512 J. T. Jut son: 



Summary. 



The Nilluinbik Peneplain, consisting of an elevated area — 

 the Yarra Plateau — and a depressed area — the Croydon Sen- 

 kungsfeld — is described and its age discussed. 



The Croydon Senkungsfeld is shown to be a fault-block, 

 bounded mainly by faults and their scarps. The faults traced 

 are the Brushy Creek Fault, the Yarra Fault, and a probable 

 fault named the Dandenong Fault. The latter has a length 

 of nearly fifty miles, whilst the Brushy Creek Fault is traceable 

 by its scarp for about eight miles, and the Y^arra Fault simi- 

 larly for about nine miles. 



The uplift of the Nillumbik Peneplain was both slow and 

 differential. It was so gradual that the Y^arra was able to cut 

 deep gorges — the Y'ering and Warrandyte Gorges — as fast as 

 the land rose. The differential movement accounts for the 

 Croydon iSenkungsfeld, which is a relative and not an abso- 

 lute depression. 



The Y^arra and Dandenong Creek Basins are divided by a 

 line of elevated country — the Mitcham Axis — which is in part 

 at least due to crustal movement. 



The Yarra River is in a certain portion clearly antecedent 

 to the present topography, and in its course through the 

 Yering Gorge and part of the long Warrandyte Gorge is a revived 

 stream. 



The Yarra Flats and low adjacent country are primarily due 

 to being part of the Croydon Senkungsfeld, through which ver- 

 tical erosion almost ceased while the Y^ering and Warrandyte 

 Gorges were being excavated, but lateral erosion was active. 



The Yering Gotge is an isolated gorge of the Yarra, and is 

 extremely valuable for the light it throws on the physiography 

 of the whole district. 



The Dandenong Creek and its principal tributaries are 

 antecedent and revived streams. 



The Bayswater and Scoresby Flats are within the Croydon 

 Senkungsfeld, and l^elong to the Dandenong Creek Basin. Their 

 origin is due to causes acting similarly to those which have 

 caused the Yarra Flats.' 



