Palaeozoic Geology of Victoria. 119 



(i.) Fragmental Tijpe. — Sections of this type show all the larger 

 jniiierals and inclusions as broken/ and angular fragments, with no 

 €mbayment. The base is siliceous and finely granular, and among 

 the larger fragments felspar is often more abundant than quartz, 

 and tl),e triclinic form distinctly predominates, orthoclase being 

 rare. 



The secondary minerals most abundant are chloritei, and occasion- 

 ally calcite. 



(ii.) Acid rorphi/rites (Xon-Frar//nefitaf). — The rocks of this type 

 liave perhajDs a higher silica percentage than normal porphyrite, 

 and this may in pai't be due to a certain amount of secondary 

 silicification and alteration. 



The fine grained base of the rock is generally affected to some 

 extent in this way. All the recognisable felspars, however, are domi- 

 nantly triclinic, orthoclas^e being more or less rare. 



No. 100 is a medium grained porphyritic rock of a red brown 

 •colour. 



In the thin section the plienocrysts have rather irregulail outline, 

 the quartz is partly rounded, and occasionally embayed. The fels- 

 pars are more abundant than quartz, and occasionally have a 

 regular prihinatic outline, but more often are broken and irregular. 

 'Twinning after the albite law prevails, but occasional pericline and 

 ■ Carlsbad types are represented. The twin lamellae vary from mode- 

 rately broad to fine bands. Different kinds of felspars appear there- 

 fore to be represented. Only a few were satisfactory for deter- 

 mination by extinction angle. These gave readings up to 20 

 ■degrees, and are probably therefore andesine. 



The oj^tical features of several examples suggest anorthoclase, 

 and the chemical analysis further points to some potash felspar, 

 which, however, has not been definitely recognised microscopically. 

 Magnetite is only moderately abundant. The base is micro- to 

 crypto-crystalline, with some evidence of recrystallisation and sili- 

 cification. Minute laths and fragments of felspars and quartz are 

 scattered through it. 



Chlorite is sparsely distributed through the rock, and calcite is 

 present in moderate amount. 



This rock is regarded as a quartz porpliyrite. No. 105 is a green- 

 ish porphyritic rock, but the chemical analysis corresponds closely 

 with that of the previous example. 



The thin section is very similai-. Quartz plienocrysts are a little 

 jnore abundant, and some are Ixautifully cml>ayei]. The felspars 



