208 president's address — section c. 



NEWER KAINOZOIC TO RECENT. 



Newer Basalts. 



Geographical Distribution. (See Map, Plate 4). 



The youngest volcanic rocks of Victoria consist of a series of 

 basic lavas and fragmental rocks having a considerable geological 

 range and a wide geographical distribution. They form the Melbourne 

 and Keilor Plains, they occur in the Ballarat and Smythesdale areas, 

 over large areas of the Lodden Valley, and some thousands of square 

 miles in the Western District passing over into South Australia, and 

 connecting with the recent volcanic rocks of the Moiuit Gambler 

 district. 



Physiographical and Geological Relations. (See Section, 

 Plate III., Fig. 2.) 



The outpourings of lava and eruptions of fragmental rocks have 

 largely obliterated former inequalities in surface relief over the areas 

 in which they occur. The readjustment of drainage led to swampy 

 conditions, and the filling of swamps in low-lying depressions has 

 over extensive districts given the area the character of a monotonous 

 plain (6). It is diversified by few features. Brecciation of the lava 

 flows by flow during final stages of consolidation has produced the 

 ■' Stony Rises." A sharp scarp-like line runs N.W. from west of 

 Station Peak, and another occurs near Bacchus Marsh. This may 

 represent a feature formed by denudation and not obliterated by the 

 lava flows, or it may represent a fault scarf foraied during the 

 eniptive period. It separates an elevated plain from a low-lying 

 one of 50-100 ft. less altitude. The more impressive relief features 

 are of two kinds. In the one case, the basalt flows occur in areas of 

 considerable relief and only fill up the low ground, so that the older 

 rocks in places rise as islands above the general basalt level. Some- 

 times these islands are of the lower Palaeozoic sediments, in other 

 cases, as in the You Yangs, between Melbourne and Geelong, they 

 consist of bold granitic hills. 



The other eminences in the basaltic plains are the volcanic 

 hills which are scattered in profusion over the area, and which 

 present examples of volcanoes in all stages of dissection and disinteg- 

 ration. Some apparently undenuded hills show no signs of a crater, 

 and their appearance suggests a simple heaping up of lava above 

 some orifice, or above the point of intersection of fissures. Hills like 

 Mount Franklin, near Daylesford, and Mount Noorat, are examples 

 of recent volcanoes with weU-preserved craters. Mount Franklin is 

 breached on the eastern side. 



Tower Hill, west of Warrnambool, is an illustration of one of the 

 most recent of Victorian volcanoes. It is a good example of a caldera 

 with a lake in the enlarged older crater, and more recent craters 

 built up within the enlarged crater ring. Almost horizontal tuflfs 

 build up the mass of the hill. Near Camperdown lavas and tuSs are 

 interbedded, but more generally the last materials forming the cones 

 consists of pyroclastic material — i.e., agglomerates, scoria, and tuffs. 



