142 THE PROGRESS OF GEOLOGICAL RESEARCH IN TASMANIA, 



During the summer of 1919-20 A. Mcintosh Reid carried 

 out a very thorough investigation of the occurrences of osmi- 

 ridium in Tasmania, and his bulletin dealing with the ques- 

 tions of composition, mode of occurrence, and genesis is now 

 in the Press. In this bulletin the differentiation of the basic 

 phase of the Epi-Silurian plutonic period is studied in de- 

 tail, and it is shown that the osmiridium is confined to the 

 ultra-basic olivine-rich differentiates now converted to ser- 

 pentine. It is further shown that the distribution within 

 the serpentine masses is controlled by the occurrence of de- 

 finite contraction fissures. 



(13) Ore Deposits of Various Districts. 

 In addition to the ore deposits in the districts mentioned 

 above which have been investigated in detail, there are a very 

 large number of isolated deposits which have been subjected 

 to more or less complete examinations without completely 

 elucidating their relation to the general geology. It may 

 rn fact be claimed that we possess a good general knowledge 

 of the miner alogic composition of the great majority of the 

 ore-deposits of Tasmania. It cannot, however, be claimed 

 with equal justification that either the structural features, 

 paragenesis, or genesis of the deposits, other than those 

 specifically mentioned above, have yet been completely 

 elucidated and described. It is certainly a fact, however, 

 that sufficient m.aterial is available, either published or un- 

 published, to enable such an elucidation and demonstration 

 to be effected, and the writer is attempting this undertak- 

 ing in his work on "The Metallogenic Epochs of Tasmania." 



(14). Metallogenic Epochs. 

 It was recognised by the late W. H. Twelvetrees in 1909 

 that there have been at least two metallogenic epochs — one 

 genetically associated with the porphyroid petrogenic cycle, 

 the other with the Epi-Silurian batholithic epoch. Since 

 that date additional material for the genetic classification 

 of our ore-deposits has been acquired, and the writer is pre- 

 senting such a complete genetic classification in his above- 

 mentioned work, in addition to demonstn:ating the various 

 phases and zones of the several metallogenic epochs. 



IX. SOME PROBLEMS AWAITING SOLUTION. 



(1). Areal Mapping. 

 The total area of Tasmania is 26,215 square miles. The 

 areas of which geological maps have been made as the re- 



