160 J. T. Jatson: 



southern tongue about 100 feet above the same river. Where 

 the Maroondah Aqueduct crosses the present Plenty (which is 

 near the end of the narrow strip of basalt above mentioned) 

 the lower surface of the basalt is about 60 feet above the stream 

 and about 125 feet below the immediate top of the valley. (See 

 Fig. 2, which is a diagrammatic section at the Maroondah 

 Aqueduct.) From these measurements, and alloAving also for 

 the rise in the bed of the present Plenty, it can be seen that 

 there is a rapid fall in the lower surface of the basalt between 

 the northern tongue and the Maroondah Aqueduct. "Where the 

 valley rises above the level of the basalt flow, it is even now 

 fairly undeveloped, especially towards the end of the narrow 

 basaltic strip. It is clear, therefore, that the present Plenty 

 valley from Morang south-\vard existed before the flow of the 

 newer basalt, as a young valley Avith a rapid fall. Since the 

 lava stream, this valley has been re-excavated between the 

 basalt and the other rocks, but to a much greater depth, and 

 with an accentuation down to its mouth of its youthful 

 character. 



The conclusion is therefore reached that before the llow 

 of the newer basalt, there existed a broad, moderately mature 

 valley above Morang, and one indicative of youth below, 

 which reverses the normal order, if it be assumed that these 

 two valleys were then continuous. No satisfactory expla- 

 nation can be given for this unusual deviation. If, however, 

 the upper and lower valleys be regarded as originally distinct, 

 then the observed facts become explicable ; and the probable 

 sequence of events may thus be stated. Before the flow of the 

 newer basalt, the Plenty as n mature stream ran in a south- 

 westerly direction from Morang, ^ having as the eastern side of 

 its valley the more elevated land now forming the eastern border 

 of the main basalt flow, as before noted. The present lower* 

 Plenty formed an independent stream, young and vigorous, 

 with a steep grade and running in a south-easterly direction. 

 It had eaten its way back towards the old Plenty valley, near 

 Morang, and probably in time would have captured the head 

 waters of the stream there. 



1 If capture had taken plac-e at the Barber's Creek Gap the streams would be altered, 

 but the old valley at Moratiy reuiained. Such capture would not aflfect the present 

 ar'4uni(;nt. 



