30 RIVER YARRA, VICTORIA 
of which are seen along the Mitcham Axis. Modifications in the 
definition of the Yarra Plateau require modifications in the 
definition of the Nillumbik Peneplain. I suggest that this name 
be used for the peneplain standing from 400 ft. to 450 ft. above 
present sea-level. The map (Fig. 3) and sections (Fig. 4, a-c) 
show the extent of this peneplain. In addition to the Mitcham 
Axis there is a ridge running north-west to Doncaster, and another 
running south-west to Tally Ho and Mt. Waverley (cf. Hart, 
1913). 
Very important is the fact that the peneplain caused a gap in 
the Wurunjerri Range. Fig. 3 shows a stretch of about three 
miles of the Brushy Creek escarpment south of the Yarra River 
with summits at the Nillumbik Peneplain level. The east side 
of the Yering Gorge (Fig. 4b; also Gill, 1942, fig. 3) and the hills 
to the north of Lilydale are likewise Nillumbik levels. Most 
significant of all is the fact that the Older Basalt residuals at 
Lilydale and north-west of Lilydale stand on the Nillumbik 
terrain. This means 
(a) that the Nillumbik Peneplain stretched across to the Dan- 
denong Mountains; 
(b) that this area was not down-faulted in post-Nillumbik times 
as claimed by Jutson (1911); 
(e) that the Lilydale Older Basalt is not a pre-Nillumbik pene- 
plain lava flow, but one extruded after the formation of the 
peneplain. 
Standing out from the Nillumbik Peneplain was a monadnock 
(or, if the plain were covered by sea, an island) which constituted 
the southern end of the Wurunjerri Range. This geographic 
feature owed its presence to the rocks of which it was composed— 
the Western Quartzites. As in the high country north of the 
Yarra, the elevated features are due to an anticline in the Western 
Quartzites. 
On the other hand, the breach in the Western Quartzites where 
the Yarra passes through is due to 
(a) lateral differentiation of the country rock; 
(b) structural disturbance. 
(a) Although there are no soft strata, the rocks in general are 
not so quartzitie as those, for example, on the Lilydale Highway 
where it descends the Brushy Creek escarpment. 
(b) In the vicinity of Warrandyte, the Warrandyte Anticline 
divides into a number of small folds and then pitches out of 
existence. On the Wonga Park Road there are northerly dips for 
