Geoloi/i/ of IJIi/i/iilf'. 3^3 



(ii.) The second pair have a sub-alkali LDinpositiori; and art- uaiinMl 

 Lower and Middle Dacite Series respect ivrly. Thev differ cliieHy 

 in the ratio of ground mass to phenocivsts. 



The Middle Series was followed by the Upper oi- Hypersthene 

 Dacite Series, which brought the volcanic phase to an end. 



All the rocks of the system, except the two toscanites, conform 

 U> the same serial curves in variation diagram. Tlie toscanites fall 

 •on curves of their own. The (luestion is, therefore, raised, whether 

 .they should be admitted to the cycle, oi- leferred to some earlier 

 •date. 



Evidence is presented foi- the sites of two eruptive centres, which 

 are marked on the Map. 



Evidence of foliation in the two toseanites, together with its 

 absence from the remaining series is diseussed especially with 

 reference to the Devonian folding movements. 



The dykes are of two kinds, differentiated and undifferentiated. 

 There are signs of radial groupings with reference to some centre 

 in the Dandenongs. 



The undifferentiated dykes appear to be closely associatefl with 

 the plutonic rock, which occurs, on the one hand, about one mile 

 south of the Belgrave railway line, where it outcrops extensively, 

 and, on the other hand, on the eastern slioulder of Mt. Dandenong, 

 where it is invisible. In both cases it has converted the contiguous 

 dacite into a schistose type, and in the latter case, it has also con- 

 verted the Silurians into a hornfels. and has sent out large 

 apophyses, which outcrop in the hornfels below the schistose dacite. 



This residual patch of schistose dacite, resting upon the hornfels 

 is clear evidence of the volcanic nature of the Hypersthene Dacite. 



The type of alteration here is similar to that, described by Piof. 

 Skeats, in the district south of Upwey and Belgrave. 



" The Wandin Dyke " shows a type of propylitization simihu- to 

 that near Hesket (Mt. Macedon), and described by Skeats and 

 ♦Summers. 



In a dolerite dyke near Mooroolbark the groiind mass has been 

 secondarily altered to stilbite. 



4. Evidence is discussed for placing a fault along each of two 

 long uniform junctions, running parallel (X.K. and S.W.) for 

 some distance, one east, the other west, of the Dandenongs. Theic 

 seems little reason to doubt that a great block, including the 

 northern part of the Dandenongs, has subsided between these twn 

 fault-planes. Evidence is presented for another fault — the Olinda 

 iault. 



