122 THE PROGRESS OF GEOLOGICAL RESEARCH IN TASMANIA, 



that the West Coast Range Conglomerate conformably un- 

 derlies the Silurian limestone series, and is itself of Silurian 

 age, constituting, in fact, a basal conglomerate series of 

 the Silurian system in Tasmania. 



The much-discussed Tubicclar or Pipe-Stsm Sandstone 

 belongs to the uppermost horizon of the West Coast Range 

 Conglomerate Series, and is more highly developed in the 

 North than in the more southerly portion of the known oc- 

 currences. The limestone immediately succeeds this Tubi- 

 colar Sandstone, and is itself conformably overlain by the 

 slates and sandstone series, the Silurian system in Tasmania 

 thus consisting of: — 



(3) Slates and Sandstone series of Queen River, 

 Zeehan, Middlesex, etc, 



(2) Limestone series of Gordon River, Railton, etc. 



(1) West Coast Range Conglomerate series. 



(4). Devonian. 



There are no sedimentary rocks so far located in Tas- 

 mania which can be referred to the Devonian system. 



Consequent on the collapse of the gecsynclinal in which 

 the Silurian sediments were laid down, there ensued an 

 orogeiiic period of considerable intensity. This orogenic 

 movement consisted largely of folding, but thrust faulting 

 on a considerable scale was a marked characteristic. It is 

 this erogenic folding and faulting which is responsible for 

 the very complicated relationships betvv'^een the older rocks 

 and the Silurian sediments which have been the cause of so 

 many misinterpretations of the geological succession. 



The final phase of the orogenic period consisted of the 

 irruption of the principal granitic rocks of Tasmania. The 

 fact that the next sediments ta accumulate are of Permo- 

 Carboniferous age, and that they rest in many cases directly 

 on the granite, points to the conclusion that during the 

 Devonian period Tasmania was a land surface, and was 

 subjected to a prolonged cycle of denudation. In fact, work 

 recently carried out by the writer has shown that at the 

 close of the Devonian period this land surface had bsen re- 

 duced to a peneplain. 



( 5 ) . Permo-Carboniferous. 



An important advance in our knowledge of the Permo- 

 Carboniferous system was made by the late W. H. Twelve- 

 trees in 1911, when he demonstrated that the Tasmanite 



