154 J. T. J at 



son : 



which it has cut its way. After traversing this formation for 

 about two miles, it finds its way to the junction of the basalt 

 and the silurian, but breaks away into the latter in two places, 

 and also cuts through the basalt a similar number of times. 

 Apart from these deviations, however, it keeps to the junction 

 mentioned to Morang ; then is bounded in different parts by 

 older and newer basalt, and tertiary and silurian sediments 

 (the silurian predominating), until it reaches the Yarra. From 

 the time the river enters the newer basalt until it finds the 

 junction with the silurian, its valley in the basalt does not 

 become more than about 30 feet deep ; but when it reaches 

 the sedimentary rocks, it soon becomes a winding gorge, 

 whose deepest part is near Morang, where it obtains a depth 

 of close upon 250 feet from the surface of the newer basalt 

 plain. The latter is lower than the opposite or eastern ridge 

 of older rocks ; so that from this side the depth would be 

 greater. Here the valley is markedly V-shaped in cross sec- 

 tion and is of rugged beauty. Its sides are steep and densely 

 clothed with timber, and the newer basalt outcrops in large 

 boulders, mainly on the right bank, at the top of the valley ; 

 while some splendid silurian sections are displayed on each 

 side. In cross profile, the spurs show the steep short cliff of the 

 basalt, and the longer, more gentle slope of the silurian beneath. 

 After the newer basalt is left behind, the outlines of the valley 

 become softened, as at Greensborough, but the youthful character 

 of the stream is most obvious. A noticeable feature is the 

 absence, south of Morang, of all but the most insignificant tribu- 

 taries. At South Yan Yean and Morang, the newer basalt 

 partly fills a large old valley, which is comparatively contracted 

 at Morang, with high bounding ridges, but is wide and open 

 at South Yan Yean, with lower ridges forming its sides. 



Previous Literature and Remarks Thereon. 



The only previous references to the physical history of the 

 Plenty valley appear to be by Mr. T. S. Hart, M.A., and Prof. 

 Gregory. Mr. Hart, in his interesting and suggestive paper, 

 "The Volcanic Rocks of the Melbourne District," i referrin<r to 



1 Victorian Naturalist (1894), vol. xi., pp. 74-78. 



