Geology of Mount Macedon. 197 



with liiiionite. Clilorite is present as an alteration product after 

 the hypersthene. The base has a well developed fluidal structure 

 shown by the arrangement of the plagioclase laths ; it contains 

 patches of material of an earlier consolidation in which the 

 structure is pilotaxitic or subgranulitic. 



Hence this rock agrees in composition with the Williinigongong 

 type and began to solidify under the same conditions ; l)ut its 

 final consolidation occurred after it had undergone a definite 

 flow. 



l>. The Trachy-Phonolites. 



The rock (No. 28) that crosses the valley of the Turritable 

 Creek and forms the waterfall a little to the west of the State 

 school at Upper Macedon is the most convenient type of the 

 trachy-phonolites. 



The rock is dark gi'een in colour, and is porphyritic, with 

 large phenocrysts of anorthoclase, showing the typical minute 

 twinning of that species. The base is full of fluidally arranged 

 felspar laths, which are either simply or repeatedly twinned. 

 They also are probably anorthoclase. Sparsely scattered through 

 the rock are small crystals of aegerine, which show the typical 

 pleochroism of green and greenish yellow ; they are about 

 as long as the longer felspar laths in the base. Between the 

 laths is a somewhat altered green glass, which in places is 

 arranged in vermiculitic growths and elsewhere occurs as radial 

 globules, which show a black cross under crossed nicols. An 

 isotropic mineral, which gives some hexagonal sections, and the 

 green glass both give gelatinous silica when treated with hydro- 

 chloric acid. Evaporation of acid that has acted on this mineral. 

 Mineral yields a few gypsum crystals, so that it is no doubt 

 nosean. Ilmenite in large flakes is sparsely scattered, but in 

 places it occurs in clots. 



This rock has been analysed by Mr. R. J. Lewis ; the analysis 

 (No. 2, p. 201) in conjuction with the microscopic evidence shows 

 tliat the rock is a trachy-phonolite. 



Another exposure of this rock (No. 33) occurs in a small 

 quarry to the south of the waterfall and near the junction with 

 the undei'lying Ordovicians. The rock is porphyritic and hyalo- 

 pilitic in structure. It contains phenocrysts of anorthoclase 



