512 THE CONTINENTAL ORIGIN OF FIJI, II. 



portions of the felspar and before the final consolidation of the 

 rock. No other evidence in support of the idea of a secondary 

 addition to the felspar crystals could be found. As will be 

 explained later, abundant evidence of this phenomenon is met 

 with in certain of the andesites; but porphyritic structure, so 

 characteristic of change of physical conditions during the con- 

 solidation of rock, is conspicuously absent in the present instance. 

 I could find no evidence of rounding of the kernels before the 

 crystallisation of the outer coat. 



Inclusions are not ver}^ abundant in the felspar. There are 

 gas-cavities and liquid inclusions with moving bubbles, all of very 

 minute dimensions. Grains and short prisms of a j^ellow-green 

 mineral which, by its refractive index, double refraction, and 

 pleochroism, is seen to be hornblende, also occur. There are also 

 small grains and crystals of magnetite. 



Hornblende occurs in thoroughly allotriomorphic sections up 

 to 2"6 X I'O mm. in area, scattered plentifully through the rock. 

 Cleavage, refractive index, and double refraction are quite normal. 

 The pleochroism is very strong. 



;t = light greenish-yellow. 

 b = dark yellowish green. 

 r = dark green. 

 Absorption : a<b^C. 



The extinction angle c:c = 20^. 



Many of the sections afford fine examples of the ordinary 

 twinning on (100). 



Decomposition has not proceeded to any great extent as a rule. 

 The principal product is a bright green pleochroic chlorite. One 

 patch of this, showing no trace of cleavage, and therefore probably 

 parallel to (001), exhibits in convergent polarised light a 

 sharply curved brush. The mineral is, therefore, biaxial, with a 

 very small optic axial angle ; the optical sign is found to be 

 negative. The pleochroism of this decomposition product is 

 bright grass-green for rays vibrating parallel to the cleavage, 

 light straw-yellow for those at right angles. The double refrac- 



