PRESIDENT S ADDRESS SECTION C. 



185 



The Rocks of Frenchman's Hill, Omeo. 

 Geographical and Geological Relations. 



This area lies just to the North of Omeo township, in Eastem 

 Oippsland. Between two confluents of Livingstone Creek there i*ises a 

 somewhat abrupt hill to the height of 500 ft. above the level of the 

 streams. It is locally known as the Frenchman's Hill. The only 

 published description is by Howitt (57). The geological sequence, 

 according to him, is as follows : — The oldest rock is a mica-schist. 

 Intrusive into this are ma,sses of quaortz-diorite, followed by granites, 

 aplites, felspar quartz dykes, quartz felspar dykes, and quartz veins. 



Subsequent in age to these are the intrusive rocks of Frenchman's 

 Hill, which differ in structure and comjjosition from the granites, but 

 are regarded by Howitt as a later part of the same plutonic series. 

 In addition to the main mass there are two apophyses or dyke-like 

 masses which extend westwards across Livingstone Creek. A number 

 of dykes also radiate from the central mass. Although these 

 apophyses are regarded by Howitt as intrusive rocks, the geological 

 raap published with his paper suggests the possibility of their being 

 lava flows. In a short visit which I made to the district in company 

 with Dr. Howitt, this view was strengthened by the evidence seen in 

 the road cutting where the larger tongue-like mass from the hill 

 crosses the road. The rock is here trachytic in character and 

 apparently fragmental, suggesting to me either a coarse trachytes-tuff 

 or a lava flow crowded with fragments, while Howitt interprets it as 

 due to movement before final consolidation. The evidence as to the 

 age of these rocks is not very satisfactory. It is clear that it is the 

 youngest igneous rock in the district, but how much younger, it is 

 than the granite is not evident. In view of its petrological and 

 chemical similarity to the trachytic rocks of Macedon, its grouping 

 with the Devonian volcanic rocks must be regarded as tentative only. 



Petrological and Chemical Characters. 



The rocks are all pale in colour, and vary considerably in texture. 

 Near the top of the hill they ai-e fairly coarsely porphyritic and more 

 plutonic in appearance, except that a distinct ground mass is present. 

 Away from the centre of the hill the texture is finer and more 

 trachytic, while the radial dykes are very fine grained. All the rocks 

 are described by Howitt as '" Orthophyres," and the porphyritic felspar 

 identified as orthoclase. Six analyses were made by him, three of 

 which are recorded here. , 



