204 Proceedings of the Royal Society of Victoria. 



predominating structure of the ground mass is granulitic ; hypers- 

 thene is the most abundant ferro-magnesian constituent. 



The typical geburite-dacites form thick dykes. The effusive 

 rocks of Macedon may be divided into four main groups. The 

 first is the geburite-dacite, with hyalopilitic structure, such 

 as occurs around Cheniston. The second group may be called 

 trachy-phonolites ; they are characterised by the abundance of 

 anorthoclase, and the replacement of hypersthene by aegerine ; 

 they probably also occur as dykes. The rock at the Turritable 

 Waterfall is the best type of this group. The rocks of the next 

 group are hyalopilitic with well developed fluxion structure. 

 The minerals are anorthoclase, riebeckite, cossyrite and aegerine, 

 and the rocks may be identified as solvsbergites. Newbery's 

 chemical analysis of the Camel's Hump rock agrees with that of 

 the typical solvsbegites. 



To the last rock of the Macedon series I feel at present 

 doubtful about applying a definite name, not having secured 

 a fresh specimen. The rock is exposed in a shallow quarry at 

 the north-eastern corner of Woodend. It was included by Aplin 

 among the basalts of the Newer Volcanic Series. The rock is 

 no doubt more basic than the other members of the Macedon 

 series, for it contains what appears to be altered olivine. The 

 rock may be left for the present as an alkali-andesite. 



The rock sequence at Mount Macedon, therefore, ranges from 

 holocrystalline dykes of geburite-dacite to a series of effusive 

 rocks including trachy-phonolite, solvsbergite and alkali-andesite. 



The order of the minerals in this rock sequence is well marked. 

 The geburite-dacites contain abundant hypersthene, and some 

 corroded phenocrysts of bytownite. In the trachy-phonolites the 

 hypersthene has been replaced by aegerine, and the basic plagio- 

 clase by anorthoclase. In the solvsbergites the abundance of 

 soda is expressed by the development of the riebeckite and 

 cossyrite in addition to the soda minerals of the trachy-phonolite. 

 The last stage in the series is marked by the occurrence of what 

 is probably altered olivine in the andesites of the northern 

 margin of the Macedon series. 



The foreign rocks most nearly allied to those of Macedon are 

 not found among the dacites, but in the series of i-ocks from the 

 Kristiania district made famous by Brogger's searching investi- 



