Basalt. 
265 
Here the sandstones have been altered into the most 
perfect examples of quartzite that are known about 
Sydney. The aboriginals were aware of the nature of 
this stone, and used it to make skinning-knives. This 
quartzite is, in places, stained by iron oxides to a rich 
chocolate brown, and on first sight resembles the iron- 
stained quartz of some auriferous quartz reefs. Even 
miners have been misled by this similarity, and worked 
here for some time sinking and driving. Their efforts 
were not rewarded with any success. In working they 
came on to the hard and undecomposed basalt. A con- 
siderable quantity of this interesting rock is, at the 
time of writing, strewn about the old shaft, but will 
soon disappear before the demands of museums and 
private collectors. 
Between this point and the north head of 
Maroubra Bay seven dykes may be found, varying in 
thickness from one to five feet, all running east and 
west. The rocky headlands to the north and south of 
Maroubra are thus notable for the number of igneous 
dykes that intrude the sandstones. 
In Gentle's quarry, at St. Peters, a dyke now 
represented by decomposed basalt can be examined. 
This dyke is faulted, in two places, by horizontal 
thrust planes. 
When Mr. Wilkinson first drew attention to these 
basaltic intrusions, the public seemed generally much 
interested, and to dispel any possible fears he wrote : 
“ Happily these disruptive agencies have ages ago 
ceased. So that the residents of Petersham, whose 
