Geology of Mount Macedon. 209' 



The section (Fig. 4) shows a transverse section across Mount 

 Macedon ; but owing to the denseness of the forest and scrub 

 only a diagrammatic section is at present possible. 



The original crater must have been far above the present 

 summit of the mountain, which may once have risen 5000 feet 

 above the underlying Palaeozoic platform. It is now only the 

 basal stump of a volcano, in which all traces of the crater 

 have been lost, but which has not yet been sufficiently dissected 

 to show the rock of the central core. 



VIII. — Allied Eruptive Centres in Victoria. 



Before considering the place of Mount Macedon in the volcanic 

 history of Victoria it will be convenient to refer to the distribu- 

 tion of allied igneous rocks in the State. 



Rocks rich in soda are widely distributed here both in time 

 and place. Mr. Howitt has described (6, p. 38) an orthophyre 

 from Omeo with 7'12 % of soda; the rock is assigned to the 

 middle palaeozoic. 



Petrographically the Victorian rocks most closely related to 

 the gebui'ite-dacites are some dykes traversing the Ordovician 

 beds at Bendigo. They were originally described as limburgites, 

 and have been referred by Miigge to the monchiquites. I have 

 not been able to see the slides described by Mr. Howitt, from 

 the 180 Mine; but some dykes collected at the Eaglehawk Mine 

 are monchiquites, though in places rendered abnormally acid by 

 the infiltration of secondary silica. The only certain fact as ta 

 the age of these dykes is that they are post-Ordovician ; but Mr. 

 Howitt has suggested that they are in all probability connected 

 with the Cainozoic basalts. Petrographically it is probable they 

 are of the same age as the Macedon eruptions. 



The Victorian rocks with which the Macedon series is most 

 allied geologically are the great eruptive masses of the Upper 

 Yarra and the southern tributaries of the Goulburn. The 

 masses in question are formed of dacites and constitute the 

 mountains of Dandenong, the Cerberean Range, the Blacks' 

 Spur, near Healesville, and possibly an independent centre 

 between Mount Arnold and Warburton. 



