184. 



These igneous rocks have altered the surroundirig sedimentary 

 strata ; sandstones are baked into quurtzite, shales into lydian 

 stone, and either may be brecciated, as at Bondi and Dundas. 



The white clay resulting from the decomposition of the igneous 

 rocks can be sometimes used as kaolin. In a case of this character 

 at Gosford the iron from the dyke has concentrated upwards, and 

 has formed a capping of good limonite. 



Sioecimens to he found near Sydney : — 



Jlinerals. In the Sandstones — 



Barytas, very rarely. 



Carbonate of lime, in coatings. 



Coal, in small seams, in many places. 



JFelsjJar, decomposed. 



Gariieis, very small and scarce. 



Gold, very rarely seen as free gold. 



Graphite, in small scales. 



Jasper, pebbles. 



Mica, in small scales. 



Pyrites. 



Quartz, frequently showing some traces of crystal faces. 



In the Shales — 



Calcite, Chert, Ironstone, Glauconite (Balmain shaft), Mica, 

 Native Copper, and Carbonate of copper staining, have been 



found on fossil- wood in a tuffaceous bed of the Narrabeen 



Series, at Long Keef. 

 Magnetite, as grains in a tuftaceous bed at Long Eeef. 

 Fyrites. 



Zircon in sand at Long Eeef. 

 Vanadium-staining in certain clays.* 



In the Igneous Eocks. 



As primary constituents — 

 Analcite. 



* On weathering', these clays may show a green colouration. Buildings built of bricks 

 made from them ha^'e had to be washed with acid to remove the stainjthus produced. 



