510 THE CONTINENTAL ORIGIN OF FIJI, II., 



The Other accessory minerals are the small, relatively long 

 pi-isms of apatite noted above as inclusions in the later formed 

 minerals, and an occasional very small zircon. 



With regard to the order of crystallisation, magnetite encloses 

 apatite but is earlier than sphene. All three are earlier than 

 hornblende, felspar, or quartz, which crystallised in that order. 

 The crystallisation of the felspar referred to anorthoclase over- 

 lapped that of quartz to some extent, as the two are found inter- 

 grown in a semigraphic manner at times. 



D i o r i t e (Gravels of Navua River at Nakorowaiwai). 



Macroscopic characters.— The rock is moderately coarse-grained. 

 It is greyish in colour, and is speckled with hornblende. It 

 consists principally of greyish felspar and very dark green horn- 

 blende; some biotite can also be recognised. Quartz is not veiy 

 noticeable on the rolled surface, but on the polished surface is 

 seen to be moderately plentiful. The greenish decomposition 

 products of the hornblende and biotite are fairly abundantly 

 distributed. Specific gravity 2-79. 



Microscopic characters. — The texture of the rock is moderately 

 coarse hypidiomorphic granular. 



The constituent minerals include triclinic felspar, hornblende, 

 biotite, a little interstitial quartz, small amounts of magnetite 

 and minor accessories, and decomposition products. The rock is 

 therefore almost a pure diorite. 



The minerals as a whole are surprisingly fresh-looking, though 

 the ferromagnesian constituents show signs of incipient decompo- 

 sition. A certain amount of strain is evidenced by the fracturing 

 of the felspars, bending of the micas, and undulose extinction in 

 most of the minerals; but the absence of marginal crushing shows 

 that the forces have not been very intense. 



Felspar is the most abundant constituent of the rock. It 

 occurs in idiomorphic and subidiomorphic sections averaging 

 about 2-3 by 1'25 mm. in area. It is quite clear and colourless, 

 and, though much cracked, is free from decomposition products. 

 The usual cleavages are strongly developed. A study of the 



