210 Proceedings of the Royal Society of Victoria. 



A description of a few of these rocks will illustrate their 

 affinities to the Macedon series. 



iVIount Dandenong consists of a hypersthene-biotite-dacite. The 

 •quartz is more abundant and occurs in larger phenocrysts than 

 in the gebux'ite-dacite. Biotite is also more abundant. Hypers- 

 thene occurs in large corroded phenocrysts, and there are rare 

 crystals of augite. The predominant felspar is apparently 

 andesine. The base is granulitic. I have not found any trace of 

 aegetine or riebeckite in this or any other of the Dandenong 

 rocks examined. An analysis prepared by Mr. Jenkins shows 

 that the rock is normal in alkalinity. This rock appears to form 

 the main mass of the Dandenong hills, and it is associated with 

 tuffs of the same mineral composition. 



The Blacks' Spur, between Healesville and Narbethong, is 

 another dacite dome. A specimen from the summit of the 

 ridge has been analysed by Mr. Jenkins, and the results show 

 that the rock has a very similar composition to the Dande- 

 nong dacite. The microscope shows that the petrographic 

 •characters are practically identical. 



At the northern foot of the Blacks' Spur the dacites rest on 

 grano-diorite. In order to test whether there be any passage 

 rocks between the two, I have examined the rocks nearest to the 

 junction that I could find. 



A small quarry at the bend of the road close by the gateway 

 to Mr. Lindt's house, the Hermitage, is the most convenient 

 type of the dacites near the grano-diorites. The rock is much 

 decomposed. It consists of abundant quartz phenocrysts, which 

 ■are deeply embayed by the ground mass ; there are numerous 

 flakes of biotite altered to chlorite, and of a pyroxene broken up 

 into chloritic aggregates. The base is a weathered glass, which 

 shows well marked fluxion structure. That the rock was flowing 

 in a thick viscous condition is indicated by the fragments of 

 fractured crystals remaining close together. 



The rock is a weathered lava and is in no way intermediate 

 between the dacite of the summit of the Blacks' Spur and the 

 grano-diorite. 



The Cerberean Range is also composed of dacite. I have only 

 been able to examine the north-western edge of this mountain ; 

 but there it consists of dacites resting on an iri'egular surface of 



