Physiography of Werribee Area. 



285 





Fig. 34. — Plan of an interesting, though minor, physiographic feature 

 on the Myrniong Creek, where a bar of basalt, filling an old 

 stream valley, crosses the present stream course. Outside the 

 basalt, the rock is granodiorite. Below this bar the grade of 

 the Myrniong steepens rapidly. 



more direct for the Myrniong to have continued straight on to the 

 Werribee without cutting through the obstructing basalt. There are 

 two possible answers to the question. Firstly, the basalt sheet may 

 then have been much more extensive, and the Myrniong, flowing 

 on that sheet, might have been pledged to its present course before 

 at had cut down and ** discovered " the present obstruction. Or, 

 secondly, and more probably, the Myrniong really did once, in its 

 early days, flow direct into the Werribee at the place mentioned, 

 and was captured by the headward erosion of a small stream, 

 which may have entered the Werribee below the resistant basalt 

 bar that once crossed the latter stream near the eastern end of " the 

 Island." After crossing this bar, the Myrniong runs eastward, 

 looping round ** the Island," and entering the Werribee. For 

 this part of its course the valley is very young and steep-sided, 

 with a grade of over 400 feet to the mile. The effect of the oh- 



