part 2] OF SOUTHEEN EYRE PENIIfSULA. 113 



support the suggestion previouslj^ made that the quartz- and ortho- 

 clase-bearing amphibolites are derived from doleritc rocks in which 

 quartz and orthoclase figured as constituents, in some cases 

 certainly as micro|)egmatite. 



With this brief treatment of the petrographic nature of the 

 amphibolite members of the Flinders Series, the important subject 

 of source and oris^in remains for consideration. If we confine our 

 attention for the moment to the amphibolites which yield indubit- 

 able evidence of their anterior origin as compared with the granite- 

 gneisses, the evidence on which this is based may be recapitulated 

 as follows : — 



(1) The amphibolites are invaded and broken tip by the granitic and pegma- 



titic veins and dykes. 



(2) These veins may intrude along- well-defined foliation-planes, or break 



abruptly across them. 



(3) The disruption of amphibolite-bands into smaller lenticles and streaks 



can be traced in innumerable examples. 



(4) Wherever the amphibolites possess an elongate habit, their longer axes 



are in general arranged parallel to the flow- structure in the surrounding 

 gneiss, which bends round them at their extremities. 



(5) The amphibolites have in some cases been rendered plastic under the 



influence of the thermal metamorphism, being drawn out in the direction 

 of the flow-structure in the gneiss, and conforming to its intricate 

 contorted foliation. 



This collective evidence is overwhelmingly in favour of these 

 amphibolites being earlier inclusions in the acid gneisses, and any 

 posterior dyke-origin is inadmissible. Two possibilities remain to 

 be discussed : 



(i) The amphibolites are basic segregation-products of the acid gneisses. 



(ii) They represent earlier consolidated rocks Avhich have been previously 

 metamorphosed, and engulfed by the later gneisses. 



Neither by their form nor by their relationship to the granite- 

 gneisses, do these amphibolites correspond to basic segregations^ 

 and any interpretation on the lines of explanation (i) can be dis- 

 missed. That they are earlier consolidated masses which have 

 been metamorphosed and subsequently engulfed hj the granites 

 remains a conclusion supported by all the evidence that now 

 exists. 



In the first place, it is to be remarked that the metamorphism 

 had been accomplished prior to their incorporation, for by this 

 means alone can be explained the fact that these planes of foliation 

 have been utilized as planes of maximum invasion by the liquid 

 magma, thus necessitating an antecedent foliation. 



In accordance with this view is the evidence that the long and 

 narrow bands have their foliation and elongation in parallelism ; 

 for the stoping action that incorporation demands must of necessity 

 have taken place along those directions in which separation was 

 most readily accomplished. Such foliation -planes are thus ])lanes 

 of minimum cohesion. On the other hand, those amphibolites 



