208 ON THE GEOLOGY AND PETROGRAPHY OP BATHURST, N.S.W., 



I am not in possession at the present time of sufficient material 

 to deal with this question, but, as a first step towards a solution 

 of the problem, I may state that there is abundant reason for 

 believing that the granite exposed about Bathurst is but a small 

 portion of a very large mass that underlies the palaeozoic rocks on 

 all sides. In keeping with this view, we find that the granite is 

 exposed for a much greater distance up and down the river than 

 across the valley. The lowest rock for miles around is probably 

 granite, and the Bathurst rock shows merely where the overlying 

 beds have been denuded. 



Microscopic Examination of the Granite. — I have made some 

 twenty-five slices of the granite for microscopic examination. 

 Nearly all the minerals of the rock can be seen macroscopically, 

 particularly in polished specimens. Certainly there are fine-grained 

 varieties, but the average Bathurst granite is coarse-grained. 

 Crystals of black hornblende are not unusual of 9 mm. in length. 

 Glistening faces of felspars, 16mm. long, are frequently found. 

 In polished specimens the silica and felspars appear in about equal 

 quantity, or perhaps with felspars slightly in excess. The minerals 

 proved to be present by a microscopic examination are : — 



Essential Minerals. Accessory Minerals. 



Quartz. Muscovite. 



Felspar. Apatite. 



Hornblende. Sphene. 



Biotite. Garnet. 



Magnetite. Calcite. 



Quartz. — Under the microscope, in plain parallel light, the 

 quartz is easily distinguished from all other minerals by its water- 

 clear appearance, the absence of inclusions, and its fresh, unaltered 

 aspect. It is found tilling up the spaces left by the other consti- 

 tuents. Under higher powers, inclusions will be noticed, but not 

 in such quantity as to lessen the contrast between the clear quartz 

 and the cloudy felspars. The hair-like lines that cut through the 

 quartz in every direction fall under the heading of trichitcs, 

 described by various observers. These trichitea can be noticed 



