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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [N-OV. 4, 



line separating that colony from Victoria, is crateriform, and is in the 

 midst of a low, flat, and sandy district, with low ranges of tertiary 

 limestone. I am not aware whether it has erupted much lava. 



It is impossible at present to define the exact limits of the areas 

 occupied by the most recent volcanic rocks, or perhaps always to 

 determine the age of the various basalts or lavas ; but we may draw 

 some useful general conclusions, nevertheless, from the information 

 already accumulated. 



Over nearly the whole extent of Victoria there are masses of in- 

 trusive basalt, in some places columnar, in others in rude angular 

 blocks, breaking through both the granite and the palaeozoic strata, 

 which clearly, from the mode of their occurrence, are unconnected 

 with the recently-extinct volcanos. Such masses are often found in 

 close proximity to the newer basalt, as at Melbourne ; and of these 

 Mr. Selwyn's descriptions are most excellent. He draws a proper 

 distinction between the older, close-grained basalt, as it generally 

 occurs, much decomposed, and of a nodular structure, and the re- 

 cent rock, which is commonly very vesicular and amygdaloidal * . 

 From the similarity in lithological character, as he observes, it is, 

 however, sometimes impossible to separate the one from the other. 

 I have seen the newer basalt, in close proximity to a crater, both 

 vesicular and very dense, and the latter undistinguishable from some 

 specimens of undoubtedly older rock. Neither from their mineral 

 constituents nor specific gravity is it possible to say, from a hand- 

 specimen, whether the basalts are new or old. The following 

 section (fig. 4) shows, in a synoptical form, the manner in which these 

 formations occur. 



Fig. 4. — Diagram showing the relations of the Basalts in Victoria. 



a. Porous lavas (recent), b. Younger basalts, c. Older basalts, d. Quartz- 

 ose drift (Pleistocene ?). e. Tertiary fossiliferous strata (Miocene ?). 

 /. Palaeozoic rocks, g. Granite. 



The older basalt, c, in all probability, was erupted by submarine 

 volcanos ; and we have no reason to suppose that it did not flow 

 in considerable streams, and fill up inequalities in the ancient sea- 

 bed. Extensive denudation (of which during that period we have 

 abundant proofs) would account for the removal of the cappings or 



* See Geological Surveyor's Report (p. 7). 1854. 



