Plenty River and Andersons Creek. 15^ 



above Morang. It formed an almost complete barrier to the east- 

 ward spread of the newer basalt. 



This barrier was penetrated between Morang and Janetield 

 by two narrow tongues of basalt from the main massr 

 as shown on Quarter Sheet 2 S.E. These tongues give the 

 key to the later history of the Plenty River. The accurate 

 mapping of the district by Apliu suggested to me, before 

 going over the ground, the solution of the problem. Both 

 these tongues have a slope south-easterly into a pre-exist- 

 ing valley; which now forms the lower Plenty valley. 

 From the main road to Whittlesea, at an elevation above sea 

 level of about 500 feet, the southern tongue descends rapidly 

 into the present valley. At its margin, close to the stream, 

 its upper surface is about 170 feet below the main road level. 

 This is not due to denudation, but represents with approximate 

 truth the fall of the basalt flow. Tlie softer silurian and ter- 

 tiary rocks on each side of this tongue slope from the main 

 road towards the Plenty at about the same angle as the basalt. 

 These rocks are even now mostly higher than the basalt tongue, 

 a fact which proves that the latter partly filled on old tributary 

 valley of the stream which is now the Plenty. 



The northern tongue shows similar features, but not so pro- 

 nouncedly as the other, and it has apparently been more denuded ; 

 but still it is clear that it ran south-easterly down a small valley. 

 (See Fig. 1, which is a diagrammatic section across the upper part 

 of this tongue in Section VI., Parish of Morang.) The southern 

 tongue iscontinued as a narrow strip not more than 30 feet in thick- 

 ness down the right bank of the present Plenty valley, and 

 getting deeper into such^ valley, until it ceases about a mile to 

 the north of Greensborough. It no doubt extended farther than 

 now mapped ; but was becoming thinner, and part has been 

 removed by denudation. Its upper surface is very even, and 

 it undoubtedly represents the approximately original surface of 

 the flow. This strip is now broken into sections by the short 

 but steep gullies joining the Plenty from the west. The 

 northern tongue Avas probably at one time continuous with the 

 southern one ; but river action has disconnected them. 



At the end of the northern tongue of basalt, the lower surface of 

 the latter is about 170 feet above the Plenty, and at the end of the 



