclase, set in a much finer ground mass of the same minerals, 

 with cubes of magnetite abundantly developed. The felspars flow 

 round the augites, but are not seen to penetrate them, so there is 

 no arrangement approaching to the ophitic structure. Patches of a 

 light red isotropic body are seen set in the dark hemi-crystalline 

 base. It is probably glass. The large compound augite has 

 some inclusions of the same material. The augite contains well 

 marked cubes of magnetite as inclusions. The olivines are seen 

 cracked in directions evidently independent of the cleavage lines. 

 They are also somewhat corroded along their outer edges. 



The microscopic structure of the basalt is so uniform along its 

 length in the field that the above descriptions may be taken as 

 fairly typical of the whole. 



Chemical composition of the Basalt. 



Specific gravity at 18'5° C 2-63-2-75 



Silica , 44-67 



Alumina 21*38 



Ferric oxide 2-82 



Ferrous ditto 5-99 



Lime (Ca 0) 10-24 



