Physiography of Werrihee Area. 233 



grading down to the lower basalt-covered Werribee plains (block 

 E). Towards the west there are two large areas of glacial con- 

 glomerate on the down-throw side, but otherAvise there are no 

 geological distinctions between the two sides of the suggested fault, 

 due largely to the extensive erosion and the covering of volcanic 

 material. 



Physiographically, we find this Gisborne block, whose elevation 

 is much increased by such volcanic masses as Mts. Bullengarook and 

 •Gisborne, is really on the average much lower than Block A — the 

 Blackwood and Lerderderg Ranges, and slopes downwards to the 

 east. The wide east-flowing valley of the Gisborne Creek occupies 

 the main part of the block, and this valley extends across to the 

 Main Divide at Macedon. There is, however, a fairly sudden 

 drop along a general east-west line, as may be noted when travelling 

 up the Bullengarook road, at the point where the basalt flow is very 

 narrow (see Fig. 22). The road from Coimadai to Toolern Vale 

 runs along parallel to and somewhat south of the line believed by 

 the waiter to mark this fault. To the north are higher, severely- 

 eroded, timbered ranges of folded lower Ordovician slates, quartz- 

 ites, etc., but the lower area traversed by the road shows abundant 

 gravelly deposits, some basalts, and a littl© permo-carboniferous, 

 while the Ordovician here outcrops mainly in the creek beds. 



On the main road from Gisborne to Melton we again find an 

 extremely steep fall of over 400 feet in little more than a mile 

 (Breakneck Hill). Further east, outside the area examined by the 

 writer, there is a steep climb for the train after it leaves Sunbury 

 for the north; this rise is mainly due to the erosive work done by 

 Jackson's Creek. 



The western part of the block, at the head of Pyrete and Djerri- 

 warrh Creeks, is a very deeply dissected mass of folded Ordovician 

 slates, etc. The exposures of these rocks become less extensive and 

 less rugged as we go east, and volcanic rocks become more and more 

 in evidence. To the south on the let-down block no Ordovician 

 occurs, except) at a very low level (about 600 feet) in the valleys of 

 the Pyrete and Djerriwarrh creeks, as may be seen where the Mel- 

 bourne road crosses those streams, or higher up near Coimadai. 

 Between the lower and the higher Ordovician a fall of over 400 

 feet is distinctly noticeable. This difference of level rapidly de- 

 creases to the eastward.- 



The most convincing physiographic evidence is found in the 

 grades of the rivers. The Pyrete, Djwerriwarrh and Toolern 

 screeks flow south from the Gisborne hi^^hlands into the Werribee. 



