234 Charlps Fenner : ' 



The grades of the Djerriwarrh, Toolern, Boggy and Condon'a 

 creeks have been carefully plott-ed in Plate XTIB. An inspection will 

 show that they clearly tell a story of rivers rejuvenated in their 

 upper reaches. The lower five miles or so of these streams show a 

 gentle rise of 100 feet to the mile. At the point where other physio- 

 graphic evidence suggests a fairly well-dissected scarp line, these 

 streams rise 500 feet in a mile — a grade five times as steep as that 

 below; thence to the top of the highlands the grade is less steep, 

 giving us a line of the nature shown in Fig. 25. This is a quite 

 similar line to that of the Lerderderg and Werribee, due to their 

 rejuvenation by faulting (see also Plate Xlla.), as well as to that 

 given by Chamberlin and Salisbury (ref. 10, p. 163) in their 

 diagram to represent the grades of a partly rejuvenated stream. 



The evidence presented, though not as complete as could be 

 wished, owing to the reasons stated, is yet sufficient to enable us to 

 map approximately the " Gisborne Fault/' — which here forms part 

 of the nortl^ern boundary of the great Port Phillip sunkland. The 

 fault has its greatest throw in the west, where the deeply-ravined 

 Ordovician of the upper Pyrete creek, etc., occurs; the throw 

 becomes much less as we proceed eastward. No date can be defi- 

 nitely stated, but the writer believes it to be probably of the same 

 age as the Greendale fault. 



(b) Fault bounding Southern edge of the Bnlkin Sunkland. 



(See Fig. 5.) The very important sunkland of Port Phillip, 

 and the less extensive but equally interesting one of Ballan, which 

 will be dealt with in detail later, have already been referred to. 

 These names are introduced at this point since it is felt to be the 

 most convenient method of referring to those particular areas. In 

 dealing with the southern edge of the Ballan sunkland, the writer 

 is again describing a feature which extends for some distance out 

 of his limited area. It has only been examined where it lies within 

 the Werribee basin, and other evidence to the west is based on pub- 

 lished geological maps and records. 



Physiograpliically we have no evidence of this fault, except that 

 the valleys immediately north of the fault, being in the much 

 younger and softer beds of the let-down rocks, are much wider 

 than those to the south. There is now no scarp present, as is indi- 

 cated in the north south section (Fig. 13); this figure also shows, 

 diagrammatically, the geology of the section. Spring Creek, a 

 tributary of the Parwan, flows for part of its course along the 

 boundary between the Ordovician and tertiary, i.e., along the fault 



