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Geology of Sydney. 
CHAPTER XI. 
BASALT, GRANITE AND DIORITE. 
IGNEOUS ROCKS — CLASSIFICATION OF IGNEOUS ROCKS — 
BASALT — BASALTIC DYKES OF SYDNEY— PRISMATIC SAND- 
STONES — DECOMPOSITION OF BASALT — BASALT AT BONDI 
— EXAMINATION OF THE BONDI BASALT : MACROSCOPIC, 
MICROSCOPIC AND CHEMICAL — GRANITE — LA MALADIE DU 
GRANITE— DIORITE. 
It is abundantly clear to tlie reader by this time that 
tlie Igneous or fire-formed rocks stand in marked 
contrast to the Aqueous or water-formed rocks. We 
are no longer dealing with lonely fens, swamps, and 
marshes, or the peaceful depths of ocean waters. 
Instead of the splashing of rivulets or the brushing of 
uncouth reptiles through the tangled undergrowths of 
ancient valleys, we have the roar and thunder of the 
volcano. We must picture the hills lighted up with 
weird fires, and with streams of glowing lava pouring 
over their smirched shoulders and rolling down to the 
lowlands. The evidence is complete that basalt is an 
Igneous rock, and that such basalt-capped hills as 
Mount Hay and Mount Tomah, and the Bald Hills at 
Bathurst, are remnants of vast lava streams which 
