74 Proceedings of the Royal Society of Victoria. 



augite phenocrysts present peculiai'ities of another kind ; there is 

 an inner area, often with ragged, uneven boundary, which is clear 

 and colourless in plane light ; this is enclosed in a border of a light 

 brown colour and of varying breadth ; the Avhole is enclosed in 

 augite showing good crystal outlines. The inner area does not, 

 in general, obscure with the outer area ; it is more highly 

 refracting. The enclosed material is in all probability an eroded 

 augite crystal. Most of the augite crystals show accumulations 

 of black specks towards their centi'al parts. Olivine is present 

 in large crystals, but has suffered much decomposition ; the 

 replacing material is light green in colour and sometimes faintly 

 pleochroic. "When decomposition has advanced very far the 

 olivine has been entirely converted into a serpentinous material. 

 There is no mica present in the slide ; in another slide, procured 

 near Mount Bullengarook, there are small patches of a reddish- 

 brown mica, pseudomorph after olivine, which may possibly be 

 rubellan. The mica seen on the surface of the rock from which 

 this slide has been cut appears to occupy a cavity in an olivine 

 crystal. The residual glass is in places traversed by long, colour- 

 less, acicular rays. Beyond the fact that they are a common con- 

 stituent of basalts all over the globe, nothing definite appears 

 to be known of them. Zirkel, in his " Microscopic Petrography 

 of the Fortietli Parallel," regards them as an undetermined 

 product of devitrification. Having regard to the basic character 

 of the rock and the absence of felspar crystals, we have no hesita- 

 tion in calling it limburgite. The previous occurrence of this 

 mineral in Victoria has been noticed by Mr. A. W. Howitt in a 

 dyke in the No. 180 Mine, Bendigo. 



