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Charles Fenner: 



igneous intrusions have turned these beds into hornt'els or spotted 

 elates, as exen)plified in the Werribee Gorge area, but such altera- 

 tion is not considerable. 



The present total thickness of these Ijeds is unknown. In the 

 Bendigo gold field similar rocks were penetrated to a depth of 4600 

 feet, and proved of the same character throughout. We may sum 

 up this most important series of rocks as being extremely and 

 almost uniformly resistant to erosion. (Throughout this paper the 

 term *' Ordovician " refers to these lower Oi-dovician l)eds.) 



(b) Granites and Granodiorites. — The nature of the plutonic 

 intrusive masses, regarding their lesistance to erosion, is well 

 known. Granite forms the great mass of the You Yangs, whose 

 highest point (Station Peak) still i-ises like a pyramid 1154 feet 

 above sea level, and over 800 feet above the basalt and alluvial 

 surrounding it. Towards the Anakies this granite is much Avorn 

 down, and remains as low hills capped by huge residual tors. The 

 only granodiorite exposed is a small area in the Werribee River, 

 between Bacchus Marsh and Ballan. It assists in forming the 

 rugged and precipitous "Werribee Gorge." On the surface it 

 proves no more resistant than the rock (Ordovician), which it in- 

 trudes, and presents a fairly level surface of somewhat clayey and 

 gritty soil, 



(c) Permo-Carhoniferous. — These rocks consist here of glacial 

 ■conglomerates and sandstones, and present some differences in their 

 powers of resisting erosion. They are foi- the most part either level 

 bedded or gently dipping, and grade from very coarse conglomer- 

 ates down to almost uniform fine sandstones. Their investigators 

 state that rocks of this age had a variety of origin- — glacial, fluvio- 

 glacial, and probably lacustrine. In places the rocks are much com- 

 pacted and indurated, as at the mouth of Werribee Gorge, where 

 they occur in part as steep cliffs. 



At other points we get friable sandstones, giving us rounded 

 grassy hills, and wide U-shaped valleys, as in the lower Korkuper- 

 rimul (Lyell's Creek) and Bald Hill at Bacchus Marsh. The 

 higher parts of Bald Hill, especially Avheie the dip of the beds is 

 most marked, present a very barren appearance, bare rocks being 

 exposed over large areas. All the extensive outcrops of glacial are 

 wdthin the let-down Block B, except a few which have been similarly 

 preserved in the N.W. corner of the relatively depressed block E. 

 In the north of block B, we also get both types, the very . hard 

 rock giving up the high bluff near Glenpedder homestead, and the 

 more friable material providing the pleasant rounded hills of- 



