Petrology of the Silurian Sediments. 49 



by the fact that the plagioclase occurs in two conditions. The pre- 

 sence of biotite and chlorite supports the view of an igneous origin 

 for part of the sediments. 



The strain polarisation of some of the quartz may have been 

 produced, not in situ but in an older sediment. Our known Ordo- 

 vician rocks have suffered much greater stresses than the Silurian. 

 All the quartz does not show strain polarisation. 



The Ordovician sediments of Victoria have not yet received any 

 attention petrologically. When they ai-e examined they Avill prob- 

 ably show the presence of much similar material to that of the 

 Silurian. An Ordovician quartzite section in the writer's posses- 

 sion shows zircon and tourmaline. 



In conclusion the writer wishes to gratefully acknowledge the 

 invaluable help and guidance of Professor Skeats through all stages 

 of the work, and to Dr. Summers for various suggestions. 



