president's address SECTION c. 189 



of uplift led to the dissection of this peneplain and the formation of 

 another at a level of only a few hundred feet above sea level, the 

 softer sedunents being easily base levelled, and the more resistant 

 dacites preserving- remnants of the older peneplain. The present 

 surface features of the surrounding sediments are the result of a still 

 later uplift, and the erosion of the sediments consequent upon it. 



Geological Relations (See Plate III., Fig. 1). 

 The relations of the dacites and quartz-poi-phyrites with the 

 granodiorites on the one hand and with the palaeozoic sediments on 

 the other are the chief points of interest, and bear closely on the age 

 of the volcanic series. 



Relations with the Granodiorites. 



Selwpi (39) and the officers of the early Geological Survey ex- 

 j)ressed the view that a gradual passage could in places be traced 

 between the " Traps " (dacites, quartz-porphyi'ites, &c.) and the 

 gianitic rocks, and they regarded them as being intrusive rocks of 

 Palaeozoic age. Professor Gregory (83) maintains that at Macedon 

 they are quite distinct in composition and origin from the grano- 

 diorites, and are quite unaltered near the contact with them. He regards 

 them as volcanic rocks poured out over a denuded Palaeozoic platform 

 of sedimentary rocks and granodiorite, and that in consequence they 

 are far younger than the granitic rocks, and may be of Lower Kaino- 

 zoic age. 



I have been investigating the relations of these two series in 

 Victoria for the past four years, and the evidence I have obtained at 

 the south of the Dandenong Hills, at Warburton, and at Marysville 

 has led me to come to dijfferent conclusions from previous observers. 

 I hope to publish this evidence in detail shortly, and meanwhile 

 piesent a brief summaiy. Mr. Summers (91) has come to similar 

 conclusions on evidence he has obtained in the Strathbogie ranges, 

 while detailed examination of the Macedon district by Mr. Summers 

 and myself affords similar results. The evidence from these areas 

 will be published in detail shortly, while a short summary will suffice 

 for the purposes of this communication. The geological relations of 

 each of the areas mentioned above is, in my opinion, as follows : — 



The Dandenong Hills. — Dacites, quartz-porphjTies, and quartz- 

 porphyrites are represented among the rocks of this area, but it has 

 not been found possible to map the boundaries of each. The rocks 

 appear to be in part intrusive in character, as fairly coarsely crystal- 

 line dacites occur near Aura, on the Gembrook Railway Line. The 

 bulk of them are lava flows, with some pyroclastic rocks. The junction 

 with the granodiorite runs nearly east and west from about 2 miles 

 scuth of Femtree Gully to the railway line just west of Emerald. In 

 1905 I discovered a remarkable belt of gneissic rocks between the 

 normal dacite and the granodiorite, on the Monbulk Creek, South of 

 Belgrave. I have traced this belt for some miles both to the west 

 and to the east nearly to Emerald. It varies in width up to about 

 400 yards. Several junctions of the gneiss with the granodiorite have 

 been found, and everywhere the junction has been quite sharp and 

 distinct. Near the junction in several places pegmatite and quartz 



