Ii/ncoiis Rocks. 27 T 



about two miles alnng the Don road, nortli of Launcliinf; Place. 

 The rock is very tough and fine grained, and felspar is the only- 

 mineral visible niegascopically. 



A thin section of the rock examined under the microscope, con- 

 sisted of phenocrysts of felspar in a fine-grained andesitic ground 

 mass of laths and stunted prisms of plagioclase, microcrystalline 

 quartz and magnetite dust. Chlorite, sericite and epidote (pistacite) 

 are alternation products. Original femic minerals are lacking. 



Recrystallisation has taken place in the ground mass of tha 

 original rock, and a mosaic of quartz grains has been formed. 

 Occasional vesicles filled with chlorite and quartz ai*e also present. 

 The panidioniorpliic plagioclase phenocrysts are well zoned, and 

 give maximum symmetrical extinction angles of 36o from the albite 

 lamellae, indicating plagioclase near labradorite-bytownite (Ab?, 

 Ang). Most of them are highly sericitised, and a little secondary 

 epidote has been developed in the felspar in places. The ground 

 mass laths are generally only simply twinned and are referable to 

 labradorite. 



Section No. H2, from near Wade's Look-out, is a fine-grained 

 andesite consisting of zoned phenocrysts of rather basic labradorite, 

 and chloritisecl femic mineral, in a pilotaxitic ground mass com- 

 posed of plagioclase laths, biotite, chlorite and ilmenite. Quartz 

 is absent. The section of this rock is very similar to sections of 

 certain black andesitic xenoliths present in the dacites. 



►Section No. H79, biotite andesite, M.M.B.W. pipe line to Badger 

 Creek Weir. — A thin section of the rock examined microscopically 

 shows abundant phenocrysts of zoned plagioclase (andesine or acid 

 labradorite). chloritised biotite and ilmenite in a yellowish coloured 

 devitrified glassy ground mass. Quartz is almost entirely absent. 

 Abundant granular ilmenite occurs, included in biotite, and in the 

 ground mass of the rock some of the ilmenite is replaced by pyrites. 

 A little epidote replaces biotite. 



A Pyroclastics. 



Section iitar Wade's Look-out. — The best section of these frag- 

 mental rocks, in the area described, occurs in cuttings along the 

 Don road from Healesville to Launching Place, above Wade's Look- 

 out. Near the Look-out, the pyroclastics are seen resting on east- 

 dipping Silurian sediments. The former consist here of tuffs, and 

 volcanic agglomerates containing rounded and sub-angular pebbles 

 of rhyolite or quartz porphyry. About one-third of a mile above 



