190 Proceedviigs of tlie Royal Society of Victoria. 



In 1895 Mr. R. A. F. Murray (14, pp. 22-23) accepted the 

 name of syenite porphyry and advanced the view that this rock is 

 intimately associated witli the <^ranites which occur below it. 



The last contribution to the geology of Mount Macedon is a 

 paper by Mr. E. G. Hogg (5, pp. 93-96), in which the rocks of 

 the Turritable Creek waterfall, the Camel's Hump, the Hanging 

 Rock and Brock's Monument are determined as trachyte. Hogg 

 expressed the opinion that the age of the Macedon rocks is 

 almost certainly post-Silurian, and probably later than the Permo- 

 Carboniferous, owing to their absence from the glacial conglom- 

 erates of that period. 



IV. — The Petrography of the Macedon Rocks. 



Most of the Mount Macedon ridge is covered by gum forest, 

 thick scrub, and a mantle of deep, rich soil. Rock exposures are 

 scanty and small ; accordingly a detailed geological map is impos- 

 sible, and the determination of the relations of the various rocks 

 by field evidence is disappointingly difficult. Hence it will be 

 convenient to reverse the normal order of procedure, and describe 

 the petrography of the Macedon rocks before dealing with their 

 relations in the field. 



The igneous rocks of Mount Macedon may be divided into 

 six groups : — 



1. Grano-diorites 



2. Geburite-dacites 



3. Trachy-phonolites 



4. Solvsbergites 



5. Andesites 



6. Agglomerates and Ashes. 



The rocks of the last five groups are those properly belonging to 

 Mount Macedon ; the association of the rocks of the first 

 group is accidental, as they belong to the underlying Palaeozoic 

 platform. 



The following descriptions of the rocks are limited to features 

 of geological significance. An account of the mineral constituents 

 I hope to issue subsequently. 



