Physiography of Werribee Area. 197 



to (see Fig. 4). Excejit the smaller outlier of the Cathedral Range, 

 in the Acheron Valley, no tracts of these upper palaeozoic rocks 

 have vet been recognised between the Grampians and the Mansfield 

 ai'ea. Possibly, therefore, tliis intervening area Avas in those times 



Fig. 4 — Section to illustrate Selwyn's conception of the possible o-eologieal 

 strncture of Victoria as referred to in Section Vila. This shows a 

 geosyncline of Lower Palaeozoic rocks, with a broken anticlinal arch 

 of Upper Palaeozoics. The underlying schists and gneisses have 

 been added to those shown in Selwyn's diagram. 



an elevated north-south area on the flanks of which these two 

 widely-separated deposits may have been laid down in two distinct 

 basins. Tlie possibility that they once extended across the area 

 under discussion is, however, worthy of consideiation. 



In the pei-mo-carboniferous period vast sheets of glacial material 

 were deposited on the Ordovician, and many remnants still remain; 

 the protective effect of these beds must be borne in. mind, but the 

 glacial period itself is, in the foregoing paragraphs, regarded as 

 an erosive period as far as the lower palaeozoic rocks are concerned, 

 There does not appear to be any good reason for believing that the 

 Jurassic sediments of southern and south-western Victorian ever 

 extended so far north as to affect the Werribee River area. Neither 

 does it seem probable that the tertiary marine invasions ever 

 extended over tlie present Ordovician uplands of the area dealt with 

 in this paper. 



Induration of tliese lower .Ordovician rocks is in all cases so 

 advanced that although, owing to the repeated folding, a variety 

 of beds are exjjosed running in N.S. lines, little differential erosion 

 is to be noted. In some cases in Block Ai (the Blackwood Ranges), 

 north of Greendale wide quartzite bands may be followed along 

 the ridges, in the formation of which they have no doubt played 

 their part. Both E.W. and N.S. dykes occur; in places the former 

 are very numerous. 



Considerable faulting and jointing is noticeable and this has 

 helped to give direction to various valleys. An interesting case is 

 that .()f Back Creek, surveyed by the Melbourne University Survey 

 Party in 1915. As shown in Fig 3-3, this stream is a fairly good 

 example of a " drainage network " (ref. 32, ]>. 226). In places 



15 



