408 GEOLOGY AND PETROLOGY OF THE GREAT SERPEXTISE BELT OF X.S.W 



All these constituents are compacteil together and set in a biMJwn-stained un- 

 resolvable matrix containing uiuiierous tiny cliii>s of (|uartz, felspar ami pumiceous 

 glass . 



I>iterbedded Floas ami Tnjjs in the Kutluiig Series. 



(a) Suda rhyolites and tuffs. luterbedded with the Kuttung Series are what 

 appear in the iield to be rhyolitii- tlows or tuffs. Thc.'se form a series of striking 

 outcroi^s on the right bank of Rocky Creek in Portion 322. Three specimens 

 have lieen sectioned and examined, and they prove to be soda rhyolites or soda 

 rhyolite tuffs. The rocks are fragmental wholly or partly, but it is not clear from 

 a microscopic examination whether they should be classed as tuffs or essentially 

 massive volcanic rocks with a gi-eat deal of tuffaceous material included . 



1493 from the east end of Portion 273, Currabubula. is in hand-specimen a 

 light gi-eyish-green rock with a dull felspathic-looking gTuundmass containing small 

 phenoerysts of felspar and quartz. Under the microscope the (|uartz is seen to 

 be fragmental and much corroded, as is also the felspar which is pure albite of 

 the variety known as checker-albite . The groundmass is largely crypt ocrystalline, 

 is free from tiow-structure, and in addition to little gi-ains of felspar and quartz, 

 contains large numbers of remains of collapsed pumice in the shape of little cus- 

 pate bodies now devitritied and represented by strings of chalcedonic (|uartz 

 granules and little prisms of clear albite. There are also little irregular pockets 

 consisting mostly of granules of clear secondary albite. A few vei'y small 

 rounded vesicles are tilled with the chalcedonic quartz and chlorite. 



1534 from Portion 322 is a green, hard, dense lithoidal rock recalling in a])- 

 peai'ance some of the Pokolbin rhyolites. There are phenoerysts of (|aartz up to 

 1 ram. in length, originally idiomorphic but now much shattered and corroded, 

 and with inlets and inclusions of groundmass; also fragments of pure albite up 

 to 2 mm . long and a good deal shattered . The groundmass consists of small 

 chips of quartz and felspar and numberless pumice fragments, set in a crypto- 

 crystalline base in which there are occasional streaks of glassy material. A little 

 apatite is present. Tlie groundmass (if the rock contains inclusions of rhyolitic 

 rock, the largest being of fluidal fabric, and poryphyritic in quartz, orthoclase, 

 and albite. 



Specimen 1535 (PI. xxv., fig. 1), descril)ed as a "llnw bi-eccia fi'om Portion 

 322, Currabubula," looks more distinctly like a. tuff than cither ol' the others in 

 hand specimen; it has a hard stony base of pale green colour, in which can he seen 

 tiny fragments of quartz and of white and pink felspar, as well as larger dark- 

 coloured inclusions of rock. The microscope shows it to be composed of abinulant 

 small fragments of quartz and felspar and deviti-ified pumice with chips of fluidal 

 and spherulitic rhyolite, set in a eryptocrystallinc base containing little nests of 

 secondary (|uartz. The quartz fragments are angular and corroded; felspar com- 

 prises albite and orthoclase, the former ])redominating and both a good deal de- 

 composed. The rhyolitic inclusions are sometimes much chloritized. and the flow- 

 lines are indicated by strings of secondary (juartz granules. What a|)pear to 

 have been cavities are now lined with tiny prisms of clear (|uartz and filled with 

 a colourless zeolitic (?) substance stained in jiatches with haematite. 



(h) Basaltic Rocks. In Portions 57 and 5!), Currabubula. there is a small 

 flow (1407) of peculiar type (PI. xxv., fig. 7) . In hand-specimen the rock is dark 

 greyish-brown and aphanitic, with a very few small felspar phenoci-ysfs showing. 

 Microscopically felspar is the only fresh constituent, in laths about 6 ram. long, 



