Geology of Mount Macedon. 211 



the Silurian and apparently also on the Cathedral sandstones. 

 The rock is marked on the Survey Map as granite. But it is 

 mercery stalline, and the base shows well marked fluxion. Quartz 

 is abundant, and so also is biotite. There is no hypersthene. 

 The felspar in part shows the minute twinning of anorthoclase. 



In this respect, as in some others, the Cerberean rock is more 

 nearly allied to the Macedon than to the Dandenong dacites. 

 But, speaking generally, the dacites of the Upper Yarra and the 

 Upper Goulburn differ from those of the geburite series by their 

 lower alkalinity and the absence of the minerals riebeckite,. 

 aegerine, and nosean. 



These different dacite masses appear to have similar strati- 

 graphical relations. The Dandenongs, for example, rise above 

 the plain of the Yarra as Macedon rises above its Palaeozoic 

 platform. The dacites have not metamorphosed the sedimen- 

 tary rocks which they overlie. For instance, the Silurians can 

 be seen close to the dacite near the landslip on the road from 

 Mooroolbark to the summit of Dandenong ; the Silurian rocks 

 appear quite unaltered. 



It is true that in some places the Silurians are altered near 

 the junction with the dacite ; but there is no proof that it is the 

 dacite that has wrought the change. It is more likely that the 

 alteration has been caused by intrusions of grano-diorites and 

 porphy rites, which have been injected into the Palaeozoic series.^ 



Mr. Ferguson has stated" that there is a gradual change from 

 the "granites" to the " Dandenong traps"; but I have failed to 

 find evidence of this, and Mr. T. S. Hart, who examined the 

 sections on the Gembrook railway, tells me that wherever the 

 two rocks could be seen together they were both greatly decom- 

 posed. He says there was no sign of a passage between the two 

 rocks. This evidence is consistent with the view that the 

 diorites and the dacites belong to different dates and had inde- 

 pendent origins.^ 



1 Mr. Victor Stirling, it should be noted, has siio:g'ested that the alteration of the 

 Silurian rooks at Lilydale is due to the traps. (No. 21, p. 10.) 



2 He states (3, p. 58) that where the trap and granite join " the one rock merges into 

 the other without a break, the granite gradually getting more and more trappean in 

 character till one rock gives place to the other." 



3 Since the paper was read I have examined the sections in question, and agree with Mr. 

 Hart's conclusions. 



