BY W. G. WOOLNOUGH. 525 



terminated by symmetrically placed faces, but the angular 

 measurements of these are not sufficient to determine the form 

 definitely. The cleavages parallel to -j 100 }- and -J 010 [- are 

 about equally well developed. The refractive index is very 

 slightly lower than that of the augite, but the difference is very 

 small. The pleochroism is quite strong : 



i^; = light brownish-red. 



b = honey -yellow. 



C ~ light green. 

 The absorption is : a>b>i:5 and is marked. 



The distinction between the two pyroxenes is very pronounced 

 between crossed nicols. Whilst the augite shows colours of the 

 second order, the tint of the hypersthene rarely, if ever, rises 

 above yellow of the first order. The straight extinction of 

 sections in the pinacoidal zones is also a striking feature of 

 distinction. The results in convergent light are far from satis- 

 factory. Where interference brushes are obtained they are 

 nearly straight, indicating an optic axial angle nearty a right 

 angle. In consequence of this, measurements of sign are practi- 

 cally impossible. This feature, and the comparative faintness of 

 the pleochroism, indicate a rhombic pyroxene about intermediate 

 between bronzite and hypersthene. On account of the pleo- 

 chroism, I have called the mineral hypersthene. 



The inclusions in this rhombic pyroxene are similar to those 

 in the augite. 



The only other mineral to be noted is magnetite. This is 

 plentiful in the form of grains up to 0*275 mm. diameter and 

 perfect crystals of somewhat smaller size. 



Hornblende Andesite (Buki Levu). Plate xxxvi., fig. 6. 



The rock here described occurs, in the form of huge boulders, 

 in an exceedingly thick mass of volcanic breccia which builds up 

 the great bulk of the mountains, of which Buki Levu is the 

 centre. The specimens described were collected, not on Buki 

 Levu itself, but on the hill facing it, across a deep narrow 

 ravine less than a mile wide. The base of the breccia is light 



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