PhysiograpJiy of Yarra, etc. 483 



This axis may be a true erustal deformation formed during 

 the differential uplift of the Nillunibik Peneplain. Whether 

 it is so or not as regards the northern and southern slopes, 

 there seems to be no doubt that its gradually increasing eleva- 

 tion eastAvard is due to earth movement. At Burt's Hill the 

 rocks snapped, forming the Brushy Creek Fault. 



Tlie axis, if wholly due to erustal movements, really forms 

 iin elongated dome, truncated at its eastern side. 



The general uplift of a wide area of country had given a 

 .southerly slope to the Yarra Plateau from the foot of the Main 

 Divide, and this slope met the northern slope from the 

 Mitcham Axis somewhere about the course of the present Yarra 

 (west of Brushy Creek). The axis therefore determined to 

 some extent at any rate the course of the Yarra, and fixed the 

 boundary line between the basin of that river and that of the 

 Dandenong Creek. 



At Mitcham and eastward to Burts Hill at Croydon, the 

 northern and southern slopes can be clearly seen from the 

 axis. Farther west however the slopes are less in grade, and 

 therefore not so distinct. About Box Hill the axis is a broad 

 level stretch of country, in which streams have in their head 

 waters incised themselves in a westerly direction. These 

 streams, however, in their lower courses tlow, as a rule, to the 

 north or the south. 



The evidence as to the warping of the country along the 

 Mitcham Axis is not based on the structure of the underlying 

 rocks. No definite results can be obtained from them. It is 

 based on the slopes of the ridges to the north and south of 

 the axis, particularly at Mitcham and Burt's Hill, on the 

 gradual rise of the axis from west to east, and on the slope 

 of the country west of Bayswater being towards the east, whilst 

 some of the streams run westerly, as will be subsequently 

 noted. 



The amount of fall along the ridges has not been deter- 

 mined ; but those extending from the Mitcham Axis northward 

 to the Yarra appear to have a gentle slope until the Yarra is 

 approached, when they dip sharply towards the river, the sharp 

 dip being clearly due to denudation. It is ditficult however to 

 see how denudation since uplift could have produced the main 



17a 



