BY LOFTUS HILLS. M.BE., M.SC. 129 



their proximity to Hobart, must inevitably appeal as a sub- 

 ject of research to an active School of Geology located at 

 Hobart. The most complete description of this series so 

 far published is that by Dr. F. P. Paul, which appeared in 

 1906. (1) 



There now remains to be discussed the advance in know- 

 ledge of the Porphyroid Igneous Complex during the last 

 18 years. The work accomplished in this field is consider- 

 able, as is evident when it is remembered that it is during 

 this period that the conception of this Porphyroid Igneous 

 Complex as a distinct igneous rock series has been gradually 

 evolved. The petrographic studies carried out on the in- 

 numerable varieties of quartz-porphyries, felspar-porphyries, 

 felsites, syenites, granites, etc., occurring in close association 

 on the West Coast have resulted in a gradual separation 

 of a very large group of these igneous rocks which are char- 

 acterised by mineralogic reconstitution and evidence of great 

 physical strain, from a group relatively less plentiful in 

 varieties which possess no internal evidence of such dynamic 

 metamorphic action. To the former group the name "por- 

 phyroid" was applied by G. A. Waller in 1902, and subse- 

 quently this term was adopted as a group name as the 

 result of considerable study by the late Professor H. Rosen- 

 busch,, to whom recognition must here be made of very great 

 assistance in elucidating the petrography of this group of 

 igneous rocks. 



It is a very difficult task, in view of the mineralogic re- 

 constitution and mechanical deformation which this series 

 of rocks has undergone, to recognise the original character 

 of the several rock-types from petrographic study. Gradual 

 progress in description and in deductions as to original 

 character has bsen made, mainly by Twelvetrees, Ward, Pro- 

 fessor W. Gregory, and the writer, and it is now perfectly 

 clear that in this Porphyroid Igneous Complex we have a 

 comagmatic series consisting of effusive, intrusive, and plu- 

 tonic types ranging in composition from basic to acid. There 

 still remains, however, a great amount of work to be done 

 in the petrographic study of an almost unlimited number 

 of varieties of this series particularly in the case of the 

 effusive and fragmental types, and also in connection with 

 the basic plutonics. 



(1) F P Paul: "Beitrase zur petrographischen Kenntniss einiger 

 foyaitisch ' thiralitischen Gesteine aus Tnsmanien" MineraL petr. 

 Mitteil Band 25. Heff IV., Wien. 1906. 



