250 PROCEEDINGS OF SECTION C, 



The felspars are usually clear and slightly zoned with irregular 

 fluid inclusions. Most are well-twinned plagioclase, in one of 

 which, cut at right angles to the brachypinacoid, I found the 

 extinction angles of two adjacent lamellae to be 20° and 21° on 

 either side of the trace of the twinning plane, thus giving an angle 

 of 41°, which, according to Michel Levy's method of determining 

 the plagioclase, would indicate labradorite, or a still more basic 

 felspar. Binaiy twins sometimes occur — in one of them I noticed 

 that one-half was simple, the other polysynthetic. I believe that 

 all are plagioclase. In the Tararu specimen the felspars are 

 entirely decomposed. 



Tlie hornblendes are generally well preserved, and shew the 

 characteristic cleavage pai-allel to 110. They occur in six-sided 

 prisms with the clinopinacoids more or less developed They are 

 occasionally twinned. In ordinary light they are light yellowish 

 brown, but some longitudinal sections are greenish. With polarised 

 light they are strongly pleochroic — and light yellowish brown ; 

 )3 and y dark yellowish brown. The polarization colours are not 

 brilliant, and the angle c : y goes up to 22°. They contain, as 

 inclusions, rather large crystals of apatite, and occasionally they 

 enclose fragments of plagioclase, giving the rock an . ophitic 

 structure. 



Pyroxene has been present in small quantity, but it is now 

 altered into chlorite. 



Chlorite of two kinds is found. The first is of a bright green 

 colour with confused, often radiating fibres, is slightly pleochroic, 

 and with crossed nicols shews an aggregate with low polarization 

 colours. It is found in both the hornblendes and the pyroxenes, 

 and when in the former, encloses large apatite cry.stals. The second 

 kind is a pale yellowish-green, fibrous aggregate, with rather bright 

 polai-ization colours and strongly pleochroic — being bluish-green 

 when the fibres are parallel to the chief section of the polariser, 

 and yellowish-green when they are at right angles to it. This kind 

 is found in small quantity only. The first kind of chlorite, when 

 in the hornblendes, has occasionally been again altered to a 

 colourless aggregate with low polarization colours, and a narrow 

 magnetic border ; this change generally begins near the centre of 

 the chlorite. In the specimen from Tararu no fresh hornblende 

 remains, but its place is taken by a colourless aggregate, a part of 

 which is certainly calcite, surrounded by a black border. 



A little epidote, I think, occurs in some of the decomposed 

 felspars and in the chlorite ; but its presence is doubtful. 



Quartz (original) occurs in angular or sub-angular grains up to 

 about 0.005 inch in diameter, but it is by no means common. It 

 contains greenish belonites and six-sided glass inclusions with 

 fixed bubbles. Sometimes it is corroded and penetrated by the 

 ground-mass, which also appears as more or less spherical inclusions 

 of a greenish-yellow colour. 



