[Proc. Roy. Soc. Victoria, 31 (N.S.), Part I., 1918]. 



Art. VIJ. — The Significance of Lava Residuals in the Develop- 

 onent of the Western Port and Port Phillip Drainage 

 Systems. 



By ROBERT A. KEBLE 



(Field Assistant, Geological Survey of Victoria). 



(With 10 illustrations in the text) 



[Eead June 13th, 1918]. 



This paper is the outcome of several years of observation in the 

 drainage systems of Western Port and Port Philip. As it affords 

 the most typical instances of that topographical form — the lava 

 residual, the development of which is the subject of the paper — 

 the Western Port area, where it is a conspicuous feature, has 

 perhaps received more attention. The Yarra has been navigated 

 from above Launching Place to its mouth, a journey of over a 

 hundred miles, and there is perhaps no better way of demonstrat- 

 ing the truth of the axioms of physiography than to experience 

 their effect. From Launching Place to the W^arrandyte Gorge, the 

 Yarra, except at a small gorge just below the confluence of the 

 Watts and the Yering Gorge, meanders over a flood plain, and is 

 comparatively sluggish. 



The Beaconsfield, Berwick, Pakenham, Gembrook, Woori Yal- 

 lock, Nar-nar-goon, Tynong and Drouin districts, afford the most 

 suggestive physiography; generally the Western Port area seems to 

 furnish the key to much that is inexplicable in the Port Phillip 

 area. 



In treating with such an extensive area, I have been prompted on 

 the one hand by the inseparable relationship of the one system to- 

 the other, and on the other hand, by the desire of fornmlating a 

 general scheme of classification before attempting more detailed 

 observations on smaller areas. 



/. — Introductory. 



Ihe residual and its physiographical significance. 



Previous work. 



Bass Strait lava field. 



Pre Older Basalt cycle of Western Port and Port Phillip systems. 



Western Port and Port Phillip lava fields. 



10 



