1 2 8 Chap man and Th Ide : 



Microsropic Characters of the Baric-green Lava. — The general 

 structure of this rock is much the same as the darker, normal 

 variety, but it has undergone nmch secondary change. The 

 olivines are hirgely serpentinised, and the more ferriferous are 

 changed into a substance like iddingsite, which shows marked 

 pleochroism and prismatic cleavage cracks. Magnetite is very 

 abundant in this rock. 



The above rock is a fairly typical limburgite,! olivine and 

 augite both being present, the latter forming a large proportion 

 of the ground-masS; whilst the felspar is comparatively rare. 

 By its mode of occurrence this rock, as Prof. Skeats has kindly 

 pointed out, seems to be related to the monchiquites, but it is 

 not typical, seeing that neither biotite nor hornblende occur 

 in it. (See footnote at end of paper). 



The specific gravity of this rock at 4 deg. C. is 2.994, as deter- 

 mined by Mr. P. W. G. Bayley, Assoc. S.A.S.M., of the Victorian 

 Mines. Depai'tment Laboratory. We are also indebted to that 

 Department for the analysis of the Balwyn rock, prepared by 

 Mr. Bayley. For comparative purposes the analyses of the 

 Woodend and Bendigo examples are also appended (see last 

 page). 



Notes on some Previously Recorded Occurrences 

 of Volcanic Plugs of a Basic Character. 



Volcanic plugs and necks have been recorded from several 

 widely separated localities in Victoria, as, for example, near 

 Coleraine, near Castlemaine, at Anderson's Inlet, and at Wood- 

 end. 



The two conical hills near Coleraine, known as Adam and Eve, 

 which were noted by the late Mr. Dennant,"^ are in all probability 



1 The best known British example of liniburgite is perhaps that from Whitelaw Hill, near 

 Haddin^'ton, described by \)v. F. Hatch (Trans. Roy. Soc. Edin., vol. xxxvii., 1S9'2, pp. 116, 

 117, pi. I., fig'. 1). It closely resembles the Balwyn rock in its mineralojjical and chemical 

 composition, the silica beinjj in the jiroportion of 40 per cent., and the magnesia 12 per 

 cent. Its specific gravity is 3.03. A specimen from the type locality of Limburg, 

 described by Rosenbusch, gave a specific gravit3' of 2.829 (See Cole, G. A. J. — "Aids in 

 Practical Geology," 1891, p. 241). 



2 Rep. Aust. Assoc. Adv. Sci., 1893, Adelaide, p. 395. Mr. E. G. Hogg refers to the same 

 rock as an olivine basalt (Proc. Roy. Soc. Victoria, vol xii., n.s.. 1899, p. 91). 



