192 Proceedings of the Royal Society of Victoria. 



In some vai'ieties of the rock from this plutonic mass horn- 

 blende is present, and it sometimes wholy replaces the biotite. 

 The hornblende occurs in patches, in some of which it is fairly 

 abundant. In the rock as a whole, however, the presence of 

 hornblende is exceptional. 



This plutonic rock was mapped by Aplin as granite, an identi- 

 fication supported by Selwyn, who described (19, p. 7, No. 51) it 

 as a "binary granite." But the rock is allied to the diorites by 

 the abundance of plagioclase and the scarcity of orthoclase. lb 

 is a typical member of that series of Vicorian plutonic rocks that 

 have been described by Howitt {e.g., 7, p. 31) and accepted by 

 Rosenbusch (17, vol. i., p. 231) as quartz-mica-diorites. The 

 rock is sometimes a quartz-amphibole-diorite. 



The rocks of this series differ from the typical European 

 quartz-mica-diorites, e.g., that of the Val Camonica, in the nature 

 of the felspar. The alkali felspar is far more abundant than in 

 the true diorites, which are characterised by the predominance- 

 of the basic felspar. The Victorian rocks are intermediate 

 between the normal granites and diorites. We may therefore 

 conveniently adopt for them the name of grano-diorite, which 

 has recently been widely used in America for the similar rocks 

 of the Sierra Nevada. 



The preceding description of this grano-diorite is necessary, 

 because a passage from it to the "traps" of the Macedon series 

 has been generally maintained. Murray, for example, states 

 (14, pp. 22, 23) that "in all these instances [i.e., Macedon, 

 Dandenong, and Healesville] there seem to be no clearly defined 

 lines of demarcation between the rocks classed as trap and the 

 adjacent granites, while in some places a gradual passage from 

 one to the other, as regards mineral composition, is observable, 

 and the diflerent forms appear to blend with one another as 

 though they were simply rocks of varying mineralogical structure 

 belonging to the same general mass." 



However, I could find no trace of passage from the plutonic to 

 the eruptive rocks. Half a mile south of Cherokee the two rocks 

 can be seen close together. Both present their normal characters 

 up to the junction. The comparatively coarse grained quartzose 

 rock underlies the compact dark green Macedon rock, and neither 

 Mr. Grayson nor myself could find any intermediate variety. 



