196 president's address — section c. 



I have not had an opportunity of seeing these rocks in the field, 

 but have examined some of Howitt's rock sections from Moore's 

 Crossing. In my opinion the sections show that the rocks have a 

 typical andesitic structure and that several varieties are present. 



Those which I have seen include biotite-andesites, hornblende- 

 andesites, enstatite, and augite-andesites, and some of the less basic 

 members have characters which ally them to the trachyandesites. 



UPPER PALEOZOIC. 



Upper Devonian or Lower Carbonitehous. 



Geograjohical and Geological Relations. {See Map, Plate 4). 



Two areas of volcanic rocks referable to this age occur, the one 

 in Eastern the other in Western Victoria. The eastern area com- 

 prises a mixed series of acid and basic rocks developed near Mount 

 Wellington, with a subsidiary area further east. The western area 

 consists of acid rocks developed near Hamilton and Cavendish, and 

 another area near Balmoral. 



The Mount Wellington area. (See Section, Plate II., Fig. 2). — - 

 The volcanic rocks of this district as shown on the map consist of a 

 narrow band of rocks stretching northwards from Ben Cruachan in 

 the county of Tangil past Mount Wellington to the Snowy Bluff. 

 North of Mount Wellington a western tongue of similar rocks runs 

 southwards for some miles parallel to and a little to the east of the 

 valley of the Macallister Eiver. The rocks consist mainly of a 

 considerable thickness (up to 2,000 ft.) of acid lavas, rhyolites and 

 quartz-porphyries with minor interbedded flows of a basic rock 

 described by Howitt as melaphyre or basalt (43, 48, 59). The whole 

 series is interbedded with the Upper Palaeozoic sediments which stretch 

 from this district north-westwards to Mansfield. The field relations 

 are described by Murray (46) and Thiele (89, 90). The bifurcation of 

 the area of volcanic rocks north of Mount Wellington appears to be 

 due to the fact that all the rocks are bent into a shallow anticline, 

 the axis of which to the south has been denuded, exposing older rocks 

 beneath. In consequence of this folding the volcanic rocks show 

 steep scarps on the inner sides of the fold where the crown of the 

 anticline has been dissected (89, 90). The country is a rugged and 

 moimtainous one, and Mount Wellington rises to a height of 5,360 ft. 

 About 10 miles east of Mount Wellington is the northern part of the 

 outcrop of a similar series of acid volcanic rocks which stretches 

 southwards for about 12 miles to the headwaters of IgTiana Creek. 



The age of 'these rocks is determined by the fossil contents of 

 the sandstones and mudstones with which they are interbedded. 

 Lepidodendron australe is found near the Avon River and Cordaites 

 occurs at Iguana Creek, while northwards near Mansfield fish remains 

 occur which have been referred to the Lower Carboniferous. Cordaites 

 is generally regarded as U. Devonian in age, while the Lepido- 

 dendi'on is known both from this horizon and the L. Carboniferous. 

 The age of the rhyolites and melaphyres is thus either U. Devonian 

 or Lower Carboniferous. 



The Western District areas. — The volcanic or intrusive rocks of 

 these areas have been partially described and their areas delimited 



