Physiography of Werrihee Area. 235 



line. Where investigated by the writer, this valley is steep and 

 V-shaped, over 300 feet deep; on the right bank the high resistant 

 slates, etc., of the Brisbane Ranges occur, truncated at right angles 

 to their strike, while in the bed of the creek and high on the left 

 bank, easily eroded tertiary beds ('Meaf-beds ") occur. These are 

 capped by newer volcanic, which further west extends well over the 

 fault line towards the south. Two streams — a southern tributary 

 of Yaloak creek (flowing north), and the eastern Moorabool (flow- 

 ing south) — cross the fault line, and might be expected to provide 

 good sections. This is found to be the case, since the geological 

 map of the parishes of Bungeeltap, etc., by Mr. E. J. Dunn (re- 

 cently published) shows valuable confirmatory geological evidence of 

 the fault. 



In the Eastern Moorabool the steep valley sides change abruptly 

 from the hard Ordovician to the soft tertiary sand and clay beds. 

 The Yaloak creek tributary shows just as sudden a cutting off of 

 these two formations, giving rise to the peculiar tributary, like an 

 inverted T, shown in Fig. 37. Both junctions referred to are in an 

 almost straight east-west line, and are also in line with the area on 

 Spring creek, where the fault was first assumed by the writer. Mr. 

 Dunn's map was kindly brought under my notice by Mr.. 

 Baragwanath. The writer has mentioned this evidence to Mr. T. 

 S. Hart, and he suggests the same fault may continue to the west 

 and form the southern wall of the very deep basin of the Lai Lai 

 brown coal beds (ref. 24). The pre-existence of this fault junction 

 may have influenced the Rowsley fault, causing it to change direc- 

 tion slightly at the point of intersection. 



This fault, which may be called the Spring Creek Fault, is there- 

 fore put forward as the explanation of the very significant struc- 

 tural line separating the barren and unproductive Brisbane Ranges 

 from the rich and geologically varied area of the Ballan sunkland 

 to the north. It is perhaps of the same age as the Greendale 

 fault, runs nearly east-west, and has a considerable down-throw to 

 the north. 



(c.) The Sfeiglitz Fault.— llQXitiow of the Steiglitz fault is in- 

 cluded here, in order to have as complete a record as possible of the 

 chief faults within this area. The writer has, unfortunately, been 

 unable to follow this line; he has, however, examined the country 

 to the northward, at Steiglitz, both geologically and physio- 

 graphically, as he has also done to the south, in the Maude and 

 Lethbridge areas. 



