Physiography of Werrihee Area. 205 



(iii.) Age of the Uplift .— From a consideration of the above ex- 

 tracts and their accompanying reports, it seems justifiable to 

 assume that the penephmation was general over the whole continent, 

 •and that uplift of the peneplaned area to form the present high- 

 lands of Australia may possibly liave taken place at very nearly the 

 ^same geological period. It is generally agreed that tliis uplift dates 

 somewhere between middle tertiary (miocene) and pleistocene times. 

 The stratigraphical evidence on Avhich the date of the completion of 

 *the peneplain is based mainly exists in Victoria. Therefore, having 

 taken a brief survey of the extent of the general peneplanation and 

 R.iplift we shall return to the problem of the date as far as it may 

 be discovered in this south-eastern corner of Australia. 



It is of course understood that we may have peneplains of various 

 :stages of completion yet each deserving of the title of peneplain. 

 A very long period of still-stand of the land must be necessary in 

 •order to accomplish the perfect base-levelling of an area, but we 

 ^appear to have had in Victoria a surface which closely approxi- 

 mated to that ideal. Immediately any uplift took place on the 

 peneplain, rejuvenation of the streams would result, with dissec- 

 tion of the peneplain surface. The date of the commencement of up- 

 lift therefore marks the completion (or cessation) of the particular 

 (Cycle of erosion which formed the peneplain. 



The rocks which formed the surface of the peneplain in Victoria 

 ^vere for the greater part the low^er and upper Ordovician, and the 

 Silurian rocks — all of which may be regarded as one rock type as 

 far as erosion is concerned (see description of rocks, supra). The 

 schists and gneisses of N.E. Victoria and the intruding granite 

 masses also form.ed portion of the planed area, as did the softer 

 level-bedded sandstones of the glacial period (Bacchus Marsh, 

 Heathcote, etc.), the carboniferous sandstones and mudstones 

 •(Grampians, Mansfield, Mt. Wellington, etc.), and the devonian 

 <Tabberabbera, Buclian, etc.) shales and limestones. Each of the 

 tliree last named series of rocks now exists in limited areas only; 

 they are mainly of a much lower order of resistance than the beds 

 first mentioned, and are probably now largely preserved in patches 

 Avliere they may have occupied valleys and fault-troughs at the time 

 of ])lanation. In 1866, Selwyn (ref. 50) put forward the idea that 

 tlie Mansfield-Grampians series of sandstones had once extended 

 1 i<ilit over that surface of Victoria tliat now separates the two main 

 occurrences. (See Section Vila.) The numerous and scattered 

 relics of our jjlacial sandstones .susfgesfc that they were for- 

 merly enormously greater in extent; there is no doubt they liave 



