Physiography of Werribee Area. 



247 



While we see that over an area of low relief the basalt spread 

 ;as a great level sheet, filling the valleys and covering the low 

 "dividing ridges, this was not the case in the higher country where 

 •deeper valleys existed. In at least live places we have the volcanoes 

 originating in higher areasi, and sending their lava flows as long 

 tongues down the existing valleys. 



In some cases this infilling resistant tongue caused the forma- 

 tion of two new streams, one on either side of the basalt flow. Such 

 streams run closely parallel for good distances, and are very com- 

 mon in many parts of Victoria — e.g., Goodman's and Pyrete 

 <;reeks, upper parts of Myrniong and Korkuperrimul creeks, etc., 

 ■etc. It is so characteristic a feature that for the purposes of our 



Fig. 16. — Diagrams to illustrate the origin and progressive erosion 

 of " Twin Streams." In connection with the Newer Basalt flows 

 in Victoria, such erosion has rarely advanced beyond the stage 

 shown in D. 



local geography, it might be well if a special name were used for 

 descriptive purposes. On account of the similarity of their nature, 

 and the contemporaneity of their origin, it is suggested they be 

 .called " twin streams" (see Fig. 16a, b, c. d). 

 The basaltic tongues referred to are : — 



i. From Leonard's Hill and other points thereabouts, long 

 tongues came southward down the valley of the upper 

 Werribee, through Korweinguboora, etc. (It is pos- 

 sible that some ** older l)asalts " occur here also.) 



