1-24 '^^^ GEOLOGY OP TASMANIA— THE PRE-CAMBRIAN. 



(c) The Cambrian sediments are in common much 



more free from foliation than normal members 

 of the Pre-Cambrian series. 



(d) Igneous rocks which were formed contem- 

 poraneously with certain of the Pre-Ordovician 

 rocks appear only as intrusive rocks intersect- 

 ing the Pre-Cambrian schists. 



(e) The Pre-Cambrian rocks have been the source 



whence the material of certain of the Cambrian 

 formations (lying stratigraphically at the base 

 of this system) has been derived. 



The writer would therefore submit that the Pre- 

 Cambrian age of certain rocks, described below, has 

 now been satisfactorilv established. 



IV.— TPIE LITHO'LOGICAL CHARACTERS OF 

 THE PRE-CAMRRIAN ROCKS. 



The bulk of these fundamental schists is, beyond 

 doubt, constituted of metamorphosed sediments of 

 aqueous origin ; but there are present also certain com- 

 ponent parts of the series to which an igneous origin 

 would be ascribed by the writer. It is proposed to give 

 a brief description of these separately. 



(a) Schists of Aqueous Origin. 



The evidence upon which the origin of these rocks 

 is affirmed is not equally conclusive in every case. But 

 when any large area, in which these rocks are developed, 

 is examined, the observer cannot but be convinced of 

 the unity of origin of the several varieties which are to 

 be found inextricably interlaminated. 



The greatest weight, in determining the origin of the 

 series, must necessarily be placed upon those varieties 

 which afiford the least questionable evidence. And the 

 varieties which, more than others, possess this quality 

 are those in which original characteristics of composi- 

 tion and texture have been least masked by molecular 

 readjustment and mechanical deformation. These are 

 the schistose consrlomerate'= 



