Park. — On some Thames Andesites. 439 



similar hornblende-andesite from a dyke on the shore a little 

 north of the mouth of Tapu Creek, which evidently refers to 

 the dvke at the mouth of the Mata Stream.'* 



AUGITE-ANDESITE. 



A very dense compact blackish-green, almost black, rock 

 cropping out on coast between McCormick's farm and Puru 

 Flat, about four miles and a half north of Thames. Base 

 abundant ; grey-coloured, with microlites of uniform size. 

 Feldspars fresh, plagioclase. not much twinned. Augite 

 fairly abundant ; fresh, with brilliant polarisation colours ; 

 often twinned ; one plate shows marked hour-glass structure. 



Hypersthene-andesite. 



This is a compact dark greenish-grey rock cut 125 ft. 

 north of Queen of Beauty shaft at the Thames, in the north 

 crosscut from No. 11 level, 748 ft. deep. Ground-mass very 

 clear, dusted with magnetite. Feldspars plagioclose ; fresh, 

 but clouded with inclusions ; not much twinned. Hypers- 

 thene often outlined or replaced with black dust ; generally 

 affected with decomposition. No augite detected. 



This rock forms the Exchange bar, one of the best-known 

 bars or undecomposed cores of andesite which traverse the 

 Thames Goldtield, running jDarallel w T ith and separating the 

 main lode systems of the field. At the 748 ft. level it was 

 found to be 60 ft. wide ; in the Exchange shallow level, due 

 north-west, about 90 ft. thick ; and in the 452 ft. level of the 

 May Queen Mine, at a point about 450 ft. north of the Queen 

 of Beauty shaft, 300 ft. thick. Like many of these hard blue 

 bars, it shows a marked tendency to thin out in depth. 



Hypersthene-augite-andesite. 



A compact dark greenish-grey rock, cut last January a 

 few feet from the foot-wall of the Golden Age lode in the 

 Moanataiari Mine, at the 100 ft. level, Point Eussell section. 

 Ground-mass clear, but not abundant. Feldspars plagio- 

 clase ; fresh, often clouded with microlites and glass inclu- 

 sions ; not much twinned ; mostly basic. Hypersthene more 

 abundant than augite ; contains enclosures of glass ; often 

 altered to serpentinous products, and much dusted with 

 magnetite. 



AUGITE-ANDESITE, TAIRUA. 



This is a dense fine-grained rock with a vitreous or glassy 

 lustre and conchoidal fracture. It occurs as isolated frag- 

 ments and large masses weighing many hundredweights on 

 the hills around and south of Tairua Broken Hills Mine, 



* Hutton, Proc. Aust. A*soc. Ad. Sc, 1888, p. 7. 



