166 ./. T. Jithon : 



stream, the wide mouth of the Plenty valley and the extension 

 of the alluvium up that valley, are partly explained by the 

 diversion of the Plenty waters from above Morang. 



From these circumstances it may be inferred that the Yarra 

 valley was. at the time of the newer basalt liow. as far as its 

 junction with the old Plenty valley (the Darebin Creek valley) 

 similar to that now above Templestowe. and hence a young 

 valley. Tlie old Plenty! .^^^^ ^\^q q\^ Merri Creek were, judged 

 by their valleys, ajDparently more developed than the Yarra. 

 The latter stream probably joined the old Plenty near Fairfield, 

 which in turn would join the old Merri Creek at Clifton Hill. 

 The combined streams would then flow down the valley of Col- 

 lingwood and Piichmond (now occupied by the newer basalt) to 

 Melbourne. At this time the Yarra could not, perhaps, from 

 its stage of development, be regarded as the main stream. 

 With the diversion of the upper Plenty waters, however, con- 

 sequent on the eruptions of the newer basalt, the old Plenty 

 valley received only the small Darebin Creek ; but even this 

 was turned into the Yarra above the l^asalt. The Yarra also 

 received the whole of the water from the present Plenty basin. 

 It thus gained increased erosi^'e power, which enabled it to cut 

 its channel below Fairfield much faster than its only rival, the 

 present Merri Creek (the drainage area of which, since the flow 

 of the newer basalt, is much less than formerly, if, as sug- 

 gested above, the old Moonee Ponds Creek once joined it) ; and 

 so the Yarra became the predominant stream. 



Summary. 



The IMeuty Ptiver originally passed down the Morang valley, 

 and from Morang prol)al)ly ran south-westerly and southerly 

 into what is now the Darebin Creek valley. This old Plenty 

 valley was fairly well developed before the newer basalt flow. 



Tlie possibility of changes in the course of this stream before 

 the eruption of the newer basalt is indicated. 



The present Plenty Ijelow Morang was originally an indepen- 

 dent young stream, with its heads near Morang. and with a 

 steeper fall than at present. 



1 The stream ix'fen-ed to here and showii as an old river on Mk' iicoompanvin!,' man i** 

 what is mentioned above as the nrij;inal Plenty. It rapture had taken place at the 

 Barber's Creek (Jap, of course the remaining stream down the lower jiart of thv ori-^inal 

 rienty valley wouhl l)e much reduced. 



