NOTE ON COPPER IN ANDESITE. 53 



pliides, the order of crystallisation would depend on the 

 laws of fusibility. In this case the felspar would separate 

 out first being the most infusible. For these reasons it 

 seems highly probable that the copper ore of Lautoka owes 

 its origin to magmatic differentiation, but if not its origin 

 is duo to magmatic extraction in the lava. As far as can 

 be judged from my specimens and information which I have 

 received, the bornite is not an inclusion snatched from 

 deep seated plutonic sources. 



Petrological Note.— In view of the comprehensiveness of 

 Dr. W. G. Woolnough's petrological descriptions of Fijian 

 rocks, it will be unnecessary for me to give any detailed 

 descriptions of slices of specimens sent to me, which in most 

 respects agree in petrological characters with the porphy- 

 ritic andesites described by Dr. Woolnough. The minerals 

 most abundantly represented in the Lautoka andesites are: 



(1) Felspar — this mineral occurs in most of the rocks in 

 two generations. The phenocrysts consist of labradorite 

 having a maximum extinction angle of 26° - 27° in sym- 

 metrical sections. They are usually twinned on the 

 Carlsbad plan and frequently possess albite twinning as 

 well. Pericline twinning is also but more rarely repre- 

 sented. Zoning is strongly in evidence, and is of two kinds. 

 (a) due to inclusions, and (b) due to interlamellation of two 

 kinds of felspar. Usually both kinds of zoning are present 

 in the same crystal. In several cases the centre, an inter- 

 mediate zone, and the exterior have been observed to 

 extinguish together at a lower angle than the two zones 

 intervening. The edges of the phenocrysts are generally 

 corroded. The second generation of felspar consists of 

 lathshaped microlites of a more acid felspar, such as ande- 

 sine or oligoclase-andesine. 



(2) A light green feebly pleochroic augite having the 

 same colour as the hornblende and rhombic pyroxene. 



