412 GEOLOGY AN'D PETROLOGY OP THE GREAT SERPENTINE BELT OP N.S.W., 



Primary tjuartz is very sparingly prest-ut, aud is practically abscut m 1437. Kock 

 1515 is a very ftne-gi-aiued porpbyritic type witbout traebytic arrangement of tbe 

 felspars, and is notable as being tbe only one of tbe series containing bornbleude. 

 Jn band-specimen tbis is seen as fairly al)undant rod-like plienocrysts up to al)out 

 6 mm. in leng-tb. In tbin section it is of a ligbt brown colour and strongly pleo- 

 chroic. In addition to tbe predominant oligoclase of tbe rock, tbere is probably a 

 little orthoelase as small shapeless interstitial grains. Quartz is fairly abundant. 

 Tbe rock (1448) from the Church Hill railway cutting at Currabubula pre- 

 sents some unusual characters. It consists largely of lathy oligoclase showing 

 traebytic fabric, vitb subordinate orthoelase. Locally tbe grainsize of the 

 felspar may increase slightly and its habit may alter to a stout prismatic 

 or to a gi-anular form; this may be due to local variation in the water-gaseous 

 content of tbe crystallizing magma. A large square-shaped section of labra- 

 dorite, comparable with that found in the andesites, may be a xenocryst. The 

 abundant iron-ore is in minut* octahedra, rods and grains, some of it being 

 titaniferous, judging liy the frequent coronas of secondary sphene. Apatite is 

 very scarce. The interesting feature of tbis rock is in the habit and disposition 

 of the quartz, which is present as optically continuous patches, enclosing the fel- 

 spars in micropoikilitie fashion . It also fills what have evidently been drusy 

 cavities, giving a pseudo-porphyritic appearance to tbe rock (PL xxv., fig. 2). 

 In this case the (|uartz, which may consist of two or more grains of different 

 orientations, lias its boundaries determined by tbe felspar-laths forming the ori- 

 ginal walls, which often project into it. This quartz is to be regarded as of 

 primary crystallization; it often contains tiny inclusions and may pass out with 

 optical continuity into the poikilitie quartz. A few of the druses have been filled 

 with opal or with chalcedony, associated with little rosette-shaped bundles of 

 chlorite needles growing on tbe walls of the cavity. One gi'ain of opal includes 

 a granule of ilmenite completely suiTounded by a rim of secondary sphene. 



This rock, being tbe freshest in the collection, was selected for chemical in- 

 vestigation, and the result of an analysis by Mr. H. Yates, B.Sc, is given in 

 the first column of the table. 



T. TI. Til. TV. 



SiOo 07. 71 69.20 71.52 75.06 



AbO:! 15.24 15.00 11.76 14.21 



FeiiOg 1.48 1.57 1.52 1.31 



FeO 1.89 1.83 3.44 0.27 



MgO 0.46 0.60 1.18 0.00 



CaO 3.00 1.88 2.72 0.42 



NaoO 5.87 5.87 5.05 6.88 



K2O 1.81 1.81 0.26 0..58 



H2O+ .. .. 1.89 0.67 1.25 0.62 



H2O— .. .. 0.39 0.00 0.14 0.56 



TiOo 0.47 0..52 0.28 abs. 



PaOr, tr. 0.10 0.20 0.03 



MnO — 0.15 0.04 0.04 



CO2 abs. abs. .38 — 



FeS2 — — 0.12 SO3 0.11 



100.21 100.19 99.86 100.18 



