Fhysioyraphy of Werribee Area. 



309 



be understood also that the terms '' older and newer volcanic " are 

 used here with the reservations mentioned in Section VIII. (a) of 

 this paper. More definitely, they may be taken as referring to the 

 two distinct periods of vulcanicity evident in the Greendale- 

 Bacchus Marsh area. The positions given to these two volcanic 

 periods in Fig. 39 must be taken merely as a general impression of 

 their relative ages. Subsequent decisions by geologists regarding 

 the exact positions of these events in the tertiary "time-line" 

 should not greatly affect the sequence recorded in this column. 



Fig. 40. — ^Generalised block diagram to show the chief structural fea- 

 tures of the Werribee River area. 



The great tertiary subsidences that are known to have taken place 

 in southern Victoria, with marine transgressions, should of course 

 be correlated with the diastruphic periods mentioned in this 

 column. While our marine series suggest three great ** breaks," 

 evidence of but two of these was found in the Werribee area. 



The sti-uctural features of the Werribee River basin, extremely 

 simplified, are shown diagrammatically in Fig. 40. This block 

 diagi-am is drawn as if viewed from thq east; it may be taken as a 

 summary of the writer's opinions of the main tectonic features of 

 the topography of the basin, minus the effects of the later lava 

 flows. 



The Newer Volcanic period, in later tertiaiy times, was accom- 

 panied by another great series of uplifts, associated in this area 

 with the Rowsley or Bacchus Marsh Fault. Since then the forces 

 of erosion, modified to sotne extent by every haj)pening that had 

 gone before, produced for us the hills and valleys of the Werribee 

 area as we know tbem to-dav. 



