SQS GEOLOGY OF GLASS HOUSE MTS. AND DISTRICT, 



(1) Green, hard, compact without fragments. 



(2) Red, soft, not unlike a tuff (weathered sp.). 



(3) Dark brown, basaltic-looking. 



(4) Grey, with huge black fragments, and quartz phenocrysts. 



(5) Nearly black, with fragments and quartz phenocrysts. 

 These different kinds of rock all form part of one flow, and merge 



into one another. Some specimens are quite rhyolitic in appear- 

 ance, some trachytic, some dacitic, and some very basic. In some 

 places the lava has developed a pseudo-columnar structure, and 

 has rendered the underlying sandstones columnar. Slides ex- 

 amined show the following constituents to be present in the 

 blackish and commonest type of rock composing this flow : — 



(rt) Felspar. Plagioclase showing fine optical zoning and 

 .shadowy extinction, twinned on the Carlsbad, Albite and Pericline 

 laws, is plentiful. The more basic interior is probably labradorite, 

 and the less basic exterior andesine. Some orthoclase is present, 

 also showing zoning (perhaps anorthoclase). 



(6) Quartz is present in corroded crystals, with glass}- inclu- 

 sions. In some specimens it is very abundant. 



(c) A variety of light green, faintly pleochroic augite in large 

 crystals; extinction angle 3V to 56°. 



(d) Hornblende of two varieties, one of a brown colour with 

 characteristic cleavage, and one green fibrous variet3\ 



(e) Magnetite is present as an accessory, and also a large 

 amount of glass with inclusions and incipient crystals showing a 

 fluidal arrangement. 



( /*) Green chloritic decomposition products are also present. 



((/) Inclusions of trach3'te are present. Some specimens 

 sectioned contain inclusions of a plagioclase trachyte like that 

 of Beerwah, with well marked pilotaxitic texture; one specimen 

 obtained at Mt. Bukay contained an inclusion of Conowrin 

 trachyte. These inclusions are important as affording evidence on 

 the order of eruption of the lavas. 



(k) Black, opaque, angular fragments are also present as 

 inclusions. 



