420 GEOLOGY AND PETROLOGY Or THE GREAT SSRPEXTINE BELT OF N.S.W., 



flow strupture, while others are more or less opliitif. Gralu-size is uiediuni to fine. 

 Jliueralogieally they consist of plagioclase, augite and iron ores, but there is much 

 variation in the relative proportions of these constituents. In the porphyritic 

 rocks the felspar of the phenocrysts is usually a zoned basic labradorite, while 

 that of the groundmass is acid labradorite to andesine. The felspar of the non- 

 porphyritic tyjies is labradorite about Ab40 Anno. Most of the rocks ha\e suf- 

 fered considerable alteration, which is best exhibited by the ferro-magnesian 

 minerals, now largely- represented by iiralite, chlorite (pennine), epidote and 

 carbonates. Iron ores are plentiful, both ilmenite and magnetite having been 

 identified, while in one rock a little pyrites was noticed. Primary quartz is a 

 very minor constituent in a few of the rocks. 



One type should be noticed, although its field relations have not yet been 

 completely determined. It occurs as a dyke in the Warragundi complex, and is 

 unusually coarse in grain, the felspars often attaining a length of 12 mm. Un- 

 fortunately the specimens so far obtained have proved vei-y difficult to section, 

 but still the rock has been determined as belonging to the gi-anophyric diabases 

 or quartz dolerites, a small amount of interstitial mieropegiuatite being visible 

 here and there, the felspar of which is an acid plagioclase in optical continuity 

 with the zoned large crystals. Normal augite, much uralitized, is apparently the 

 only pyroxene. Skeletal ilmenit-e and some apatite complete the list of con- 

 stituents. The occurrence of this fiuartz dolerite is interesting, inasmuch as a sill 

 or other intrusion of gTanophyre occui-s not far away, which microscopical ex- 

 amination proves to be composed almost entirely of quartz and albite. The asso- 

 ciation of quartz dolerites and granophyres or aplites. particularly of sodic type, 

 has been noted in various parts of the world, and a genetic connection has in many 

 eases been proved. This fact adds to the interest as well as to the complexity 

 of the Werrie volcanic series. 



(h) Dolerites characterised hi/ Acid Pkir/ioclase. Two specimens of this typo 

 were collected, the first (1451) from the narrow dyke through the conglomei'ates in 

 C.L. 3,000, Currabubula. A close-grained, dark greenisli-brown rock, in thin 

 section it is flue-grained and non-porphyritic, and of distinctly basaltic aspect 

 (PI, XXV., fig. 8) . It is composed of subidiomorphic laths of albite averaging 

 about .3 mm., cleai' and fresh, tiny augite prisms, and' magiietite in crystals and 

 skeletal forms. The interspaces are occupied mostly by brownish chloritic ma- 

 terial forming at least 30 % of the section, and possibly representing an original 

 intersertal glassy base. The suspicious clearness of the felspar miglit be taken 

 to point to albitization. The rock may be termed a fine-grained Albite Dolerite. 



Of a generally similar character is specimen 1492, from ''a dyke through the 

 Church Hill felsite in the railway cutting li miles west of Currabubula." This 

 is a dark-coloured, compact, basaltic-looking rock . lender the microscojie tliere 

 are seen to have been two periods of crystallisation, the older felspar being in 

 elongated laths averaging about .(5 mm. These are very much clouded with 

 decomposition products, so that optical determinations are difficult, but there is a 

 symmetrical extinction of 10" and the R.I. appears to be a little less than that 

 of Canada Balsain. so the mineral is probaldy acid oligoclase. No ferro-magnesian 

 minerals are present, but there is a good deal of chlorite, and there are abundant 

 tiny granules of secondary sphene. Ilmonife and magnetite are very plentiful in 

 little octahedra, and in rod-like and skeletal forms. There is in places a meso- 

 stasis consisting mostly of microlitic plagioclase with magnetite dust and chlorite. 



