232 ON THE GEOLOGY AND PETROGRAPHY OF BATHURST, N.S.W., 



Wood opal, that polishes well, can be collected in some paddocks 

 between the cemetery and Mount Pleasant. Good fire opals are 

 known from Rocky Bridge Creek, where they occur in a decom- 

 posed trachytic lava flow. Good coloured amethysts and rose 

 quartz are frequently brought in from the country between 

 O'Connell and Oberon. 



xn. Conclusion. 



1. Getting results together we find that about Bathurst granitic 

 rocks are extensively represented. 



2. This granite area is surrounded by an aureole of metamorphic 

 rocks. 



3. There is no insensible gradation from a clastic to a holo- 

 crystalline rock, from a sedimentary rock to a granite. 



4. The granite is intrusive as regards the surrounding slate 

 rocks. 



5. Tins is not necessarily opposed to the view that part of 

 the granite may have been formed by a whole or partial fusion of 

 pre-existing sediments. Like the granites of Vancouver, the 

 Bathurst granite is probably at once intrusive and, in a sense, 

 metamorphic. 



6. The silurian slates are the oldest rocks now represented in 

 the district — older than the underlying granites. 



7. The granite comes next in order of time. 



8. The granite rocks underlying the slates are not the floor on 

 which the slate rocks were originally laid down. 



9. This floor has entirely disappeared through sinking within a 

 zone of fusion, or through being absorbed by an ascending molten 

 magma. 



10. Under the microscope the granite is a hornblende-biotite- 

 granifce with a triclinic felspar. 



