148 Robert A. Kehle: 



comes wider and wider as the captured head-waters more rapidly 

 upproach maturity, and' the severed portions of the residual be- 

 come more isolated. 



The important part played by breaching, and the subsequent 

 development of the cross streams, is shown in a typical way by the- 

 development of the Yarra (Fig. 5). The movement originally re- 

 sponsible for the breaching of the Melbourne residual in the 

 vicinity of Melbourne occurred along a fault line parallel with the 

 east side of Port Phillip Bay. Along this line of weakness at a 

 later date the fault block of the Bay itself moved. The eastern, 

 lateral of the residual Avas diverted through the breach, and the 

 subse(iuent rejuvenation extended along it and all its tributaries.. 

 A tributary of the eastern lateral was the Plenty River of the- 

 period, and an important tiibutary of the Plenty River was Dia- 

 mond Creek, the western lateral of the Kangaroo Ground residual. 

 The eastern lateral of that residual, viz., Watson's Creek, was 

 diverted through a breach into Diamond Creek and rejuvenated.. 

 Subsequently the Wurunjerri Range was breached by a tributary 

 of Watson's Creek, and the basin of the Middle Yarra diverted 

 through the breach. The middle Yarra, previous to its diversion,, 

 found an outlet to the south of Lilydale either through the Lyster- 

 field Gap or Dandenong. The immediate effect of the diversion 

 was to reverse the direction of part of this southerly trending 

 stream, so that we now have the western lateral of the Lilydale 

 residual (Brushy Creek) flowing northwards, not southwards. 



The breaching of the Lilydale residual and the subsequent cap- 

 ture and rejuvenation of the head-waters of the eastern lateral 

 have been referred to (p. 147 ante). Belonging to an earlier period 

 than the series of breachings and rejuvenations, just described 

 in the development of the Lower Yarra, is the system of breaching 

 and rejuvenation in the basin of the Middle Yarra. The eastern 

 lateral of the Lilydale residual, rejuvenated, was powerful enough 

 to breach the Woori Yallock residual, which resulted in the diver- 

 sion of the Watts and the Woori Yallock River, which for a short 

 time at the inception of the Intermediate cycle, had a southerly 

 trend. The rejuvenation resulting from the breaching of ?the 

 Woori Yallock residual probably accomplished the breach at War- 

 burton, which resulted in the diversion of portions of the laterals 

 of the infilled valley from the vicinity of Mt. Buller to Flinders. 



From the fact that it is a series of laterals and breaches the 

 Yarra has a circuitous trend, but the breaches give its valley a 

 dominant gradient to the west. The Yarra and the upper portioii 



