BY LOFTUS HILLS, M.li.E., M.St'. 121 



Since that date it has been satisfactorily demonstrated 

 that the Porphyroid Igneous Complex, the Read-Rosebery 

 and Lyell schists, and the Dundas slates and breccias are 

 separated from the Silurian sedimentary rocks by a period 

 of very pronounced diastrophism. As explained above, these 

 older rocks are referred to as Cambro-Ordcvician. The 

 series which are now definitely recognised as belonging to 

 the Silurian system are the slates and sandstones of the 

 Queen River, Zeehan, and Middlesex, and other localities 

 on the West Coast; and the blue limestone, generally known 

 as the Gordon River limestone, but which occurs at numerous 

 localities throughout Northern, Western, and Southern Tas- 

 mania. Suites of fossil remains from these series have been 

 examined by W. S. Dun, whose final conclusion was 

 to the effect that the species of the various genera v/ere of 

 Silurian types, but possessed to some extent an Ordovician 

 facies. On the whole, however, this paleontologist con- 

 cludes that both series are of Silurian age, and most pro- 

 bably Lower Silurian. 



And now it is necessary to mention a sedimentary series 

 which is such a prominent factor in West Coast geology, 

 and which has been the subject of much discussion and 

 investigation, being within the last 18 years referred to 

 systems ranging from Devonian to Cambrian. The series 

 referred to is the West Coast Range Conglomerate Series. 

 This series was referred by tha late W. H, Twelvetrees 

 in 1902 t3 the Devonian, and L. K. Ward, mainly on nega- 

 tive evidence, transferred it in 1909 to the base of the Cam- 

 brian system. The negative evidence referred to consisted 

 of the non-discovery within the conglomerate of pebbles of 

 rocks of the Porphyroid Igneous Complex. The discovery 

 in 1913 by the writer of numerous pebbles of such rocks in 

 the conglomerate series as developed in the Jukes-Darwin 

 field showed the uncertainty of basing conclusions on 

 negative evidence, and finally determined the Pcst-Porphy- 

 roid age of the conglomerate series. Investigations carried 

 out since that time by the writer, and which are still in pro- 

 gress, have supplied abundant confirmatory evidence. 



The age of the West Coast Range Conglomerate Series 

 is by this succession shown to be Post-Cambro-OrdDvician. 

 The study of the structural geology of this series and the 

 Silurians, v/hich has been carried out in the Zeehan field 

 by G. A. Waller, and by the writer on the greater part of 

 the West Coast Range, serves to strengthen to almost cer- 

 tainty the conclusion arrived at by G. A. Waller in 1903, 



