j208 Chart fs Fenner .- 



whether they are coirectlv referred to the '^ Older Basalt," and if 

 so, as to whether they are contemporaneous, or part of a series of 

 <:;ruptions extending over a long period of time." 



The correlation of the ages of the Victorian basalts with those of 

 New South Wales and Queensland seems to be even more a matter 

 •of conjecture. The main argument apparently is that where the 

 general relations seem to point to basaltic lavas belonging to an 

 older tertiary period, a correlation in age with the older basalts 

 of Victoria is assumed, the- grounds for such assumption being 

 that since Eastern Australia appears to be a fairly compact tectonic 

 unit, it is likely that the volcanic periods of the different States 

 Avould be, in general, closely related in time. 



It is unfortunate that much of the past physiographic work done 

 in New South AVales has as far as time is concerned, been based 

 on the assumption that the ages of the Victorian basalts and ter- 

 tiaries were generally agreed on. The matter recurs in other parts 

 of this paper, and is there discussed from the other points of view. 



Having noted the above deficiencies in our knowledge of the ages 

 of Victorian tertiary rocks, the writer feels the necessity for defin- 

 ing his beliefs in the matter. After a careful consideration of the 

 •evidence, therefore, it is here assumed, with the cautions already 

 pointed out, that the older basalts of Greendale and Bacchus Marsh 

 may be sufficiently closely correlated with those of Maude, Keiloi-, 

 and Royal Park, and with the general mountain-capping basaltic 

 remnants on oui- eastern highlands, to refer them to a period, called 

 the Older Basalt period, and denoting a more or less extensive 

 term of vuljcanicity, which occurred at a time variously estimated 

 as from lower to middle tertiary (Barwonian). This divergence 

 •of opinion as to age is largely due to the uncertainty that exists 

 regarding the age of our fossiliferous tertiaries. 



If these older basalt flows of our eastern highlands had been 

 poured out while the area was still of somewhat high relief — i.e., 

 some time before complete penepl a nation — they would scarcely 

 have been preserved to-day as we now find them. Moreover the 

 valleys whicli these basalt flows have filled and preserved have been 

 investigated in some places and prove to be of mature types. The 

 fact that these basalts in eastern Victoria lie at, or a little above, 

 peneplain level, appears to shoAv that there could not have been a 

 very long interval between uplift of the peneplain and the extru- 

 sion of the basalt. Otherwise we should expect to find these lavas, 

 where preserved, somewhat below the general peneplain level. (See 

 ■also Hart, ref. 22, p. 256.) 



