1 32 Chapman and Thiele : 



In the sequel to this paper the analj'ses of the Bendigo and 

 the Woodend rocks are quoted, where it will be seen that the 

 former is richer in lime, but otherwise they agree pretty closely, 

 especially in the percentages of the basic elements. 



Suggestions and Conclusions as to the Age and 

 Relationships of the Volcanic Pipe at Balwyn. 



The presence of basic lava in this locality leads us to look 

 around for similar ocurrences, but without avail. Basalt occurs, 

 it is true, to the N.W. of Heidelberg, and to the W. of Balwyn 

 at Collingwood ; but in these instances the lava is found as more 

 or less continuous sheets filling up former river courses. They 

 are, 'moreover, easily recognisable as typical lava flows of the 

 younger, or newer volcanic, series. 



The decomposed state of the lava and its comparative isola- 

 tion, as well as its almost identical chemical and physical com- 

 position, as compared with well-recognised lavas of the older 

 series of basalt flows, compels us to place this occurrence in the 

 same category. It is here apposite to remark that Professor 

 Skeats has referred his recorded limburgite occurrence at Wood- 

 end to the same series of the older basalts, for he gives the 

 sequence of the alkali series of " (?) middle cainozoic " age as^ 

 ranging from solvsbergite, etc. ... to limburgite and 

 newer basalt.^ 



As regards the age of the greater part of the flows and vents 

 of the older basalt, the argument for their being miocene (i.e., 

 janjukian) is strongly supported by their intercalation between 

 beds of janjukian age on the Victorian coast,2 and along the 

 Moorabool Valley. The position and local occurrence of the- 

 Balwyn limburgite plug points to the probable conclusions that, 

 assuming it was formed in miocene times (i.e., janjukian), it 

 either cooled considerably below the original surface of the 

 Silurian bedrock, and was afterwards exposed when the Koonung- 

 koonung Creek basin was carved out by kalimnan or post- 



1 President's Address, Section C, Austr. Ass. Adv. Sci., Brisbane, 1909, p. 203. 



2 See Note on the Geology of the country about Anglesea. T. S. Hall, Proc. Roy. Soc 

 Victoria, vol. xxiv., n.s., pt. 1 (1899), p. 49 et seq. 



