286 
Geology of Sydney. 
There is very little evidence to decide the age of 
these intrusions. They were, of course, injected after 
the consolidation of the sandstones and shales, but 
whether in the Mesozoic or Tertiary times it is not so 
easy to decide. It is not unreasonable to assume that 
these dykes are contemporaneous with the basalts of 
Mount Hay and Mount Tomah, which are believed to 
be Tertiary. 
The Mesozoic period generally was one of volcanic 
quiescence in Australia, and contrasted strongly with 
the Palaeozoic period, in which extensive sheets of 
basalts, diorites, and porphyries were poured out, and 
also with the Tertiary period, during which originated 
lavas of a vast extent. We have representatives of 
these Tertiary lavas on Mount Hay, Mount Tomah, 
on the Bald Hills, Bathurst, and in the great basalt 
flows around Orange and Carcoar. 
Granites. 
Granite may be described as a wholly crystalline 
rock, consisting normally of granules of the minerals 
— quartz, felspar, and mica. Very often hornblende is 
also present. These minerals are already described on 
pages 54 and 55. The question, “What is granite?” 
is sufficiently answered in the same chapter. The 
nearest granite to Sydney is that exposed at the base 
of Mount Victoria, around Hartley Vale, but boulders of 
granite have been found near Penrith, carried down 
into the Nepean from the very heart of the mountains. 
Travelling west by rail, the first granite appears beyond 
Rydal, towards Locksley. South of Sydney the first 
