320 
schists, and mica schists. The whole region has suffered consid- 
erable regional metamorphism, in common with the metamor- 
phism shown by the eastern beds of the Mount Lofty Ranges 
on the mainland. The differentiation of contact and regional 
metamorphism for e ea 1 consideration would 
demand much careful field and petrographic study. 
III. CHARACTERS or THE Rock Tyres. 
(a) THE MAIN GRANITE. 
iron pyrites can be detected in some specimens. Under the 
microscope the minerals developed are seen to be quartz, 
Quartz occurs, firstly, as subidiomorphic grains with well- 
developed cracks, and showing undulose extinction. These 
represent the grains seen in hand specimens. Minute 
, gain, some of the quartzes when carefully examined 
.... Show zones of alternate clear and opalescent layers in reflected 
. . ight, and, in transmitted light, these show up as colourless 
. and yellowish areas respectively. zones appear to 
follow the outlines of the growing crystal. D5^—2650. It 
ot proposed to consider this question in the present paper» 
the subje b is reserved for a subsequent communication. 
