Physiography of Werribee Area. 289* 



to 500 feet. At Lara, towards the southern end of the plains, a bore 

 passed through 376 feet of gravels, limestones and clays of tertiary 

 origin. The general level nature of these volcanic plains, except 

 where interrupted by the very ancient residuals of the You Yangs 

 and Anakies, suggests that the underlying surface was also of very 

 low relief, while the evidence of the bores, etc., testify that this 

 surface was composed mainly of marine and estuarine materials 

 (tertiary). 



The writer visited the "basalt caves" south of the Parwan 

 railway station. These as far as explored were wholly in basalt,, 

 and were formed by the collapse of basalt blocks into some older 

 cavern. It may be that this older cavern was an " inter-basaltic 

 cave," formed by the flowing, away of the molten interior after the 

 outer parts had cooled; or it may be that, as at Mt. Mary, lime- 

 stones occur below, in which underground waters have dissolved out 

 a cavern, and into this some of the overlying basalt has subse- 

 quently collapsed. No positive evidence was to be seen in favour 

 of either hypothesis. This is the sum of our knowledge concerning 

 the buried river system of the Lower Werribee plains. This area 

 is therefore left out of our present considerations. 



The Blackwood Ranges have been shown to be but slightly 

 affected by the newer volcanic sheet, and that area, too, may be 

 largely left out for the present. We have to' consider, then, the 

 central -part of the area, containing the main plexus of this river 

 system, as it is drawn in Fig. 35. On this is set out all we have 

 learnt concerning the ages of the present day rivers and creeks, as 

 detailed in the preceding pages. It will be seen that the great 

 majority of the present streams are, without doubt, wholly post- 

 newer basaltic; their present valleys being cut through that rock. 

 These are shown by dotted lines. 



In a few cases it is doubtful whether or not the courses were 

 established prior to the newer basalts; such streams are put in 

 with dots and dashes, and thus they must be left until some evi- 

 dence is found. In yet a third series, the present river courses 

 are still almost the same as were established in pre-newer basaltic 

 times, and are marked with an unbroken line of arrows. These 

 lafit-mentioned streams indicate something of the trend of the old 

 drainage system; the Lerderderg strongly suggests that the main 

 slope here lay south-easterly. 



Our work lies now in those areas where newer volcanic rocks at 

 present occur. In endeavouring to find out the secrets of the rivers 



