Physiography of Werribee Area. 231 



glacials lies at 660 feet in, the Werribee Gorge, and at 1400 feet in 

 the Lerderderg area (about 5-6 miles N.-N.E.). This anomaly is 

 explained by the intervening fault. 



The fault after crossing the Korkuperrimul, forms the northern 

 boundary of the big let-down glacial block east of that river. For 

 a few miles here, the writer is assuming the fault on the basis of 

 previous geological and contour surveys, where the evidence is 

 analogous to that of areas where the line was closely examined. 

 Observations from viewpoints to the east and west confirm the 

 assumption that the fault thence continues past Mr. Robertson's 

 house, "Highlands." Here Robertson's Creek has followed the 

 fault for some distance, providing excellent and unmistakable 

 exposures. As we pass down this creek, we find always on the left 

 the high block of Ordovician which forms the south-eastern trian- 

 gular termination of tlie Lerderderg Ranges, (Fig. 6a.) To the 

 south-west we invariably get younger beds, let down, and tilted at 

 varying angles towards the south and south-east; these consist of 

 the Bacchus Marsh tertiaries, thick flows of older volcanic, glacial 

 sandstones and conglomerates, and also what appeared to be sub- 

 glacial river gravels; all these deposits show signs of disturbance. 

 The Greendale scarp then meets the Rowsley or Bacchus Marsh 

 scarp. The consequence of this is of course that the northern con- 

 tinuation of the Rowsley fault has a much greater throw than fur- 

 ther to the south. 



Physiographically, in addition to the abrupt change of elevation 

 mentioned and shown in diagrams, we have various features in the 

 rivers which point to the truth of the explanation of the Greendale 

 scarp as being due to a moderately rapid uplift of the noi-thern 

 block; it was considered more convenient to deal with such featui-es 

 when describing the rivers. .As already detailed, conclusive fault 

 evidence occurs abundantly in the field, much more telling than 

 diagrams and descriptions. Still, the evidence so far put forward 

 in this paper is sufficient to show positively that the scarp described 

 marks a line of extensive faulting. In consideration of the fact 

 that it was first definitely proved near the village of Greendale, it 

 is called the " Greendale fault." For plan see b, Pig. 5. 



To come now to the question of age, we find that, while in some 

 cases the face of the scarp is remarkably well preserved, there is 

 other physiographic evidence (such as the greatly dissected nature 

 of the alluvial apron) which suggests that this scarp is much older 

 than that of the Rowsley Fault. 



17a 



