Zo W. R. BROWNE. 
gorge (see Plate IV, fig. 4), and in the fact that we find 
youthful streams flowing in old valleys, as in the case of 
Pilot Creek. There is no stratigraphical evidence of the 
fault, but the fact that we do get the same schists and 
gneisses on the low ground to the west of the scarp as 
occur on the higher ground to the east, would go to show 
that the scarp is due to something else than differential 
erosion. 
On the basis of Stissmilch’s conclusions I have tried to 
work out in some little detail the physiographic history of 
the area with which I am concerned. 
The ancient valley of the Upper Murrumbidgee, from the 
point where near McCarty’s Crossing it now turns abruptly 
east, can be traced south till it joins the broad old valley 
of Slack’s Creek. The ancient course of the river is now 
blocked by thick basalt flows, and bounded by ridges of 
phyllite and quartzite, and its contours are in marked con- 
trast to those of the present Upper Murrumbidgee. The 
latter has been rejuvenated in consequence of the uplift, 
and has cut down a comparatively recent gorge through its 
former mature bed. The old valley forms the diagonal of 
a quadrilateral formed by Bridle Creek and Slack’s Creek 
on the west and east, and the Murrumbidgee and the 
Adaminaby road on the north and south respectively. The 
old river joined Slack’s Creek or its south-flowing ancestor 
just south of the Adaminaby road, and thereafter flowed 
to the S.W., crossing the site of the present divide just a 
little to the west of the Dalgety road. The valley now 
known as Dairyman’s Plain was probably a tributary. 
With regard to the other part of the Murrumbidgee, north 
of Mittagang, there is less certainty. At the time of the 
uplift the country was in a state of very mature erosion; 
the dividing ridges between the broad meridional valleys 
had been considerably worn down and there was doubtless 
