ON THE GEOLOGY OF WEST MORETON, QUEENSLAND. 157 



the Carlsbad law. The refractive index is always less than 

 that of Canada balsam or quartz, and the symmetrical 

 extinctions of the two halves of the Carlsbad twins give 

 readings of 9°. On untwinned sections the extinction is 

 + 10°. In addition to this dominant felspar there is a 

 small quantity of oligoclase in subidiomorphic sections with 

 well marked peripheral outgrowths of anorthoclase in 

 crystal continuity. Quartz is not abundant, it occurs inter- 

 stitially in irregular grains. 



The coloured constituents are subordinate in amount. 

 Augite is in stout prisms, greenish-brown in colour, aver- 

 aging about 0*2 mm. by 0*1 mm., but very many are much 

 more slender. These have a peripheral border of dark green 

 hornblende and very frequently quite considerable terminal 

 extensions of the same mineral. This latter occurs also in 

 independent crystals but not abundantly. 



Scattered through the slide are ragged and subidiomorphic 

 flakes of exceptionally dark brown biotite. The vibrations 

 at right angles to the cleavage give a dark brown colour, 

 those parallel to the cleavage are completely absorbed. 

 There are plentiful thin flakes of ilmenite up to 0*2 mm. by 

 0*01 mm. Apatite is exceptionally abundant in excessively 

 thin needles up to 0*3 mm. In some of the felspar crystals 

 there is a perfect tangle of such fibres. The order of con- 

 solidation is as follows : — 



Apatite , 



Augite 



Plagioclase 



Hornblende - 



Anorthoclase . 



Biotite 



Ilmenite 



Quartz 



