Physiography of Werribee Area 



2Gi) 



extreme head waters grade rapidly up to the basalt plains. This is 

 due to the fact that the course of the ParAvan above the scarp is in 

 extremely soft, level-bedded, tertiary sands, etc., with a thin 

 basalt covering, while the Werribee was in hard, folded Ordo- 

 vician, etc., also partly covered by a basaltic sheet. (See Fig. 24.) 



.600 — 



1200 — 



400 — 



600— Il-_— 





4 {\AikS 



1200 



^Basalt 



^'■^'^ Werribee 



2 Miles 



Fig. 24. — Sections across the valleys of the Parwan and Werribee 

 valleys, at approximately equal distances above the scarp. To 

 show the extent of the work of the Parwan in soft, level-bedded 

 Tertiary sands and clays, compared to that done during the same 

 period by the Werribee in the more resistant Ordovician, granite, 

 and Pernio- Carboniferous rocks. 



It will be noted that Pyke's Creek, while it flows for a couple of 

 miles at levels higher than those of the parallel Werribee, rapidly 

 deepens, and for nearly four miles is much lower than the latter, 

 entering at a gentler grade than that of the parent stream. The 

 explanation is probably to \ye found in the fact that Pyke's Creek, 

 with its many tributaries, has a larger catchment area than has 

 the Werribee from their junction upwards. Pyke's Creek basin 

 also lies for a good part of its course in more easily-eroded rocks — 

 sandstones, decomposed older volcanics, and tuffs. It is no doubt 



