GEOLOGY OF THE GLOUCESTER DISTRICT, N.S.W. 253 



Kuttuog Series and the Gloucester Coal Measures, and 

 there is therefore a strong disconformity between the two 

 series. The Gloucester Coal Measures, so far as the author's 

 observations have gone, appear, except where they have 

 been interfered with by faulting, to conform to the dip and 

 strike of the Kuttung Series and to form part of the same 

 great synclinal fold. It would appear to be the case, there- 

 fore, that the folding which produced this syncline took 

 place after the Gloucester Coal Measures were laid down, 

 i.e., at the end of the Palaeozoic Era. 



Petrology and Rock Analyses. 



A. The Volcanic Rocks. 



Lava flows occur in the Carboniferous System in the 

 Gloucester rocks, both in the Burindi Series and in the 

 Kuttung Series. 



(a) The Burindi Lava Flotvs. — Three lava flows occur 

 in this series, they are all similar to one another in general 

 characters, and are quartz keratophyres. 



No. 1 Flow. — This rock in the hand specimen is light- 

 coloured and aphanitic with moderately abundant pheno- 

 crysts of felspar; in places, however, the rock is quite 

 glassy, and when so is almost black in colour. Under the 

 microscope the groundmass varies from cryptocrystalline 

 to glassy, and in the glassy examples there is an abundance 

 of small rod-like microlites, frequently grouped intostellite 

 aggregates. The phenocrysts consist almost entirely of 

 felspars, a few of these are orthoclase, but the great 

 majority are plagioclase, all are much corroded. The 

 optical character of the plagioclase indicates a variety close 

 to albite. An occasional small phenocryst of a pale green 

 pyroxene is seen, which appears to be diopside, but is too 

 much altered for accurate determination. Occasional 

 small crystals of titaniferous magnetite also occur; inclu- 



