]gO G. A. Cook: 



Mi( n.scopically the rock from this pavement is .typical of the law 

 level basalt found in the area. Olivine is sparingly present in 

 large, perfectly fresh phenocrysts. Light green augite is very 

 plentiful in smaller crystals. A feature of the rock is the ophitie 

 structure, which this augite shows witli plagioclase needles. These 

 latter are very plentiful, and show typical How-structure. The 

 angle of extinction of the lamellae of a number of laths has a 

 maximum of .SO (leg. This would indicate labradorite. There is 

 also a very slight content of another untwinncd felspar. This has 

 verv low polarization colours, and a very low extinction angle. It 

 iR possibly anorthoclase, which F. L. Stillwell 1 finds in tlie newer 

 basalt at Broadmeadows. An examination of a number of slides 

 would l>e necessary to confirm its presence, The order of crystalliza- 

 tion^ was -olivine first, then plagioelase, and then augite; for large 

 •crystals of olivine are frequently seen completely surrounded by 

 aureoles consisting of ophitie augite and labradorite. 



Oxide of iron is also rather frequent in the rock. The -majority 

 of the crystals are long and needle shaped, and hence most of them 

 are ilmenite. 



Glass, dusty green in- colour, and containing many needles of 

 ilmenite, is also very common. This high glass content is typicaj 

 of the low level basalt in the area. The rock at the pavement 

 also contains a fairly large content of a greenish-brown zoned 

 material filling up what appear to be cavities. Under crossed 

 nicols this material shows low polarization colours masked by the 

 greenish colour of the mineral. No clear interference figures are 

 obtainable, probably due to the material being an aggregate of 

 small crystals. It is faintly pleochroie. Another characteristic is 

 that it is invariably associated with the glass in the rock. It is 

 probably chlorite. 



1 I'roc. Roy Soc. Victoria, x\iv. (n s.), Pt i., p. 1 Hi, 111! 1. 



