Palaeozoic Geologij of Victoria. 128 



that of Gabo Island, falling therefore into the group of Victorian 

 alkali granites in contrast to the more calcic type of the grano- 

 diorites. An analysis of the Gabo Island granite is included in the 

 table for general comparison with those of the quartz-porphyrites 

 of the Tara Range, and the similarity chemically is vqry note- 

 ■\vorthy. 



With regard to the Snowy River Porphyries generally, much more 

 field work combined with chemical and petrological research is 

 necessary before any satisfactory coilclusions and generalisations 

 can bei made concerning many interesting petrological problems in 

 this area. It is a region which offers splendid scoj^e for future 

 research, and it is perhaps remarkable, as Professor Skeats has 

 already observed, that the late Dr. Howitt having done such valu- 

 able preliminary work in this series, never returned to it. For- 

 tunately, the collection of his rocks and thin slices, together with 

 his field notes, are in the possession of the University of Melbourne, 

 and it has been of considerable help in connection with certain petro- 

 logical points, to be able to compare my own slides with some of 

 those of Howitt's from adjacent areas. 



It is clear, however, that compared with the very careful detailed 

 work, both chemical and petrological, given by Howitt to such areas 

 as Noyang, Swift's Creek, Omeo, etc., this region received very 

 scanty petrological attention, and most of the slides would seem 

 to be among some of his very earliest work in this direction, and 

 are often too thick or too much altered for. very satisfactory deter- 

 minatiion. 



One of the most interesting j^oints, brought out as my own petro- 

 logical study of these rocks proceeded, was the predominance of 

 triclinic felspar among the phenocrysts of the acid porphyritic 

 rocks, especially as Howitt had emphasised the reverse, namely, that 

 monoclinic felspars prevailed. On referring, therefore, tq the par- 

 ticular slides, which he had mentioned in this connection, it was 

 clear that these early determinations of his required some correction 

 and qualification for all the identifiable phenocrysts Avere certainly 

 plagioclase. On account, however, of the decomposed state of the 

 rock, some of the felspars were too kaolinized for determination. An 

 important point, therefore, is raised, as to whether this feature con- 

 cerning the felspars applies to the porphyries of this series as a 

 whole. If so, then it may be possible to distinguisli petvologically 

 between these and certain other porphyries, macroscopically similar, 

 but belonging to the Upper Palaeozoic of the Wellington Series. 



