182 



GEOLOGY OF SYDNEY. 



Two show-cases have been set apart on the southern wall to 

 illustrate the geology of the Sydney District. 



The rocks between Lake Macquarie and Clifton, and. between 

 Sydney and the Blue Mountains, consist of shales and. sandstones, 

 dipping slightly so as to form a sort of basin beneath Sydney, 

 and intruded in many places by dykes of igneous rock. These 

 rocks contain a few fossils which prove them to be o£ Triassic 

 age — that is, they overlie the Coal Measures, and all the Palaeozoic 

 strata and older rocks to which valuable m6tals are generally 

 confined. Could a deep bore be put down at Sydney, after 

 passing through the Coal Measures, which have already been 

 proved to exist, the older Devonian and Silurian rocks would 

 be found. This order of strata will be better understood on 

 reference to the table on page 17S. 



Sedimentary The beds coming to the surface near Sydney are in descending 



Eocks. -, 



order : — 



"Wianamatta Shales. 

 Hawkesbury Sandstones. 

 Xarrabeen Beds. 



Wianamatta Shales. — These constitute the fruit-growing 

 soils of Hornsby, Parramatta, and Liverpool. They are used 

 for brick- and pottery-making at St. Peter's and elsewhere; 

 occasionally, too, they contain fireclays. They are frequently 

 micaceous. The junction between the Wianamatta shales and 

 the underlying sandstone may be seen in railway cuttings in the 

 northern suburbs — near Carliugford, for instance. The junction 

 is an irregular one, the surface of the sandstone evidently having 

 been very uneven when the shales were laid dowm, as mud, on 

 top of them. 



Hawkeshury Sandstone. — A sterile sandstone, friable when 

 first exposed, often forming a magnificent building stone, for 

 which purpose numerous quarries have been opened at 

 Sydney. When cut through by running water, it forms the 

 magnificent headlands and precipitous cliffs and escarpments so 



