Linibitrglte Mock. 129 



volcanic plugs. Mr. Dennant states that '' Tlie rock is black 

 and so dense that I have not been able to make any section 

 really transparent." He also mentions the specific gravity of 

 the rock as reaching 3. By the courtesy of Mr. R. H. Walcott, 

 F.G.S., we have been able to examine a section of the above rock 

 which was made by Mr. Dennant, and comprised in his collec- 

 tion, Qow at the National Museum. The slide is labelled as 

 from Mount Adam. It closely resembles the Balwyn rock in 

 its great density and general composition ; but, nevertheless, 

 appears rather to belong to the more basic type of the olivine 

 basalts, since the basic oxides are not so abundant, nor the 

 olivines so ferriferous. The Mount Adam rock may be briefly 

 described as follows : — Ground-mass fine-grained, taxopilitic ; 

 composed of finely felted crystals of plagioclase felspars, together 

 with minute tabular and prismatic augites and small crystals 

 of olivine of the second generation, and fairly abundant but 

 minute magnetite crystals. A moderate number of phenocrysts 

 af olivine are scattered through the rock, averaging about 

 .75 mm. in length, and with pale brown decomposition areas 

 along the fracture planes. Also an occasional phenocryst of 

 augite of a pale brown or wine colour. 



The rock forming a volcanic neck at Mount Consultation, near 

 Castlemaine, is described by Dr. T. S. HalU as a *" basalt, almost 

 black, very fine^-grained, rarely vesicular," and having " in some 

 places a platy structure." This rock corresponds in all the 

 above particulars with ours, the platy structure in the Balwyn 

 rock being a very marked feature. 



In South Gippsland, near Anderson's Inlet, there are numerous 

 volcanic necks which have been described by Mr. A. E. Kitson.2 

 Many of these are fragmental volcanic rocks, from which one 

 may infer that explosive action played an important part during 

 their extrusion. Several of the rocks mentioned in detail by 

 Mr. Kitson resemble magma basalts, but since the actual 

 niineralogical composition is not given, it is impossible to say 

 whether they belong to the augites or the limburgites ; the 

 remainder are referred to olivine dolerite and basalt. The 



1 Proc. Roy. Soc. Victoria, vol vii., n.s. (1895), p. 81. 



2 Ibid, vol xvi, n.s., pt. 1. (1903), p. 154. 



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