160 rroceedings of the Royal Society of Victoria. 



porphyrites, have the characters of intrusive rocks. In various 

 parts of the series there are diabases which have the structures 

 of lavas, though the material is now entirely altered. Photo- 

 graph Knob, South Heathcote, consists of one of the most 

 interesting rocks in this series ; it has the characters of a 

 volcanic agglomerate. Hence, especially at South Heathcote,. 

 some of the diabases are of eruptive and volcanic character. 



V. — Age of the Heathcotian Series. 



According to the view which has hitherto prevailed, the- 

 Heathcote series is of postsilurian age. In that case the rocks 

 of the diabase series are intrusive into the silurians. 



(A). — Relatiofi with the Si/uriafi. 



The first evidence against this view is the complete absence 

 of any contact alteration along the line of junction of the diabase 

 and Silurian series. Where they are in close juxtaposition the 

 Silurian rocks have not been baked. Lidgey has already quoted 

 the occurrence of pebbles of the metamorphic rocks in the 

 silurian ; and the microscopic examination of the basal silurian 

 rocks at the Copper Mine shows that they contain a considerable 

 pi'oportion of diabasic material. These facts clearly show that 

 the silurian is later than the Heathcotian series, and is resting 

 u neon form ably upon it. 



(B). — Relations with the Ordoviciaii. 



The relation of the ordovician and eruptive rocks is less clear. 

 As a rule the junction is somewhat obscure ; and I have not 

 attempted to follow it all along the line. I have examined 

 typical sections where the ordovician and the dial)ase series occur 

 in contact, and in some cases found no evidence of contact 

 alteration. In places, as at Red Hill, the diabase series is 

 separated from the ordovician rocks by a band of schists,. 

 and I liave not been able to find any sharp junction between 

 these schists and the overlying ordovician beds ; but, on 

 the other hand, I have not been able to see any passage from the 

 schists into the ordovician beds. I have in no case been in 



