Plenty River <md Anderson-'^ Creek. 167 



The newer basalt obliterated most of the old Plenty, and 

 overflowed the heads of the independent valley by two small 

 tongues of basalt. By means of these tongues, the upper Plenty 

 waters were diverted to the south-east into the independent 

 valley, which has since been more deeply cut into. The old 

 valley above Morang has been deeply re-excavated. 



The newer basalt covered some of the ridges as well as the 

 valleys, and so largely obliterated traces of the old streams ; 

 but despite this, the basalt flows are invaluable for tracking 

 these earlier streams. 



The striking difference in the power of resistance to erosion 

 between the newer basalt and the silurian sediments, is indicated 

 by a comparison of the grades of the present Plenty above and 

 below the point where the stream has cut through the basalt 

 into the silurian. 



The effect on hard rocks is also shown at Morang, where, 

 through the delay in cutting through such rocks, the old stream 

 formed a wide open valley above. 



The tops of the Morang Hills and of other high points are 

 suggested as monadnocks on the peneplain out of which the 

 Plenty was originally carved. 



The diversion of the upper Plenty waters at Morang in con- 

 sequence of the newer basalt flow, has accentuated the lateral 

 erosion of the Yarra between Fairfield and Templestowe. 



The Yarra was probably less developed prior to the newer 

 basalt eruptions than the old Plenty River and Merri Creek, 

 and perhaps, judged from that standpoint, could not be regarded 

 as the main stream ; but since then it has become the pre- 

 dominant river. 



ANDERSON'S CREEK, WARRAXDYTE. 



From almost any of the higher view-points at Warrandyte, 

 the tops of the hills and ridges can be seen stretching away in 

 so even a line that there can be no doubt that they are the 

 remnants of an old peneplain, the highest points of which (in 

 the immediate neighbourhood of Warrandyte) are probably 

 about 450 feet^ above sea-level. This peneplain has, since its 



1 All the heights ineiitioued in this part of the paper are based on aneroid readings. 



6a 



