1^6 THE GEOLOGY OF TASMANIA— THE PRE-CAMBRIAN. 



stone on the higher country ; or, again, local displace- 

 ments of the crusts may give rise to modes of occur- 

 rence which may seem at variance with this theory. 

 Yet, in the case of the occurrences of limestone in the 

 valleys of the Jane and Denison Rivers, at least, we 

 seem to be forced to the conclusion here stated. It will 

 be interesting to ascertain the limits over which the 

 theory may appear applicable as the geological survey 

 of the island proceeds. 



Whik we may, in the opinion of the writer, safely 

 accept the theory for the restricted area, it must be 

 borne in mind that changes are continually being 

 effected. The cycle of erosion now operative has cer- 

 tainly modified the former features, but the main scheme 

 of existing topography seems to correspond closely 

 with that which obtained at the close of the Cambrian 

 period. 



Tlie physiography of the central western area has 

 been determined by erosion rather than by structure, by 

 epigene rather than by hypogene agencies. 



This account of the physiographical history of the 

 Pre-Cambrian has been written mainly from the evi- 

 dence afforded by the central western area, since the 

 writer is most familiar with that area. Alodifications 

 may be necessary with an increase of information, but 

 it is contended that this historical outline is substan- 

 tially correct. 



