506 THE CONTINENTAL ORIGIN OF FIJI, II., 



The only other important accessory mineral is apatite, which 

 is sparsely scattered through the rock. Jt is enclosed in all the 

 other minerals, even the magnetite, in small, quite perfect prisms. 



The order of crystallisation of the individual minerals is normal. 

 Considering the amount of mechanical and chemical alteration 

 to which the rock has been subjected, together with the com- 

 paratively high lime percentage of the felspar, it is surprising 

 that so little epidote has been formed. 



Quartz Diorite (Nadranikula, Wainibua, abo\ e the 

 village of Wainiveidro). Plate xxxv., fig. 2. 



As described above, this point was the first point at which an 

 extensive outcrop of plutonic rock was encountered. 



Macroscopic characters.— The rock is, in mass, light grey in 

 colour. It is strongly jointed, there being at least three regular 

 sets of joints traversing it (see p. 474). An additional evidence 

 of strain is afforded by a slight foliation, though this is not so 

 marked as in the Narokorokoyawa rock. 



The grain of the rock is medium, much finer than that of the 

 iSTarokorokoyawa rock. The most obvious minerals are : — Plagio- 

 glase in fairly fresh-looking crystals and grains, 5-6 mm. in length, 

 with very bright cleavage faces and noticeable striation; quartz, 

 interstitial in character; hornblende in quantities quite subor- 

 dinate to the felspar. On the joint-surfaces a greenish to yellow 

 coating of a chloritic substance occurs, with a thickness of about 

 a millimetre. The specific gravity of the rock is 2 70. 



Microscopic characters. — The texture is hypidiomorphic granu- 

 lar. Plagioclase felspar is by far the most abundant constituent. 

 These felspars are highly complex, and their determination is by 

 no means easy. They are more or less idiomorphic in shape, with 

 a <yranular habit. In ordinary light they are seen to be somewhat 

 decomposed, but on the whole are fairly fresh. Zoning is a very 

 marked feature, being indicated by differences of refractive index 

 and arrangement of inclusions. 



Observations in polarised light give rather puzzling results, and 

 appear to indicate that more than one species of felspar is present. 



