Plenty River and Andersons Creek, 157 



near South Yan Yean. Looking from the elevated ridge which 

 forms the eastern side of this valley, at a point about a mile 

 south of Doreen, and just to the east of the road running from 

 Doreen to the main Diamond Creek Road, a great low-lying 

 valley, whose western side is over three miles away, is seen. 

 Newer basalt (through which the present Plenty is cutting) 

 occupies the floor of this valley, and has passed up some of the 

 eastern tributaries. 



It is evident, therefore, that the valley existing when the newer 

 basalt was erupted was a wide, well-matured one. Lower down, near 

 Morang, this old valley narrows, but still is moderately developed, 

 as the distance from crest to crest of the bounding ridges (probably 

 just under 2 miles) shows. These ridges are higher than their con- 

 tinuation northward, and this is perhapsdue to the rocks to the north 

 being softer and having suffered more denudation. The western 

 ridgeat Morang consists of granite^ intrusive into the silurian, which 

 has been hardened and indurated. The hardness of the rocks 

 forming the eastern ridge is not so obvious ; but many sections 

 in the Plenty show thick beds of sandstone, which evidently has 

 considerable resisting power here. The height of the western 

 ridge at Morang is also explained — as noticed below — by the 

 probability that its top formed a monadnock on the peneplain, 

 out of which the old valley was carved. South of Morang, the 

 old valley apparently ran to the south-west. This old valley 

 appears to have been that of the original Plenty (i.e., the stream 

 formed on the uplift of the peneplain) ; but whether, in view 

 of Mr. Hart's suggestion, it remained so until the eruption of 

 the newer basalt, is not certain. 



The determination of this point is not, however, material, for 

 the main purpose of this paper ; but it might be observed 

 in passing that the gap in the western ridge near Yan Yean, 

 where Barbers Creek now enters (which is the point where the 

 old Plenty would turn to the west if captured by a tributary 

 of the old Merri Creek) could be made by a tributary of the old 

 Plenty, just as well as by the backward (eastward) erosion of 

 this old tributary of the Merri Creek. This gap has a parallel 

 on the eastern side of the Plenty, where the tributary streams, 



1 The term "granite" (which is that used on the maps of the district by the old 

 Geolos'ical Siirvey of Victoria) is here used as a broad field-name only. 



