202 



PRESIDENT S ADDRESS SECTION C. 



A basalt from Flinders somewhat resembles the last but is 

 coarser in grain and has larger phenocrysts of olivine. 



The highly decomposed basalt in the Royal Park cutting contains 

 unweathered nodules (134), which when sliced present considerable 

 resemblance to the newer basalts of the Melbourne district. It is a 

 medium-grained ophitic-olivine basalt with large olivine phenocrysts,. 

 brown, irregular augites, magnetite, lath-shaped plagioclase and a 

 little residual interstitial felspar of a more acid character, and which 

 may be in part orthoclase. 



Tlie basalt from the Berwick quariy is a very coarse grained 

 rock. Olivine phenociysts are large and abundant, the augite is 

 purplish-brown and probably titaniferous, ilmenite and magnetite are 

 common and two types of felspar occur, a lath-shaped plagioclase and 

 a residuum of a more acid felspar. It is really an ophitic olivine- 

 dolerite. A rock from Konimburia is even coarser in grain, and more 

 felspathic. Olivine is not present. Pale augite and a brown hornblende 

 occur sparingly as phenocrysts. Miigiietite is present, but the 

 dominant minerals are the felspars, of which the phenocrysts occur 

 as broad plagioclase crystals showing zoning, and a more acid type 

 as a colourless ground mass in which prisms of apatite are embedded. 



A rock from the Bacchus ]\Iarsh district occurs on the horizon of 

 the older basalts, but the section is seen to have the fine-grained 

 almost felted ground mass and zoned plagioclase phenocrysts 

 characteristic of the andesites. A pale augite and magnetite are also 

 present, and the rock is best described as a basic augite-atidesite. 



As far as I know no recent analyses have been made of the older 

 basalts, and the only two I can find are Howitt's analysis of the 

 tacliylyte from Tangil and one of an older basalt from PhilKp 

 Island, quoted in Selwjni's Catalogue of Rock Specimens and Minerals 

 in the National Museum, Melbourne, 1868. 



These two analyses are quoted below. 



