﻿Yol. 66.'] AND DACITES OF THE DAXDEN0NO DISTRICT. 453 



(b) The Altered Dacites. 



In most places in Victoria where the junction of dacite and 

 granodiorite has been observed, the dacite, for a few feet from, 

 the junction, commonly shows a slight tendency to a schistose 

 character, and, as will be seen subsequently, this is accompanied by 

 interesting mineralogical changes revealed under the microscope. 

 At Macedon the junction is of this character, and also at jSyora and 

 probably near Marysville. 



For a considerable distance along the contact in the Dandenong 

 area the contact-rocks of the dacite series are of the above character. 

 This is the case to the south-west of Upway, and also in the 

 district between Selby and Aura and for a little distance east of 

 Aura, where the dacite, besides being slightly schistose, is much 

 coarser in grain and approaches somewhat closely to a plutonic 

 rock in habit and texture. 



(c) The Gneissic Rocks. 



South of Upway, Belgrave, and Selby, at and near the junction 

 with the granodiorite, a remarkable series of gneissic rocks is 

 developed. This can be traced eastwards to a point south-west 

 'of Aura Station, where its place is taken by the coarse-grained and 

 but slightly schistose dacite already mentioned. Farther east, 

 between Aura and Emerald, the gneissic rocks are seen once more. 

 In places the rocks are typical gneisses, being very well foliated. 

 The planes of foliation are approximately parallel with the junction 

 of the granodiorite. Biotite, quartz, and felspar appear to be the 

 constituent minerals, and a considerable variation in texture, from 

 fairly coarse-grained gneisses to fairly fine-grained schists, is 

 noticeable in the field. 



(d) Relations of the Granodiorite to the Altered Dacite 

 and to the Gneissic Rocks. 



The exact junction between the granodiorite and the gneissic 

 rocks, owing to limited exposures, cannot everywhere be seen. 

 The area is well wooded, and at the point where the gneisses were 

 first seen the junction with the plutonic rock could not be found. 

 I at first thought that the foliated gneiss might be a modification of 

 the granodiorite produced by differential movement at its margin 

 during the later stages of consolidation. Further examination of 

 that part of the contact which lies between and south of Belgrave 

 and Selby provided definite evidence that this view of the origin of 

 the gneisses must be abandoned. In many places between these 

 limits the actual junction could be seen to be perfectly sharp and well 

 defined, and several junction -specimens have been collected. The 

 granodiorite examined in the heart of the mass is a quartz-biotite- 

 felspar rock, with hornblende and basic patches occasionally 

 developed. It shows no trace of foliation, and retains these 



