134 



as to give superpositions within the thickness of the slide, so 

 that measurements cannot be satisfactorily made. This fel- 

 spar is granophyrically intergrown with quartz. 



Oligoclase is also present in fairly idiomorphic crystals 

 which show no sign of mechanical strain. Round the edges 

 of some of the oligoclase crystals there is a pegmatitic -nter- 

 growth with quartz. 



Quartz grains are fairly large. All show strain effects 

 from undulous extinction to complete shattering. 



Biotite present in small amount, pleochroism from dark- 

 green-brown to yellow, shows dark halos round included 

 zircon. Muscovite very scarce. 



A little apatite is scattered through the rock. 



Railway line bet^veen Callington and Monarto, at 

 the forty-eight mile post. Biotite schist. Perfectly granular 

 with very fine grainsize. Thoroughly schistose. Light and 

 dark constituents about equally abundant. The former in- 

 clude chiefly quartz and acid felspar. Recrystallization is 

 complete, and there is no trace of undulous extinction. The 

 felspar is almost entirely untwinned. 



The dark-coloured material is chiefly biotite of a clove- 

 brown colour. 



There is a notable amount of muscovite present in largish 

 flakes whose lengths lie across the schistosity. 



As accessory minerals Ave have a little tourmaline with 

 pleochroism colourless to brown, and a little zoisite in rounded 

 igrains. No garnet is to be seen. 



Near Kanmantoo, Biotite schist. — Finely granular and 

 completely schistose. Quartz and biotite are the most 

 abundant constituents, the latter being dark-brown. A little 

 untwinned acid felspar is present, but much less than in any 

 of the other rocks so far described. There are grains and 

 flakes of magnetite and a few microscopic garnets; also an 

 occasional prism of rutile. A fair amount of muscovite is 

 present in porphyritic flakes lying across the schistosity and 

 containing ovules of quartz. 



First Railway Cutting west of Callington. Chlorite 

 schist. — The texture is markedly porphyritic, the grainsize 

 of the base being uniform and fine (about '025 mm.). 



There is no felspar discernible in the base, which is 

 essentially composed of thoroughly granular quartz and brown 

 biotite, with subordinate amounts of muscovite and ilmenite. 

 Biotite and ilmenite both have extremely minute orange webs 

 and rosettes of "'sagenite" like those above described (p. 133), 

 but on a much finer scale. There is a little tourmaline and 

 a fair amount of rutile also. The rock is rendered porphyritic 

 by clinochlore in irregular flakes up to about 1*5 mm. across 



