BY H. C. RICHARDS. 149 



These trachytes are represented by the leucocratic and 

 melanocratic varieties, though the light-coloured varieties 

 are the more abundant. The leucocratic varieties are light 

 grey to bluish grey in colour, and range from holocrystalline 

 to holohyaline; while the fabric may be trachytic, micro- 

 granitic, or orthophyric. There are little or no soda-lime- 

 felspars, but one finds sanidine. soda-sanidine and 

 cuiorthoclase. The matrix minerals are a;girine, riebeckite, 

 arfvedsonite ; olivine and biotite do not occur. The melano- 

 cratic varieties are dark grey or brown in colour, and are 

 usually less porphyritic than the leucocratic types. 



The texture varies from holocrystalline to holohyaline, 

 and the fabric may be almost pilotaxitic, although generally 

 it is trachytic. The felspars are orthoclase, anorthoclase, 

 microperthite and lime-soda-felspars. The matrix minerals 

 are a>girine, augite, magnetite and ilmenite. 



Glassy varieties of the trachytic rocks are not so 

 abundant as those of the rhyolitic rocks, but at Mount 

 Flinders there is a very tine trachytic glass which Jensen 

 has described, also at Cainbable Creek there is a dull green 

 trachytic pitchstone associated with the trachyte. 



Specimen 128. — Locality : Cainbable Creek, portion 12, 

 parish of Nindooimbah. This is a greyish rock in the 

 hand-specimen. It is holocrystalline and slightly porphy- 

 ritic. The phenocrysts, which are frequently anorthoclase, 

 occur as sub-idiomorphic crystals up to 1-5 mm. in diameter. 

 The groundmass is orthophyric and is made up of short 

 stout prisms of sanidine and occasional crystals of pale 

 augite. Abundant granules of magnetite occur all through 

 the section. The rock has been considerably altered, and 

 limonite and chlorite are abundant. The chlorite and some 

 of the limonite are the result of alteration of the granules 

 of pyroxene which are distributed through the rock; some 

 of the limonite is also derived from the magnetite. Small 

 patches of a secondary carbonate, probably calcite. occur 

 through the rock. The specific gravity is 2-40, and this 

 low value is no doubt due to the somewhat cavernous nature 

 of the rock. Name: Orthophyric Trachyte. 



Specimen 129. — This is from the same locality as the 

 previous rock, and is a somewhat mottled greenish-grey 



