524 THE CONTINENTAL ORIOIN OF FIJI, II., 



inclusions, in other cases the great mass of unaltered mineral 

 appears. The solution has certainly had a marked rounding 

 eifect in many cases. 



The phenomenon of secondary addition or rejuvenescence is 

 very obvious in the case of these felspars. In many instances 

 there is a peripheral zone of perfectly clear felspar, of lower 

 refractive index than the crowded portion, perfectly free from any 

 trace of "dusty" inclusions. This zone is obviousl}^ secondary, 

 since it gradually rebuilds the crystal edges of those individuals 

 which had been thoroughly rounded by previous corrosion. The 

 secondary zones contain prismatic inclusions similar to those of 

 the base. Even those sections wdiich do not exhibit corrosion, 

 show by sudden differences of refractive index and double refrac- 

 tion that similar secondary growth has taken place. 



Augite is fairly abundant in broad prismatic sections up to 

 1-7 mm. X 0-9 mm. in size, of a light yellowish-green colour. The 

 prismatic cleavages are strongly developed, but the cleavage 

 parallel to <J 010 [ noted in the Namulowai rock is not developed 

 in this instance, though the crystalline development in the two 

 cases is very similar. Twinning after the ordinar}^ law, i.e., 

 parallel to -j 100 [- is well marked and common. There are also 

 sections showing an intergrowth of augite and hypersthene. In 

 these the hypersthene is inside and the augite outside, the two 

 having the same vertical axis. 



The maximum extinction angle of the augite in sections parallel 

 to -I 010 }■ is 40\ 



The only inclusions worthy of note are grains of magnetite, 

 often idiomorphic, round which the augite exhibits strain-struc- 

 ture. 



Hypersthene is perhaps more abundant than augite ; the 

 .sections are if anything a little smaller, but the difference in this 

 respect is small. The two minerals are readil}^ distinguished by 

 their difference in colour, most sections of hypersthene having 

 a pinkish tinge. The rhombic pyroxene is well developed in the 

 prism zone in which it is bounded by -| 100 [» j 010 [> and 

 -{ 110 [>, all about equally developed. The vertical axis is 



