log THE GEOLOGY OF TASMANIA— THE PRB-CAMBRIAN. 



(b) Schists of Igneous Origin. 



Associated with these quartzites, quartz-mica schists^ 

 arg-illaceous, and micaceous schists are certain amphi- 

 'bolites, to which the writer would ascribe an igneous 

 origin. 



The largest development of these amphibolites is 

 that which has been observed in the Rocky River dis- 

 trict by Mr. W. H. Twelvetrees. 



Less 'extensive occurrences have been recorded from 

 Hamilton-on-Forth and the Collingwood River Valley. 

 In both of these latter cases there is a notable develop- 

 ment of garnet and zoisite. 



The detailed description of these interesting rock 

 types is postponed, pending a more minute micro- 

 scopical examination. 



The only other rocks of igneous origin which may 

 possibly belong to the Pre-Cambrian are certain pegma- 

 tites, which have been found in the Collingwood River 

 Valley and in the neighbourhood of Calder's Pass. 

 There is, however, a very strong probability that these 

 have been introduced into the schist series in Devonian 

 time. 



v.— THE STRUCTURAL FEATURES OF THE 

 PRE-CAMBRIAN. 



Few constant features of structure have been re- 

 corded from the several exposures of these rocks which 

 have been examined. The distribution "is so wide that, 

 in the absence of complete and systematic surveying, 

 this is not 'a matter for surprise. And although much 

 is to be gained by the careful examination of the struc- 

 tural characters of the group as a whole, little achieve- 

 ment has so far been possible in these matters. 



The recognition of any definite horizons in the sys- 

 tem is naturally a matter of importance for purposes of 

 stratigraphical delimitation. 



In the case of the highly schistose and crumpled 

 members of the system, it is almost impossible to arrive 

 at any satisfactory conclusion regarding the total thick- 

 ness of the beds or their original order of stratification.. 



