418 GEOLOGY AXD PETROLOGY OF THK GREAT SERPEXTIXE BELT OF X.S.W., 



The Pilotaxitic Type. In band-specimen this is readily distinguished from 

 the lithoidal type by its short, hackly fracture and by the fact that phenocrj'sts 

 are as a rule less abundant. A specimen (1439) collected in the hill in the S.W. 

 part of Portion 100, Werrie, is porphyi-itic in basic labradorite distinctly zoned, 

 but exhibiting rather less resorption than the felspar of the other types. The 

 phenocrysts are generally fresh and contain rare needles of apatite. A very 

 little pyroxene is present, both hypersthene and augite being represented. The 

 proportion of pyroxene among the phenoerj'sts is notably smaller than in the 

 llihoidal.and vitrophjTie types. Little fibrous, pleochroie, purple-brown prisms with 

 feeble birefringence may represent bastitie alterations of the pyroxene. Some ilmen- 

 ite may be included among the phenocrysts. The gToundmass consists of a felted 

 mass of micnilitic felspar, either untwinued or simjily twinned, with a R.I. greater 

 than that of Canada Balsam, and ajiproximately straight extinction. This is 

 probably oligoclase. There is flow structure developed, and interetitial minute 

 granules of pyroxene and iron ore occur, so that the fabric is typically pilo- 

 taxitic. The groundmass is mottled or blotched with ovoid and irregular patches 

 of chlorite enclosing the felspar microlites (PI. xxv., fig. 5) . 



Other examples of the pilotaxitic type showed a general similarity to this 

 rock with occasional minor variations such as the absence of flow structure in the 

 groundmass . 



Lamproplit/re. 



One rock (1450), described as a "felsitie extension of an audesite dyke" in 

 a branch of Upper Currabubula Creek, 5 miles S.E. of Currabubula, belongs 

 to the lamprophyres (PI. xxv., fig. 3). It is pinkish-grej' and felsitie, with a 

 spangled or frosted appearance due to the presence of countless, tiny, rod-like, 

 hornblende crystals never more than 3 mm. in length. I'ndcr the microscope 

 these are seen to be fresh well-formed crystals and microlites, light brown in 

 colour, showing a characteristic cross-fracture and often broken at the ends. 

 Pleochroism is weaker than usual, and there is occasional simple twinning. Some 

 of the larger crystals might be considered plienocrystic; the smaller ones show 

 traces of parallel orientation. A few gTaius of almost colourless pyroxene ap- 

 pear, and others are probably pseudomorphed by carbonates. The groundmass 

 contains, in addition to hornblende, much-altered acid felspar, with a plentiful 

 sprinkling of magnetite and a little apatite. A vei-y abundant constituent is a 

 zeolitic mineral, similar to that found in the quartz keratoph^Te of Clmrcli Hill, 

 which acts as a kind of matrix to the other minerals over irregular small areas, 

 and fills the central portions of cavities, which may sometimes be lined with tiny 

 quartz-prisms. 



This rock is possibly allied to the kcratophyres, but the habit of its eon- 

 stittient minerals would place it rather in tlie lamprophyre group. 



Basic Intrusive Rocks. 



There is a great variety of basic intrusive rocks developed in the Currabubuhi 

 district. They occur for the most part widely distributed throughout the area as 

 dykes intrusive into the Kuttung Series. An interesting series of basic dykes 

 is also found in close connection with the Warragundi centre, intersecting the 

 Wenie Series. So great is the amplitude of the textural and mineralogieal 

 variation in these rocks tliat it is difficult to conceive how thev all emanated from 



