﻿Vol. 66.] AND DACITES OF THE DANDENONG DISTRICT. 455 



Three localities will serve to illustrate the relations of the two 

 rocks, which are also illustrated in figs. 2 & 3, p. 456 : — 



(a) A traverse from south to north from the granodiorite between 

 Belgrave and Selby shows first the sharp junction with the 

 gneiss, then a thin belt of gneisses, and farther north a less 

 foliated rock occurs, which appears to pass through schistose 

 dacite into the normal rock. 



(/3) Walking northwards from south of Selby, after passing over 

 a fairly broad belt of gneissic rocks exposed on rising ground, 

 a narrow ridge is reached consisting mostly of foliated gneiss. 

 On this ridge, however, there occurs a small elliptical area, 

 about 20 yards in longest diameter, which consists of normal 

 dacite in the centre and slightly schistose dacite at its margin. 

 Unfortunately, the section is not quite clear ; but within 

 a yard or two there is a change to the foliated gneiss, which 

 is farther north replaced by schistose and then normal 

 dacite. 



(y) A third traverse, in a northerly direction from south of 

 Upway, also shows interesting and puzzling features. The 

 junction of the granodiorite with a schistose dacite occurs 

 immediately south of Honbulk Creek, and is quite sharp. 

 Acid veins traverse the schistose rock near the con- 

 tact. North of Monbulk Creek a pathway rises for about 

 200 yards towards a cottage. Occasional exposures along 

 this path consist alternately of fairly normal dacite and 

 of a highly schistose rock. Several schistose zones appear 

 to be developed in belts trending east and west and 

 roughly parallel to the boundary of the granodiorite and 

 dacite. To the north of these exposures normal dacite 

 alone is seen, except that a quartz-vein about 2 feet wide 

 occurs in the dacite in a cottage garden immediately south 

 of the road from Upway. 



IY. Petrography. 

 (a) The Granodiorite and the Acid Veins. 



The granodiorite. — No special study has been made of this 

 rock. It belongs to the granodiorite group, as defined by Lindgren. 

 This is clear from its chemical composition, and from the fact that 

 the ratio of soda-lime to alkali felspars is more than 2:1. The 

 soda-lime felspars are generally zoned, and range from oligoclase 

 to labradorite in composition. They are usually idiomorphic, 

 especially with respect to the alkali felspar and the quartz, both 

 of which are fairly abundant. The alkali felspar sometimes shows 

 a perthitic intergrowth with albite. The ferromagnesian minerals 

 are biotite (very abundant), and hornblende, which is fairly 

 common near the boundary with the dacite, but appears to be less 

 common away from the junction. It is especially to be noted that 



