Palaeozoic Geilogy oj Victoria. 141 



therefore Lower Devonian. They appear to be metaso- 

 maticallv altered igneous rocks, varying from andesitic 

 to more acid types. Tliough widespread in their dis- 

 tribution, each occurrence appears to be small in ex- 

 tent. 



(2) The oldest sediments in this region are regarded as Upper 



Ordovician. Definite graptolites were found in four 

 distinct localities, and there does not appear to be any 

 valid reason, structural or lithological, to justify the 

 separation of any of the non-fossiliferous portions from, 

 those yielding graptolites. 



(3) Ihe igneous series known as the Snowy River Porphyries, 



is regarded as Lower Devonian, and rests uncomform- 

 ably on the Upper Ordovician sediments. The chief 

 additions to previous knowledge concerning this exten- 

 sive igneous belt are : — 



(a) Tlie recognition of porphyroids. 



(b) Finely stratified ash beds. 



(c) The occurrence of tracliytic and andesitic rocks. 



(d) The fact that the so-called quartz-porphyries are 



really quartz-porphyrites, triclinic felspar pre- 

 dominating. Two analyses of this type are 

 given, 

 (c) A soda rich tyjie is described as a quartz-cerato- 

 phyre. Both microscopically and chemically it 

 is shown to be closely similar to certain rocks 

 described by Howitt from Xoyang, as quartz- 

 porphyrites, and later referred to by Skeats 

 as ceratophyres. 

 (f) The chemical characters and petrographical re- 

 lationships of the igneous rocks are discussed, 

 and it is shown that the porphyi-ites are genetic- 

 ally related to the alkali granites, which are 

 characteristic of this part of Victoria. 

 Making use of a variation diagram to compare tiie 

 various acid igneous rocks of Victoria, it is seen that 

 the quartz-porphyrites of the Tara Range, and the alka- 

 line granite of Gabo Island, etc., conform closely to 

 the graphs occupying the opposite end to that of the 

 dacites and granodiorites. It would appear, therefore, 

 that the acid rocks of the Snowy River Series belonfr tc 



