210 president's address SECTION c. 



the Geolo^cal Survey of Victoria. He identifies the felspathoid as 

 hauyn, and it occurs interstitially as a residuum between plagioclase 

 crystals in a very coarse type of olivine-augite-dolerite occurring' as 

 boulders in the tuffs at the base of the series at L. Bullenmerri. The 

 occurrence of this felspathoid-bearing dolerite among the rocks of the 

 newer basalt is interesting. It is the first record for Victoria for this 

 series, and it raises the interesting question of the possibility of the 

 earlies't eruptions in the western district being contemporaneous with 

 some of those from the alkali series of Macedon and Coleraine. 



From the normal calcic basaltic rocks, microscopic description of 

 a few types will suffice to indicate the lange in texture and com- 

 position in this series. The pyroclastic roci^s may be represented 

 by a tuff from Lake Burrumbeet, near Ballarat. In section the 

 fragmental character is clear. The fragments consist of ophitic basalt, 

 of a veiy amygdaloidal glassy basalt, and of a yellowish-green glass 

 resembling palagonite, while secondary calcite fills some of the cavities 

 in the rock. 



Rocks approaching tachylytes occur in places as a thin selvage to 

 flows where they have been quickly cooled. A specimen from the 

 Lai Lai Falls between Geelong and Ballarat consists of lath-shaped 

 plagioclase crystals, a little olivine, and some secondary calcite in 

 a dense brown isotropic matrix of glass. 



A rock from Hepburn Recreation Reserve, near Daylesford, may 

 be taken as an example of a basic and fine-grained basalt. A fair 

 amount of brown glass remains, and this, with minute lath-shaped 

 augites and plagioclase, with magnetite grains, constitutes the ground 

 mass, in which phenocrysts of augite and olivine are embedded. 



The basalt of Mount Franklin, near Daylesford, may be taken 

 as a type of a fine giained but poi^phyritic basalt. The ground 

 mass consists of lath-shaped plagiolase, granular augite and magnetite 

 grains. The phenocrysts consist of moderate-sized crystals of pale 

 augite and olivine and very large crystals, up to 3 in. in length, of a 

 clear glassy variety of oligoclase. 



At the Melbourne Corporation Quarries at Clifton Hill several 

 flows of basalt occur and are quarried extensively for road metal. 

 They show considerable textural differences. The rock from the 

 lowest flow, about 120 ft. below the top of the quarry, is a medium- 

 grained olivine^basalt with pale augite, ilmenite and magnetite and 

 plagioclase laths included ophitically in augite. There is in places a 

 sheaf-like and in others a fluidal arrangement of the felspar laths. 

 Contrasted with this is the rock of the top flow, which is distinctly 

 columnar and coarse grained. It is best described as an ophitic 

 olivine-dolerite. Olivine and large brown augites and iron oxide occur 

 as phenocrysts. The felspar is of two types, lath-shaped crystals 

 enclosed in augite and big broad plates of a fairly acid plagioclase, 

 but showing marked zoning. A little interstitial felspar may be 

 orthoclase. 



