BY H. I. JENSEN. 115 



Microscopically it is seen to consist of chlorite and comminuted 

 felspar. Signs of great alteration are wanting. 



There is consequently no evidence on petrographical grounds 

 that the Eumundi and Kin-Kin shales should be considered as 

 old as Gympie. From field investigation it appeared that the 

 former are probably Triassic or later, while the latter are pro- 

 bably older. 



(c) Plutonic Rocks, 



Sp. No.76. Tonalite. Loc : Branch of Delaney's Ok, E. of Black's 

 Hill. 



i. Handspecimen red, on close inspection seen to be made up 

 of red, yellow, white and bluish-black grains, identified with a 

 lens to be orthoclase, plagioclase, quartz and hornblende. 



ii (1) Texture: noncrystalline, medium-grained and moder- 

 ately even-grained, with a hypidiomorphic granular fabric. 



(2) The constituent minerals in order of decreasing abundance 

 may be stated as (a) essential — plagioclase, quartz orthoclase and 

 hornblende; (b) notable — biotite; (c) minute (accessories) — mag- 

 netite, apatite, chlorite, kaolin and leucoxene. 



(3) The plagioclase is hypidiomorphic and varies from acid 

 labradorite to albite. Commonly the exterior of a crystal is 

 composed of oligoclase or albite, while the interior consists of 

 labradorite or andesine. Shadowy extinction arising from this 

 ■decrease in basicity from the centre outwards is very common. 

 Zoning is frequently due to the same cause, but zoning due to 

 the regular arrangement of the innumerable dusty inclusions of 

 magnetite, hornblende and chlorite is also very common. Zoning 

 due to incipient decomposition in the centre of the felspar crystals 

 is also seen. The average composition of the plagioclase felspar 

 would probably be that of oligoclase-andesine. The quartz is 

 wholly allotriomorphic and contains numerous dusty inclusions as 

 well as liquid and stationary gas bubbles. The orthoclase is 

 allotriomorphic and partly kaolinised. It frequently forms a 

 microperthitic intergrowth with albite. The hornblende is of a 

 green colour and pleochroic from olive-green to light yellowish- 

 green. It occurs in corroded phenocrysts and contains numerous 



