582 THE CONTINENTAL ORIGIN OF FIJI, II. 



Augite of the first generation is fairly plentiful, though not 

 to the same extent as felspar, in broad prisms up to 1-25 mm. 

 long by 0-75 mm. wide, scattered irregularly through the base or 

 grouped in nests of more or less intergrown crystals. The colour 

 is light greenish-yellow. The prismatic cleavages are perfect, 

 and the rather unusual cleavage parallel to the clinopinacoid (at 

 right angles to the trace of the twinning plane) is developed here 

 as it is in the Xamulowai rock. There is nothing remarkable 

 about the refractive index or double refraction. The highest 

 extinction obtained in the vertical zone is 41'^. Judging by the 

 amount of curvature of the hyperbolic brush in convergent 

 polarised light, the optic axial angle is not large. The augite 

 contains as inclusions crystals of magnetite and also minute 

 colourless prisms about 0-025 mm. long, whose refractive index is 

 not very different from that of the augite. These prisms exhibit 

 straight extinction and weak double refraction, and may be apatite. 

 Gas- and glass-inclusions are moderately abundant up to 0*06 mm. 

 in diameter, but mostly much smaller than this. The smaller 

 glass-inclusions have the form of negative cr3^stals and contain 

 fixed bubbles. Though, on the whole, the augite is perfectly 

 fresh, here and there patches of brownish serpentinous mineral 

 are met with. 



There are comparatively scarce areas throughout the rock 

 which represent pseudomorphs after hornblende. Most of these 

 are irregular or rounded in shape, but a few of them still preserve 

 the typical outline of a cross section of hornblende and thus 

 afford the key to the explanation of the more irregular ones. 

 They all contain very abundant magnetite; in many cases this 

 mineral constitutes almost the entire bulk of the pseudomorph. 

 In other cases, however, there is adn^ixed with the magnetite 

 more or less perfectly clear and colourless pyroxene. This rock 

 therefore indicates an intermediate stage between the pyroxene 

 andesites of Xamulowai and Voma, and the typical hornblendic 

 andesites of Korobasabasaga and Korowaiwai. 



Magnetite is fairly plentiful in irregular grains up to 0-3 mm. 

 diameter and smaller idiomorphic crj'stals. 



