48 J. T. Jutson : 



The Greensborough Older Basalts. 



These rocks t'orni a series of small isolated patches oil the tops of 

 the hills on each side of the Plenty River in the neighbourhood of 

 Greensborough and Janefield. They Avere mapped in the early days 

 of the Victorian Geological Survey, and were re-examined by the 

 writer whilst mapping the country to the east of the Plenty River 

 prior to his departure in 1911 for Western Australia/' Associated 

 with them are the Kainozoic gravels and sands shown on the Survey 

 Quarter-Sheet. As already noticed, Aplin and Hart doubt whether 

 the basalts rest upon the sediments. At the time of my examination 

 of the country, no sections were available showing the actual rela- 

 tions, but from an exhaustive examination I have no doubt that the 

 liasalt overlies the sediments.- This opinion is based upon the 

 relative positions of the two rocks throughout the area, but it is 

 supported by the fact that no l)asalt pebbles in the sediments have 

 been discovered by the writer. If the basalt were the older, we 

 should certainly expect some of its pebbles to be included in the 

 sediments. 



If the relations between the rocks be as stated, then the age of 

 these Kainozoic sediments becomes an important question as regards 

 the correlation of the basalt, and merits some attention. 



Generally similar sedimentary rocks are found to the south in 

 isolated patches, forming as a rule the caps of hills, such as at 

 Heidelberg, Preston, Northcote, Studley Park and Royal Park. 

 These appear to pass into the more or les'fe continuous sheets to the 

 south-east of Melbourne, and there can be little doubt that the whole 

 of these rocks were originally unbroken on the Nilumbik Pene- 

 plain,^ the more northern areas probably being of fresliwater 

 origin, whilst the southern ones aie in part at least marine. The 

 country has since been much dissected, especially in its northern 

 parts, with the result that the sediments in places now form merely 

 the caps of the hills. 



The sediments of tlie Greensborough area are now disconnected 

 I)y erosion. I)ut are found high up the liills at apparently the same 



1 Portion of this counti-.v h;is, I uiiderstaiirt ffoiii Prof. Skeats, lieeii independently inapp>-d 

 liy Sir. Junner of tVie Melbourne Univer.sity (he beinff unaware of my work amongst the basalts of 

 the district), and a paper thereon has been read by him before this Society. At the time of writini;- 

 (Otli .March, 191S) this paper has not been published, nor lias it been seen by me, so that both 

 Mr. .lunner's and my own eonc'lusions are each independent of the other's. 



■2 In places the basalt rests directly on the Silurian. The e.xplanation is that either from tlie 

 contour of the country, the gravels and grits never covered these particular places, or that t hex 

 liave been removed by deiuidation before the flow of the basalt. 



3 Kor a deflnition of this peneplain, see the writer's paper on the Physiography of tlie Yaira 

 previously cited, p. 477. 



