Geology of Mount Macedon. 213 



Mesozoic, we may hope to find fragments of the Dandenong 

 dacites in the South Gippsland coal measures. If it be found 

 tliat there is no trace of the dacites in these deposits then the 

 eruptions of the Macedon- Dandenong series are probably later 

 than the Lower Mesozoic. 



At present the evidence that gives the most plausible sugges- 

 tion as to the approximate age of the Macedon eruptions is the 

 association of the dacites and the basalts. 



The basalts are now divided into two groups. The Newer 

 Volcanic Series, the Pliocene of the Geological Survey, is 

 Upper Cainozoic, and probably lasted till the human occupation 

 of Victoria. The Older Volcanic Series, the " Miocene " 

 of the Geological Survey, is probably Lower Cainozoic, and 

 according to Messrs. Hall and Pritchard may have begun in the 

 Cretaceous. 



The great dacite eruptions are probably connected with the 

 beginning of the Older Volcanic series. Some of the rocks 

 which Aplin mapped as Pliocene basalts belong to the group 

 which he mapped as Palaeozoic traps. To get an independent 

 opinion on this point I showed Mr. E. T. Prior a thin section of 

 the rock from the quarry north-east of Woodend, telling him it 

 was mapped by the Victorian Survey as basalt. After a brief 

 examination he expressed the opinion that the rock was evidently 

 related to the Macedon series and was not a basalt. 



I had come to this opinion in the field, and have not yet been 

 able to determine the line of separation between the lavas of the 

 Macedon series and the basalts. This close field association, 

 therefore, suggests that the two igneous series are not so z'emote 

 in age from one another as was thought. 



It is probable that Mount Macedon was formed at the 

 beginning of the great series of eruptions which ended in the 

 formation of the great basalt plains of Victoria. It is not 

 uncommon for a great period of volcanic activity to begin with 

 the formation of lofty piles of lava belonging to the intermediate 

 group and to end with the discharge of broad sheets of either 

 acid or basic rocks. The volcanic history of the Yellowstone 

 Park furnishes a classical illustration of this sequence. As 

 Professor Iddings (10) has shown, a long period of quiet sedi-. 

 mentation, which lasted through the Palaeozoic and Mesozoic, 



