Plenty Biver and Anderson's Creek. 163 



The Probable Old Course of the Plenty. 



It has already been remarked that, in the writer's opinion, 

 the old course of the Plenty (now occupied by newer basalt) 

 was originally to the east of the Moranir Hills as far south as 

 Morang, and then probal)ly to the south-west, ^^^lat the actual 

 course was below Morang before the flow of the newer basalt 

 can only be surmised. The lava has covered such a wide stretch 

 of country to the west that the ridges and valleys have alike 

 been covered up. Tliat such ridges and valleys did exist is 

 proved by the remnants of the ridges and valleys to the north 

 and south of the main basaltic area. From the character of tlie 

 exposed ridges and valleys, the covered ridges were probal)ly 

 broad, and the valleys comparatively narrow. The southern 

 ends of the ridges, as at Preston and Essendon. are exposed, 

 apparently, on account of the basalt thinning out in its How 

 southward. Tlie uoi-tiiein outcrops, such as the Morang Hills 

 (granite and indurated silurian), some isolated hills at Donny- 

 brook (indurated silurian) and the hills at Broadmeadows 

 (mainly granite) may be accounted for by the hardness of the 

 rocks. They are probably residuals or monadnocks in the for- 

 mation of the peneplain, out of which tlie old pre-newer-basaltic 

 valleys have been carved. 



Assuming that the old Plenty came down the Moriing valley 

 its most probable lower course would be either to the west of 

 Preston down the old valley of the present Merri Creek, or down 

 the old valley of the present lower Darebin Creek. The latter 

 appears to be the more likely. If the Plenty ran soutli-wesrcrly 

 from Morang towards tlie Merri Creek valley, the old Darebin 

 Creek valley would necessarily be short, but so broad that it 

 would be out of proportion to its length. Moreover, the main 

 mass of the newer basalt is bounded by a ridge from Morang to 

 south of Bundoora. which suggests that such ridge formed the 

 continuous eastern boundary of an old stream. For these 

 reasons, the Darebin Creek valley is adopted as the original 

 course of the Plenty. It may be noticed that the valley is 

 narrow where the main road to Whittlesea crosses the Darebin 

 Creek ; but some very hard tertiary quartzites occur on the 



