BASALTS OF BATHURST AND NEIGHBOURING DISTRICTS. 313 
Blayney basalt appears to be quite different in structure from 
either of the others. It is not likely that our basalts have been 
derived from either of these districts. 
At Oberon, there are basalts closely resembling the Bathurst 
rocks in chemical composition, and also not unlike them micro- 
scopically. Swatchfield, in the same district is on the Macquarie 
River system, and, as conjectured by the late Mr. CO. 8. Wilkinson, 
is probably the locality from which our rocks were derived. The 
old lavas probably flowed down the valley of what is now the 
Campbell’s River. The exact centres of eruption have not yet 
been determined. It appears likely that the Blayney-Carcoar, 
the Orange, and the Swatchfield areas formed distinct centres of 
eruption, and the lavas may be of different age. Of the exact 
age there is very little evidence available as yet. They are 
probably late Tertiary, and newer than the present drainage 
system of the country, but beyond that one can hardly speak with 
confidence. 
In conclusion, I desire to express my indebtedness to Mr. A. 
Page, for preparing microphotographs, and to Mr. W. Pascoe, for 
grinding rock sections. 
